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Boron: boranes in organic synthesis annual survey covering the year 1980
165
BORON: BORANES IN ORGANIC SYNTHESIS ANNUAL SURVEY COVERING THE YEAR 1980* Cl. S. Matteson Department Pullman,
of Chemistry, Giashington
Washington
99164
State
University
(U-S-A)
CONTENTS INTROOlJCTION
166
B. BORANE REAGENTS
166
A.
2_ Mechanism and Theory
166 168
3.
Trialkylborohydrides
170
4.
Asymnett-ic
1.
Agents
Hydroborating
Hydroborations
170
and Reductions
C. CARBON-CARBONBOND FORMATION
172
1.
Homologation
2.
Alkenylborate
3.
Boron-Substituted
4.
Al lyl boron Compounds
182
5.
Enol- Borinates
186
6.
Boraadamantanes
187 189
via
Borate
172
Complexes
Rearrangements
176
Carbanions
181
D. HYDROBORATION-OXIDATION 1.
Natural
Products
2.
General
Synthetic
3.
Studies
189 190
Applications
of Oxidative
193
Processes
194
E. REFERENCES
-*Previous
survey,
: Relerences p_194
see 3.
Organometal
Chem.,
207 (1981)
13-65,
this
section
40-65.
166
A. INTRODUCTION The leading
contributor
to this
field
has continued
should
still
be fresh
Brown, whose i979 Nobel Prize whose tiork is cited
number and diversity
properties
and synthetic
of organic
utility
of hydroboration
but is rapidly
Herbert C.
memory.
Many of other1
in this survey are former students of Professor Brown.
increasing largely
to be Professor
in everyone’s
of organoboron
chemistry
expanding-to
compounds.
a more broadly
This field
the uniqus
once consisted
of the resulting
based variety
However, an'
to discover
trialkylboranesi
of organoboron
with the most general
in this reviews
survey but are cited
at the end of section
with the top i !
B-1.
8. BORANE REAGENTS
I. Hydroborating
Agents
Hydroboration search for highly
specific
conversion syntheses
is such a useful
new, more selective
Zweifel
compoun$
transformations.
Reviews have not been grouped separately to which they belong,
are beginning
and transformations
include
and wider range of synthetic
chemists
reaction
that considerable
hydroborating
agents.
effort
continues
Some are designed
ji :I .i ii I! on the ;i
to accomplish
$
objectivesand Pearson have reported
the preparation
to mixed thexyldiorganoboranes,
of thexylchloroborane
which are useful
intermediates
and its
;;
in ketone
:.
Cl]-
8Hp + HCl
Et20
)---I-
HH 8 ‘Cl
H$=CHR
R’Li or
1. NaCN
‘CH2CH2R -
B ‘Cl
>
R’MgX
2 . I
3. H202
0 II
RC H2CH2CR ’
An illustrative fir
tussock
application
of this
chemistry
was the synthesis
of the Douglas
moth sex pheromone. 1. CsH17CH=CH2
(CH2)9CH3
8HCl 2. C+-$l\C=C/(CH2)3M9C1
H’
‘H
')-I--
B’ ‘(CH 2 13>=C411 H’
\H
i
167
NaCN, PhCOCl,
H202
! CH3KH2)g-C-(CH2)3,C,C,CSHII
>
H’
Brown and coworkers tion
have prepared
of tetramethylethylene
regioselective
than
also
used
from
Zweifel’s
with
thexylchloroborane
for
in
approach
thexylchloroborane-methyl
H2BCl-SMe2,
thexylborane
‘H
and have found
hydroboration
a synthesis
of
sulfide the
of olefins
ketones
in the use of hydroboration
to
[2].
[3].
by hydrobora-
reagent
to be more
Brown’s
Note
that
introduce
the
this
last
group has differs
alkyl
group.
RCH=CH2 f
F-l-
B
H2BCl-We2
-
BHCl-SMe2
P
K+-HB( O-L-Pr)
‘CH2CH2R
R’CH=CH2
W,CO),O
H202,
-NaCN
3
FHZCHZR >
1,4-Oxathiane-borane
II ! I
than
is
dimethyl
B\
F-l-
OH-
CH$H2R
! RCH2CH2CCH2CH2R’
---
odoriferous
A
a new convenient
hydroborating
agent
[4].
It
is
less
sulfide-borane.
owS-BH3
‘The 1,4-oxathiane selectively
I$rialkylborane “xidizing
remaining
oxidized the
product sulfide
after
hydroborations
by hypochlorite
Conversely,
[S]. if
to water the
with soluble
its
borane
sulfoxide
trialkylborane
the medium is made sufficiently
complex without
can be oxidized
1
within
an hour.
In contrast,
HBBr2-SMe2 and HB12-We2
apidly and hydroborate olefins such as l-octene or cis-3-octene % The reagents are easily kefluxing CH2C12 without any catalyst. ciX3 to BH3-SW2. ith [
X3
dimethyl
The hydroboration
sulfide,
from which
products, the
free
the
without
basic.
! Brown and coworkers have reported that HBCl2-SMe3 hydroborates I _iively slowly, and requires an acid catalys t such as BC13 in order leaction
can be affecting
react
relathe
much more
within
a few hours
prepared
by adding
RBX2, form distillable
RBX2 may be obtained
olefins
to complete
in
complexes
by treatment
with
C61. Reaction hydrolyzed
of HBBr2-SMe2 with to boronic
acids
alkynes
or coupled
yields by the
alkenylboron
dibromides,
use of methylcopper
which may
to form symmetri-
168
-i-Pr
i-Pr-CXCH3
The useful yield
>
+ HBBr2-SMe2
hydroborating
by refluxing
agent
BH3-SMe2 with
Dicyclopentadienyltitanium lithium
alkylborohydrides
mixture
of
agents
is
g-alkyl-
Brown’s
The chemistry
c121.
reacts
with
of
>
'BBr2
produced
amount of
catalyzes
hydroboration
of
has been carried
Pmong the more exotic alkenes
quantitative
CC14 [8]-
the
Hydroboration
in nearly
or acetylenes
alkenes
out with
to a
hydroborating
at 80°C to form
[ll]_ has been republished
“Hydroboration,”
book,
c=c
an equimolar
by LiBH4 [9]_
which
3 CH3Cu
,CH3
BH2Cl-SMe2 is
dichloride
or 9-alkenyl-6-SB9H11
chemistry
H’
NaBH4 and SnCl4 in THF [lo]. 6-SB9Hll,
\
9-BBN has been reviewed
with
his
Nobel
Odom has reviewed
[13].
lecture
added
organoboron
[14].
2. Mechanism and Theory Significant both
additions
experimental
Structural
to our
and theoretical
characteristics
of
Wang and Brown have used boration
with
rate-limiting
knowledge
hydroborating infrared
is
the
the mechanism
agents
dissociation
are
spectroscopy
With reactive
9-BBN in CC14 [15]. step
of
of
hydroboration
from
of view have been made during the past year.
points
of
also
to follow olefins
(9-BBN)2
to
included the
in this
kinetics
section. of_ hydro-
such as cyclopentene,
the
2 9-BBN, and subsequent hydro-
boration of the olefin is rapid, resulting in kinetics first-order in (9-BBNJ2 and zero-order tion
in olef i n-
becomes
reversible,
order in olefin.
The kinetics l-butene.
With less resulting
reactive
olefins,
such
as cyclohexene.
the dissbcia-
in kinetics half-order in (9-BBN)* and first-
Olefins giving intermediate kinetics were also found.
of reaction
and cyclopentene
of 9-BBN with
1-hexene,
have been measured [16].
P-methyl-petitene,
3,3aimethyl-
169 Relative measured 4.49,
which
styrene,
rates
of hydroboration
by Vishwakarma corresponds
in accord with
more than
of substituted
to a slight. buildup the
idea
97% R-phenyiethanols
styrenes
A Hammett plot
and Fry [17]. that
the
of positive addition
by 9-BBN in THF have been
using
D* gave a value
charge
on the
is electrophilic-
of
p=
s-carbon
of the
The products are
cases.
in all
Calculations on the reaction of BH3 with C2H4 have been carried out at the 4-316 level, which represents substantial improvement in accuracy calculations of the
The mechanism involves
[18].
subsequent
rearrangement
n-complex,
rearrangement
which
of this
slightly
will
good agreement
Fehlner’s
sition
state
with
geometry
bring
the
experimental
is calculated
activation estimate
that
further
for refinement
energy down to 4 kcal/mol, in
(JOM 41 (1972)
to be a slightly
and its
energy for formation
of a few kcal/mol
It is expected
estimated
previous
of a n-complex
is no activation
and a barrier
exothermic,
complex to ethylborane-
of the calculations
formation
two steps, There
to ethylborane.
over
distorted
65-66).
The tran-
parallelogram.
transition state
a-complex
A semiempirical MO study of the mechanism of hydroboration has been published
c191.
Molecular orbital calculations on B2H6 have indicated
lation
is a major
contributing
factor
Brown and Wang have studied differing
steric
requirements
the
to the dissociation
that
energy
electron
corre-
[20].
association
of 9-BBN with a series of amines of 13C NMR [Ei]. The symmetry of the 9-BBN by the use of
system is diminished by complexing, and systems were found in which the amine complexes
either
did
at equilibrium,
dissociated
not dissociate,
or were not formed
detectably,
rapidly
and reversibly,
depending
on the
steric
amine.
+ NR3
knonequivalent
7
.?
equivalent
P
were not favored bulk
of the
170 derivatives typically show l3 C NMRspectra
9-Substituted-9-BBN
the 9-BBN group has the full stituent
9-BBN ring carbons, the
symmetry expected
on the boron introduces
two sides
[ZZ].
corresponding
and pyridine
complexes
indicating
The presence
diastereotopic
that
of a chiral
nonequivalence
subin the
of 9-R-9-BBN show nonequivalence between
of the 9-BBN unit.
3_ Trialkylborohydrides
Lithium triethylborohydride ing even lithium have reported chlorides, reagent
aluminum hydride
the
lactones,
groups [23-J,
for
reducing
quantitatively
powerful
in some respects.
epoxides,
tertiary
halides
to alkanes
agent,
surpass-
compounds, acid anhydrides
amides-to
Lithium triethylborohydride
alkyl
reducing
Brown, Kim, and Krishnamurthy
LiHBEt3 to reduce carbonyl
use-of
esters,
functional
is an exceptionally
[24].
alcohols,
and
and various
other
is a particularly
effective
Primary iodides
are reduced
in minutes at 25OC, bromides in a few hours.
Cyclohexyl
iodide
is 63%
reduced in 24 hr. Lithium trialkylborohydrides are readily formed by reaction with t_butyllithium as the hydride source [25]. R3B f (CH3j3CLi
The reaction
R3BH- Lit
+
proved successful
but also with hindered
+
of trialkylboranes
(CH3)2C=CH2
not only with the usual alkyl
and cycloalkyl
boranes such as P&Me-9-BBN, B-isopinocampheyl-9-BBN,
groups, and
thexyllimonylborane. The crystal
structure
sodium and hydride each hydride
of
(NaHBEt3)4-Et20 has been determined
hydrogen atoms occupy alternate
coordinated
to one boron and three
4_ Asymmetric Hydroborations
enantiomeric
excess
hydroborates
specificity, (e-e.)
The
of a distorted
cube.
with
sodium atoms.
and Reductions
Monoisopinocampheylborane high degree of chiral
corners
[26].
yielding
phenyl-substituted alcohols
after
tertiary
oxidation
olefins
[27]_
Ph 100% e.e
.H
Ph.,,, H--$ CH3.
-C+H
8l% e-e tH3
with a
having 81-100%
l-71
Ph\
AH3 c=c
CH3/
‘H
omeric
and
coworkers
=,t+acetylenic excesses
smaller
were
successful
have
ketones in
substituent
proved
82% e-e,
H +-C&H,
I+
+.__ H
cl-i;
Midland reduces
*OH
Ph-e,+
in
the
the
to
that
alcohols
range
l3-3-pinanyl-9-borabicyclo[3.3.l]nonane
with The
73-100%.
high
ketone
group
of
stereoselectivity
acetylenic
series of reactions.
this
with
reported
This
group asymmetric
RCOCZC02R’
Enanti-
[28]is
the
sterically
reduction
has
also
1291.
R ._ R --0
--*“*W R’csc-
i-D
6
ex
•t
v
Midland readily
and
available
diethylborane base and
and the
Preston by
or
oxidized
of
the
the
borane
to
mode of
alkyl
then the
z-3-hydroxy-l-octynyl
corresponding
allylic
migration
acetate,
ketone
rearranged
the
alcohol
[3O].
was &,
with product The
yielding
which
is
dipinanylborane, by treatment product
was
material
with with
all
having
excess.
yH R
OAc $ HCD-S-
hydroborated
dicyclohexylborane,
predominant
enantiomeric
have
reduction
R2BH >
C5Hll i
OH-
R2B\ /H H,C=C\CdOA~ H’+.C
H 5 11
R-B $’ H4
lCHH II H/CN C5Hll
Ho,;
“2O2
>
H&-.C/H II . H&
References p_ 194
H 5 11
trans., 50-74%
172 Factors
involved
been discussed
in chiral
from sodium borohydride, Stereoselectivities Directions
for
ketal
types
C-5, hydroboration
of a-pinene
synthesis
of asymmetric natural are covered
includes
alkyl(a-haloalkyl)borate
formation complexes,
and cyanidation Oxidative
acids
[32,33-J.
of the resulting
acid to form 3-pinamine
are
has been cited in sections
included
products
and control
carbonylations,
in ketone syntheses
rearrangements
promise of synthetic
condensations
have been
in section
B-3
C-l,
C-4, and
of relative
chirality
utility,
(sections
of organoborane boronic
esters
bonds by rearrangement and cyanidations.
have already
of alkyl(alkenyl)borate
of
Examples of
been cited
complexes,
in section covered
in
somewhat related. and together
These types of reactions with allylboron and enol
C-4 and C-5) constitute
chemistry
Matteson and Majumdar have reported to a-chloro
and cleavage
of carbon-carbon
C-2 and C-3, are mechanistically
borinate
prepared
via Borate Complexes
This section
applications
have
in part D-l.
Homologation
show great
with reagents
and carboxylic
of asymmetric trialkylborohydrides of asymmetric
CARBON-CARBON BONDFORMATION
sections
reactions
[34].
1.
B-l [1,3-j_
of glucose,
with hydroxylaminesulfonic
C.
carbonylation
have been accomplished
derivatives
Syntheses
The preparation
by hydroboration
of ketones
the hydroboration
in Organic
Other
and other
were in the range 12-64% e-e.
diisopinocampheylborane
[25].
in hydroboration
[31].
Asymmetric reductions
published
selectivity
to organic
the fastest-growing
field
of
synthesis.
the efficient
with dichloromethyllithium
homologation
of boronic
The process
[35].
esters
involves
the
same type of borate intrmediate as the reaction of RLi with C12CHB(OR*)2 to form R-CHCl-B(OR’)2, first reported by Rathke, Chao, and Wu [JOM 122 (1976) 145]_ However, starting
from RB(OR’)2 and C12CHLi opens up a variety
of new synthetic
possibilities. ,O-CR;
R-B i ‘O-CR’2
+
R = primary,
secondary,
/o
t-BuCH-B Cl ‘0
LiCHCl2 B
-I-
R
-100 “c
tertiary
PhS
25 Oc >
C12HC alkyl.
R-CH-B
I Cl
cycloalkyl,
/O
> t-Bu-CH-El, I 0 SPh
vinyl.
allyl,
benzyl;
and similar
R’ = H, CH3
displacements
R = Ph, Bu, cyclohej 3 Cl
173
H2C=CH-CH-6,
10
I
H2C=CH\ ,CH-B &-Bu02CCH2
LiCH2CO2-t=Bu
0
>
Cl H2C=CH\ ,CH-CH-B t-Bu02CCH2 I Ci
Bu-$H-6. PhCH20
LiCHC12
/O
Extension promising esters
of this
new type
was found
isomeric
purity,
utility
of this
isomers
of
thoroughly
,O
PhCH20
“
chemistry
of directed
except
where
characterized
=
Ph-B
Cl
chiral
>
by Cram for
esters
by Matteson Homologation
having
high
group was methyl by the
purity, his
[36].
esters
the migrating
Bu-:H-C,H-CHB PhCH20
synthesis boronic
in high
NaB03
’
was demonstrated
3--phenyl-2-butanol
CH3MgBr
to pinanediol
to give I-a-chloro
approach
3 ‘0
‘0
/O Bu-$H-C\H-B,
>
LiCHCl2
,O
synthesis studies
of
they
to a
(+)-pinanediol diastereo-
The potential
of both separate
chosen because
classical
and Ray has led
(83-97%)
(74%).
OH
diastereo-
had already
of nonclassical
been
ions.
Ph-B
CH3
CH3
CH3
CH3
1. BClB 2.
H20
, H 1
H (-)-pinanediol Ph +?(OHJ2 F CH3
Boronic esters
H f = -
-
ZH,
esters
in high yiel,ds
Referencesp.194
Ph+-B
M
IO> YoJ.-)
are
homologated
[37].
by Me3SiCHC1Li
to a-trimethylsilyl
Ph-g
tH3
-@OH T iH, H
boronic
174
Me3SiCHCl
+
/O R-CH-B &. ‘0 Me3 I
+Cl
R = c-Bu,
/O R-B ‘0
set-Bu, -
cyclopentyl,
* Me3SiCHCl
cyclohexyl,
P R-CH-B ‘0 I #Me3Si
->
R = CH3CH=CH-, CH2=CH-CH2-
Larson
and coworkers
borane
with
Me3SiCHBr + R3B
75-78 %
have found
homologation
intermediate,
that
trialkylboranes
of one of the &-alkyl
which may be oxidized
->
H202 NaOH
R-lH-8R2
+- R38
with
Me3SiCHBrLi
or
to form an a-silyl a-silyl
alcohol
[38].
R-$H-SiMe3 OH
H2°2 NaOH >
R-fH-BR2
+
react groups
to the corresponding
Me3Si
PhMe SiCHCl 2
x
PhCH2, PhSCH2
+
PhMe2SiCHClLi
77-87
R-FH-SiMe2Ph
PhMe2Si R = primary,
Two alkyl leading
secondary,
groups
or cycioalkyl
are transferred
to a synthesis
from R3B in the
of symmetrical
reaction
with
silyldialkylcarbinols
PhMe2SiCC12Li,
or ketones
[39].
2H202 PhMe2SiCC12 + R3B
,->
PhMe2Si-CR
cr207 PhMe2Si-CR , 2 -
NaOH ’
R-SC:
A simple reduction
homologation
has been reported CO, LiHAl(OMe)3
of 9-R-9-$BN by Brown,
to 9-RCH2-9-BBN Ford,
by way of carbonylation
and Hubbard [40].
Li Al H4
CH3S03H
R-B 3
R2C=0
OH
_20--
>
-
R-CH2-B =c):. _’
R = c-octyl. cyclopentyl.
cyclopentyl.
cyclohexy‘i.
cyclooctyl.
exo-2-norbornyi:trans-2methyl.._
.-..
and
175 KHB(O-i-Pr)3 ylation
has been found
of trialkylboranes
to be a superior
for
reductive
carbon-
c411.
+ CO + K+ -HB (O-i_+?-)
c.B<
reagent
3
->
H2o2 CHO
CH20H o-
has used the reaction of cyclic
Kabalka
to introduce
13C and l4 C labels
0-f
trialkylboranes ketone carbonyl
with KCN/(CF3CO)20 groups [42].
RBH2 >
II
I
into cyclic
R = thexyl
1.
K*CN
2.
( CF3CO)20,
3.
H202lNaOH
.
Hydroboration-cyanidation (*)-estrone
methyl
ether
has been used as a key step
in a total
synthesis
[43].
BH2 A
KCN -.(CF,W,O
H2°2
of
CH30
The conversion
of 9-BBN to bicyclo[3
CH30CHC12and Et3COLi followed Organic Syntheses 2. Al kenylborate the alkyl
control _ other
by oxidation
has been described
with in
in detail
Rearrangements react
electrophiles,
first followed
Examples have already
with various
groups,
and alkenyl
This section
generally
covers
electrophiles
by rearrangements
been cited
in sections
followed
_cyclopropanes
[45].
PMe CH2=C=C ‘Li
+
by rearrangement
or oxidizing
agents to
with a high degree of stereochemical
rearrangements
initiated
catalyzed
by protons,
iodine,
by transition
or
metals.
B-l [7] and B-4 [30].
A group led by Suzuki has found that reaction l-methoxyallene
by treatment
[44].
Alkyl(alkenyl)borates join
_3_l]nonan-g-one
of g-alkyl-9-BBN’s
with acetic
acid yields
with l-lithio-
l-alkyl-l-methoxy-
HOAc
R-B
>
>
,OMe HOAc B-CH2-CH=C, -> R
@-OAc
+ BT 63-7s
R = l-alkyl.
cycloalkyl,
Reactions has yielded
exo-norbornyl,
trans-2-trimethylsilyloxycyclohexyl
of anions from trisylhydrazones
vinyltrialkylborates,
l,l-dialkylethenes
of methyl ketones with trialkylboranes
which rearrange
on treatment
with iodine
to form
[46].
\ R;B CH2=C-R
>
R’3B-i=CH2
-.
177 7 ‘2
R;
>
R/C=CH2
l,l-Dialkylethenes organoboranes TiCl4/Ti
have been prepared
by treatment
(0-i-Pr)4
with
from 1,2-dimethoxyethenyllithium
C13CC02H followed
[47].
R3B
6uLi MeOC=CHOMe I Br
MeOC=CHOMe
5
Cl 3CC02H R3D--
I
R-F
MeOC=CHOMe
- CH20Me
NaOAc Ac20
R2C-CH20Me
TiC14
->
OHR2C=CH2
ri-
(can be oxidized
Yields
to
Isomeric
R2CHOHCH20Me) 2-Bu,
_1_pentyl.
Levy and coworkers olefins
.->
OMe
R-;-OMe
followed
>
R27
>
R =i-Bu,
and
by NaOAclAc20 and
cyclopentyl,
have found
by iodination
to provide
IL-hexyl,
that
45-78 x purity
89-100
%
cyclohexyl
9-alkyl-9-BBN
a stereocontrolled
reacts
with
synthesis
alkenyllithiums
of trisubstituted
[48].
/ C6H131C=C /”
f
R-B
>
3
‘Li
Et’
f ; ! 1
1
2
This
c=c’ ‘R
Et/
stereochemical
behavior during
H
‘6”131
;---+
outcome is
of trans-alkenylboranes the
12.and
NaOH, but hydroxide
-.
:.
on the
basis
by Suzoki’s
group [49].
with lead(IV)
of the
is not present
case.
of (1-halo-l-alkenyl)dialkylboranes
(AcOj21Ph h&e been studied Refe&ncesp.194
toward
in the present
iodination
Reactions
not what would have been expected
acetate
or
178 R2BH ->
BuCXBr
B”\
c=c
H’
Pb(OAc)4
,Br
8”, >
'BR2
H'
PhI(OAc)2
or
R = cyclohexyl,l,Z-dimethylpropyl
R’
B",
->
= primary
-n-hexyl,
alkyl
CH2Cl2
,Br
95-98
Yield
40-58%
B",
>
c=c
H'
,Br 'RI
%I
H’c=c’BR’;g;
96-97
Yield 0 Oc
Bu,
P-methylpentyl
54-65%
,R’ c=c
H’
%L
‘Br
90-96
Yield
R12BH ->
B”\
->
c=c
H’
R ‘+I-hexyl
Lithium methyl
'R
%Z -
n_octyl
BuECCl
,Br
Pb(OAc),
R'2BH BuEC-Br
c=c
/C ’
ketone
R3B-EC-Ph
the
B
CH2=CH-CCH3
+
0
in
presence
rearrangement of
titanium
TiC14
%
independent -Z isomer, of conditions
‘R’
l-alkynyltrialkylborates‘undergo
vinyl
35-55
tetrach?oride
and
Michael
addition
to
[50].
co1
-+
E
II R-C-fH-CH2CH2CCH3 Ph
R = alkyl;
similar
results
Alkenyldisiamylboranes Pd(PPh8)4
R-ECH
to
+
form
HB(Sia
and
alkenes
)2
with
B
ally1 or benzyl halides have been coupled with
[51].
R, H'
C/ 'B(Sia)2
-. :
..
179 CH2=CHCH2Br
R\
A
,H
HHC=C’CH2CH=CH
2
PdW’h,),
NaOH filkenyldialkylboranes molar
derived
amount of palladium
dialkylboranes
derived
of palladium
acetate
from terminal
acetate
from
acetylenes
and triethylamine
internal
acetylenes
are
rearranged
to form E-olefins are
cleaved
by an equi-
[52].
Alkenyl-
by even a catalytic
amount
to form -Z-olefins.
PhCXH + HB(Sia)2
Ph,
.->
Pd(OAc)2
/”
c=c
H/
Ph\
‘B(
Et3N
Sia),
’
c=c
H’
/” ‘Si
a
Pd(OAc)2 BuCZCBu
If
+
HBU
(cat.)
H’
‘B(Sia)2
THF
c=c
9-BBN is
coupled
Bu,
used
with
as
ally1
the
agent,
hydroborating
Bu,
c=c
H’ (solvent
the
internal
,Bu ‘H is proton
alkenylborane
source)
can
be
cross
and
cross
chloride.
Pd(OAc)2 (cat.) ““,r=c<,“”
+ CH2=CHCH2Cl
Bu ‘C& H/
p>
Bu ’ ‘CH2CH=CH2
3
Catechol coupled
with
alkeneboronic allylic
esters
bromides
have
in the
been
presence
treated
3CH3Li
R, ,H c=c ,o H’ ‘B
with
methyllithium
of CuI (533.
CH2=CHCH2Br
R
/H
‘CCC’ H’
‘CH2CH=CH2
‘0
R = alkyl,
Crotyl
Ph
bromide
89-97%
gave
complex condensation
R\ -H’
c=c
/H
a mixture
isomers
(46:52).
Propargyl
bromide
gave
more
HCXCH2Br
GUI
+4 -30
‘B
‘0 a
“c
’
:2=cc:,
--
40-55%
-. Referencesp.19k : .:
allylic
products. 3CH3Li
p
of
CH CHiC=CH 2
2
180 Yatagai copper
at
has found
-40
predominant reacted
to
similarly
to couple philic
-30
product
that
treatment
‘C followed (73-86%)
butyl
iodide
with
by allylic
is that
at 0 OC, with
cocatalyst
of dialkenylchloroboranes
the
halides
formed with
87-92%
allylic
yields
allylic
It
inversion.
or PhSLi.
Yields
3 mols of methyl-
1,4-dienes
[54]-
inversion.
organocopper.intetmediate
such as P(OEtJ3
with
was also
in the
found
possible
of a nucleo-
presence
were generally
The
Alkenyl-9-BBN
50-60%.
R R = H, Ph, CH3; X = Cl,
Hydroboration alkenylboranes
of acetylenes
with
and Brown to yield
obtained
by hydroborating
t-butyllithium,
the temperature tured
with
ally1
with
NaOCH3 followed
Campbell with
(major
Br
with
NaOCH3 followed
OC, the organocopper to form 1,4-dienes
intermediate
+ HB
VB
Bu “=‘<,.,
,H ‘BU
H’
BUEI
NaOCH3
+
r
La
BH 2
CuBr-SMe2
NaOCH3
CuBrSMe2 >
> ,-15
Oc
by CuBr-SMe2.
resulting by
By lowering
can be stabilized
in a stereospecific NaOCH3
Bu-CXH
of the
[55]. A -Z,Z-diene has been --E,E-dienes with dicyclohexylborane, reducing the iodide
I-iodohexyne
bromide
by reaction
by CuBr-SMe2 at 0 ‘C has been found
symmetrical
and treating to -15
9-BBN followed
isomer)
manner [56].
CuBr-SMe2
and cap-
Yamamoto and coworkers RCu-BF3 reagents high
ratios
pattern
(see
have published
allylic
of &attack
[57]
RCH=CH6R’$uf RBF$u+
with
halides,
a full
of R on the allylic
JOM, 180 (1979)
was noted,
and it
account
acetates, group,
regardless
Similarity
48).
was suggested
of the
and alcohols,
to the
that
the
of the
behavior
reaction
of
generally
give
substituent
of
may involve
as an intermediate. THF *b
IL-BuCu-BF3 + CH3CHAHCH2Cl
n-Bu, CH/CH-CH=CH2 3
Et20 &BuCu-BF3
(excess)
+ (CH3)+CHCH20H
(98% of product)
S”3 fi-Bu-C-CH=CH2
e-3
I
Dimesitylalkylboranes resulting
anions
are
deprotonated
have been methylated
by lithium with
dimethyl
MespBCH2-
_____)
(100% of product, 70% yield)
CH3
the
reactions
which
in THF and
dicyclohexylamide sulfate
[58].
(CH312S04 NLi 2
Mes2BCHg f
-3
CH
Mes2BCH2Ph
->
Mes2BCHPh
&
->
W
Mes,BL-ih ZH3
EH3 Mes = 2,4,6_trimethylphenyl
Pn efficient aldehydes,
homologation
of aldehydes.
R2CO to R2CHCH0, utilizes
RCHO to RCH2CH0, or of ketones
LiCH(i302C2H4)2
159-j.
R,
/H C=c, P B. 0 (not isolated) H’
NaB03
pHic i Referw+194. :
RCH;ICHO
.- :
,
to
182 Deprotonation lithium alkyl
halides
esters
of pinacol
trimethylsilylmethaneboronate
2,2,6,6_tetramethylpiperidide or condensed with
and.the aldehydes
has been accomplished
resulting
to yield
anion
has been alkylated
predominantly
with with
Z-alkeneboronic
[60]. LiTMP
p-
MeSi CH2B,
/o Me$iCHS,
>
0
O-i-
RCHO
R\ H’
SiMe Allylic
Bu3SnCl at the
,
‘H
70% cis
3
anions
are useful
S/O ‘0
GC’
+-
derived
l-position
from l-
or 2-alkenyl-9-SSN
to form almost
in erythro-selective
coupling
exclusively with
‘C&’ H’
or
derivatives,
which
Bu3Sn >
r\
H20
\SnSuS
p
>
‘H
Me3SiCl
[61].
)
cc
Pr
with
Z-allylmetal
aldehydes
-____-PrCH2CH=CHB
react
H2NCH2CH20H
C=C’ H’ ‘H
CH SnSu3 2
PhCHO
R Ph
‘r-J” OH
4.
Allylboron
compounds
The use of allylboronic
esters
by R. W. Hoffmann and coworkers. ceding
section
in stereocontrolled Related
chemistry
synthesis has just
has been developed
been cited
in the
pre;-
_ :
[61].
.-
:
_
,,
:
.’
.:
..
183
‘Hoffmann and Zeiss to achieve
chiral
have been used the
synthesis
of alcohols
allylboronic
useful
ester
in natural
reaction
products
with
synthesis
aldehydes [627.
Y cH31C=CA ” 0 H’ \8’ ‘0
=
C”3lC=C
Et+CHO <
1” N/I
H’
‘01
*
92% of product
8% of product
56% of product
44% of product
CH
I 3 ” - C,;++$C~ Transi.tion
state:
H I,,” _ __B,O 7*
R‘..^_+=o---A (derived
I and E_r-a’IkylthioalJylboronic
\O/
from cis
esters
boronic
react
ester)
highly
diastereoselectively
HO
-J+ I
R
SEt
with
184
RCHO EtS w
= z
Reaction
esters with aldehydes yields
of 1-butene-3-boronic
The -isomer L-homoallylic alcohols [64]. esters such as the pinacol ester are used. the a-methyl
substituent
into
BP ‘0
+
an axial
predominates Interference
conformation
if
mixtures
sterically
by the.pinacol
in the transition
Allyltrialkyltin esters
group forces state.
compounds react
-i-Bu,
with 2-chloro-1,3,2_dioxaborolane
Ph
to form allyl-
[65].
yQnBu3 + $1
SnBu3 + CIB,
-
y4y)‘,73x)
CH2Cl2
/O
W
boronic
RCHO p>
R = Me, i-Pr,
boronic
of g-and
hindered
>
0
P
WB\
0 (Slta)
+
/-7-8;;1
+ “0“) (10%)
(17%)
_.
:
-- -.
185
Reaction the borate threo-
of crotyllithium
complex
selective
with
followed
triethylborane
by reaction
condensation
with
or tributylborane
an aldehyde
results
to form in a highly
1663. PhCHO
+
BEt3
H 7
Carbon-13 allylic
NMR spectra
y-carbons
hyperconjugation
of allyltrialkylborate
and deshielding with
the
allylic
complexes
of the
a-carbons,
system
[67].
BR;
show shielding
an effect
consistent
of the with
C-B bond
BR3
Allyldialkylboranes
+H=CH-CH2BR2
-
BEt3-
Li+
l
EtO,
Fl C H’ ‘BR2
add to ethoxyacetylene
HCZC-OEt
+
fH3
$“3 CH,
3 trialkylborane-ethoxyacetylene
CH3
[68].
Bto\
C9H190H
C/CH\cH
H
2
adducts
can be converted
2
H
to allylacetylenes
[69].
Et3A1
I
HCZC-CH-CH=CH2
I
1
80-110.
tH3
ti BR2
‘ther ,examples loraadamantane .References p. 194
of related
chemistry: ---
: :.
..
allylborane
chemistry
are
included.in
section
C-6
on
186 5,
En01 Bori nates Boronic
esters
of enols
or dialkyl(alkenoxy)boranes
nized as being among the most useful sations,
which are useful
Evans and Taber synthesis 45-83%
in syntheses
have reported
of
the
isomer
are
intermediates of macrolide
the
The most favorable
[70].
content
of
for
becoming recogaldol
conden-
antibiotics.
use of chiral
boron enolates
case is illustrated.
corresponding
rapidly
stereodirected
Other
in directed
examples
to the one illustrated
chiral
ranged
as the major
from isomer-
(CH3)zCHCHO
--p-f-
\\ 0
-
?--
Ts
OBBu2
?+A
* Major
isomer Hirama
aldehydes
Minor
(> 97%) and Masamune have described
with
the
the &-and L-dialkylboron
0
(&SHg)$JOTf
II
CH3CH2C-S-t-Bu
0
OH
isomer
(< 3%)
Ts
stereoselective
enolates
enolate
of CH3CH2COS+3u
,OR(CgHg)2 C=C CH3’ ‘s-L-6u
of
[71].
RC”0 >
“1
______3 i-PrzNEt
condensation
R cos-t-Bu
s Hi
RCHO CH$H=C=O
+
j
Bu26S-t-Bu
-
COS-t-Bu
-
The preparation
of dibutylboron
These reagents react c721. to generate one regioisomer aldehydes
with
high
regio
with
and the
permits alkylation
alkylation are
and 9-BBN triflate
enolizable
of the enolate
ketones
in the
selectively,
has been described
presence
of tertiary
and the enolates
amines
condense with
and stereoselectivity.
Ho02 and Oudenes have found borinates
triflate
that
C73-J.
regiospecific.
addition Both the
of
LiOCH2CH2NMe2 to enol
reaction
used to form the enol
borinate
187
BBu2
9
0
RX
BuCH=C-CH3
BuCH-:-CHS
LiOCH2CH2NMe2
(from
N&HCOCH3
R = CH3,
d
and BBuS)
PhCH8, CH@HCH2,C2HS
Enol borinates readily
react
converted
regiospecif
with
PhSeCl at
-78
to a,s-unsaturated
‘C to form a-phenylselenyl
ketones
ketones,
The over-all
synthesis
which
are
is
ic.
‘jB(CH2R’ )2 R-C=CH-CH2R’ (from
[74].
+
PhSeCl
I:
p>
RCOCH=N2 + B(CH2R’ ),) 0
->
R-:-CH=CHR ’
Lithium potassium
enolates
enolates
from ketones
readily
fail
to react
with
form borate
complexes
[753.
6,
l
(CH&C-t=CH2
.-
Boraadamantanes This
field
has been created
trialkylboranes tane-like this
can be elaborated
structures
organoborane
having chemistry
discussed
in
by borane
carbonylation,
this
his work in this
review, field
A boraadamantane [77],
but the
-BR~K+ P (CH3)3C-C=CH2
O-K* R3B
trialkylboranes,
Carbonylation
by Mikhailov with
a tetracoordinate to synthesis
but
it
as well recently
does
in English
or acety’lenic boron at
a novel
cyclic
who discovered reagents
one apex.
is not as general
provide
as other
has been synthesized and oxidation
and coworkers,
allenic
route
compounds.
The applicability
as most of the other to adamantane Mikhailov
+
(CH3)2C=C=CH2
of topics
derivatives
has reviewed
[76]. from triallylborane
has yielded
the
and l,l-dimethylallene
corresponding
1-hydroxyadamantane. t
B(CH2CH=CH2)3
that
to form adaman-
s
w
.-. @
Triallylborane condenses with propargyl ethers [7&
2.5'C, RO-CH2CECH
i-
791.
ROCH2m,
130 'C_>
B(CH2CH=CH2)3 CH2C"=CH*
Triallylborane undergoes cyclization with l-methoxypropyne Cf301-
+
CH30C=CCH3
100
B(CH2CH=CH2)3
0;
140
crk$-Jq 3
Oc >
~H~CH=CH~
CH30H +
%
,,,g
&8(OCH3J2 3
Tris(2methylallyl)borane propargyl
HECCH20CH
ether
shows
140 3
+
similar
behavior
to
triallylborane
toward
methyl
[Sl].
WI2
-CH213 F
CH30H
Oc
-
CH20CH;
d
H3 I
THF BH3 THF
More details of boraadamantane synthesis have appeared [82]- The dimethylated boraadamantane derived irom the
THF and
pyridine
complexes
tricrotylborane [83].
and
MkOCH$XCH
has
been
synthesized
as
189 I_
L = THF or pyridine
I
Treatment of ination
lithium
I-alkyl-1-boraadamantanates
with cage opening
[84].
Bromination
with acetyl
[SS].
ing carbonylation
Several
reactions
and oxidation
results
in elim-
of 1-boraadamantane opens the ring to
form a bromomethyl compound, which can be hydrolyzed B-O derivative
chloride
with base to form a ring-expanded
of boraadamantane have been reported,
to form 1-adamantanol
includ-
[863.
D. HYDROBORATION-OXIDATION 1. Natural Products Hydroboration-oxidation alcohols. tions
This section
of natural
has been cited
covers
products. in previous
sponding amine in section pheromone in B-l [l]
has become a standard the use of this
process
for
synthesizing
in syntheses
and transforma-
Other hydroboration chemistry related to natural products sections, such as the conversion of a-pinene to the correB-4 [34]
or a steroid
and carbonylation in C-l
occuring
plant
of boranes
to make an insect
[43].
has been used in a synthesis
Rearrangement of a trialkylborane which is a naturally
procedure
growth regulator
of triacontanol,
[87-J.
WCl6, Cl 2C=CHCl CH3(CH2)13CH=CH2 F
BH3-THF CH3(CH2)13CH=CH(CH2)13CH3 B
CH3CN, Bu4Sn
Hz02
heat >
diglyme
CH3(CH2)28CH20H
OH-
Hydroboration-oxidation dien-3e-ol oxidation indole
of various
has been used in a steroid
alkaloid
tabersonine
borane as a means of controlling [92].
reactions
synthesis
states
[go].
stereochemical
leading
/ Refere-p-194 :
5a-cholesta-8,14[88]_
Hydroboration-
Hydroboration-oxidation Further
result
dienes
organoboranes.
between separated The utility
of
with thexyl-
from the geometric
of dihydromyoporone
of the
study of hydroboration
of nonconjugate relationships
(80-95~
to cyclic
was demonstrated in syntheses
chain.
example,
[89].
hydroboration
High stereoselectivities
ments of transition
for
has been reported
has been reported
coumarins has been reported [91]. Still and Darst have studied centers
steroids,
to 5&cholest-8-ene-3s.15a-diol.
chiral
requireof these
and the vitamin
E side
190 -- BH2
1.
&-J”
tt+
M 2.
+
H202, OH
OH
=
OH
\ Y,
OH
OH
2,
General
Synthetic
A variety process
are
Applications
of synthetic
sununarized
in this
Hydroboration-oxibation 1,4-diol.s
applications
and general
studies
of the
-
section. of bicyclohexenyls
hydrobor+tion-
ha& been’studies
as a’route
. to ch.iral’
[93]. ,_
(,
..
191
meso only Soderquist vinyl-,
and Brown have reported
propenyl-,
allyl-,
E941- Vinyltrimethylsilane BH3-THF, but 9-BBN yields 91% e-boryl
derivative
95% a-boryl
derivative
usual stereochemical
yields
mixtures
mainly s-boryl
rules
for
H'
isomer.
->
BH3-THF
yields the
CH3CH2$H-SiMe3 OH
of interest
has .been used in the synthesis
as a possible H202
.A_
cytidine
-. ..
of a 1,3_diaiepinone
deaminase inhibitor
H/N o=c B
Ft+ere-pi194
yields
HOCH2(iH-SiMe3
CO1
--
Hydroboration-oxidation
i
2-Propenyltrimethylsilane
C”3
/iMe =iH
derivative
with BH3-THFand 9-BBN
hydroboration.
co1
____3
of
of (L and e-boryl derivatives with
even with BH3-THF, and e-l-propenyltrimethylsilane functions follow with BH3-THF. More remote olefinic
CH3 CH3Lc
study of the hydroboration
and 3-buten-1-yltrimethylsilane
BH3-THF
H2C=Ij-SiMe3
a detailed
~.
[95].
192 Hydroboration-oxidation been
studied
reported
of
benzocycloalkenes
Hydroboration-oxidation
[96].
with
of
diborane
and
thexylborane
a bicyclo[4.l.O]heptene
has
has
been
[97].
d
B2H6
2.
H202
h
Hydroboration synthetic
1.
of
study
allylaziridines
and
vinylaziridines
has
been
reported
in
a
[98].
Ph
1-e B2H6
HOCH2CH2CH2 2.
‘T\j‘
N H
Ph PPh3 3 Br2
1_ 9-BBN
Ph CH2=CH
2. “\j-
N H
H 34 %
Hydroboration been
studied
pentadiene hexadiene of
of
L-991. to to
tion
of
does
and with
3_cyclopenten-l-al. 3-cyclohexen-l-al.
CH3CEC-CH2CH(CH3)2
than
cyclopentene
Hydroboration
attack
of
similar
with
boron
at
and
the
BH2Cl
limonene R2BH gives
3-position of
the
(to
to
followed
norbornadiene
various
hydroboration
norbornene
the
RBH2 and
R2BH stages
by oxidation
converts
to exo-dehydronorborneol, to
1-pmenthen-9-ol
a very yield
unbranched
slightly
1,3-cycle-
[loo]. higher
has cyclo-
Hydroboration propor-
CH3CH2COCH2CH(CH3)2) alkyne,
CH3CZC-CH2CH2CH3
[lOl]_ Lithiation 1,3-dials
[102].
of
alkynes
followed
by
hydroboration-oxidation
provides
a synthesis
of
193 R-CH,-ECH
1.
BuLi
2.
BH3-THF
3.
NaOH-H202
,
L
R-CH-CH,CH,OH
Hydroboration
B2H6
2 .
Hydroxymethyl
and cryptands
of a C=CH2 group to CHCH20H [104, epoxides
diborane
normally
from trisubstituted
treatment
with
Studies This
without
such as lyields
to R2BH with
carbon-boron
and E-methylindene
diol
products
toward
achieving
LiA1H4 has been reported
more efficient
are
Disiamylborane terminal
synthetic
his work on autoxidation
and benzylic
reactions
evolve
hydrogen
Halogenation
on
of
[107].
Processes
has reviewed
ing trialkylboranes
bond formation,
[106].
section includes several more or less mechanistic
Davies
converts
by hydroboration-oxidation
105-J. opens epoxides
olefins
of Oxidative
them directed
radical
have been prepared
and oxidation
diborane,
RSB to REBX and reduction 3.
[103].
R
crown ethers
Although
has been reported
fi HOCH2$HP(OMe)2
CH&P(OMe)2 R
L
of alkenylphosphonates 1.
8
L
AH
also
boronic
of organometallic
acids,
to form peroxides
compounds,
includ-
Related
[lOS].
reviewed.
hydroboration olefins
investigations, most of
applications.
into
followed aldehydes
by pyridinium
chlorochromate
oxidation
[log]. Cr03-HCl-py
R-CH=CH2 + (Sia)$H The reaction a CIDNP study considered &Bu-OOH major
product
though
this
t-Bu-OOH
has shown.evidence
mechanism in their
(by GLC), reviewer
reagent
Pr3B with
R2B-O-fi-Bu
To end with the
of
RCH2CH0
[lli].- Oddly enough; the same research
a radical with
p>
+ RCH2CH2B(Sia)2
together
the
rapid
Pentane
mechanism
reaction was said
RB(OBu)OR,
to wager too many rubles
of to be a
and &-BuOH,
on it.
organoboranes
to alcohols
with
L-1131_
MoOPH
8H3-SMe2 > The use of described References
ICI
by Kabalka p_ 194
and Na0Ac.t.o
in
to have
results, Midland and Preston have shown that
(MoOPH) oxidizes
of configuration
of
[112].
RB(OBu)(-O-O-t-Bu),
of definitive
MoO6-pyridine-tMPA
study
in octane
with
would not care
a couple
complete retention
kinetic
(R =n-pentyl)
of a radical
group does not appear
convert
and Gooch [114].--Two
trialkylboranes of the three
to alkyl alkyl
iodides
has been
groups can be cleaved
194 highly
efficiently.
9%
e-e_
8s
e-e_,
Hydroboration
(-)-a-pinene which
of
followed
corresponds
by to
cis-2-butene
the
ICI treatment
displacement
with
BH3-THF R-CH=CH2
ICI.
p>
( RCH2CH2
with
13B
diisopinocampheylborane
yielded
from
&-(-)-2-iodobutane
having
inversion.
NaOAc
-
2 RCH2CH21
+ RCH2CH2B(OH)2
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50
BORON: BORANES IN ORGANIC SYNTHESIS ANNUAL SURVEY COVERING THE YEAR 1980* Cl. S. Matteson Department Pullman,
of Chemistry, Giashington
Washington
99164
State
University
(U-S-A)
CONTENTS INTROOlJCTION
166
B. BORANE REAGENTS
166
A.
2_ Mechanism and Theory
166 168
3.
Trialkylborohydrides
170
4.
Asymnett-ic
1.
Agents
Hydroborating
Hydroborations
170
and Reductions
C. CARBON-CARBONBOND FORMATION
172
1.
Homologation
2.
Alkenylborate
3.
Boron-Substituted
4.
Al lyl boron Compounds
182
5.
Enol- Borinates
186
6.
Boraadamantanes
187 189
via
Borate
172
Complexes
Rearrangements
176
Carbanions
181
D. HYDROBORATION-OXIDATION 1.
Natural
Products
2.
General
Synthetic
3.
Studies
189 190
Applications
of Oxidative
193
Processes
194
E. REFERENCES
-*Previous
survey,
: Relerences p_194
see 3.
Organometal
Chem.,
207 (1981)
13-65,
this
section
40-65.
166
A. INTRODUCTION The leading
contributor
to this
field
has continued
should
still
be fresh
Brown, whose i979 Nobel Prize whose tiork is cited
number and diversity
properties
and synthetic
of organic
utility
of hydroboration
but is rapidly
Herbert C.
memory.
Many of other1
in this survey are former students of Professor Brown.
increasing largely
to be Professor
in everyone’s
of organoboron
chemistry
expanding-to
compounds.
a more broadly
This field
the uniqus
once consisted
of the resulting
based variety
However, an'
to discover
trialkylboranesi
of organoboron
with the most general
in this reviews
survey but are cited
at the end of section
with the top i !
B-1.
8. BORANE REAGENTS
I. Hydroborating
Agents
Hydroboration search for highly
specific
conversion syntheses
is such a useful
new, more selective
Zweifel
compoun$
transformations.
Reviews have not been grouped separately to which they belong,
are beginning
and transformations
include
and wider range of synthetic
chemists
reaction
that considerable
hydroborating
agents.
effort
continues
Some are designed
ji :I .i ii I! on the ;i
to accomplish
$
objectivesand Pearson have reported
the preparation
to mixed thexyldiorganoboranes,
of thexylchloroborane
which are useful
intermediates
and its
;;
in ketone
:.
Cl]-
8Hp + HCl
Et20
)---I-
HH 8 ‘Cl
H$=CHR
R’Li or
1. NaCN
‘CH2CH2R -
B ‘Cl
>
R’MgX
2 . I
3. H202
0 II
RC H2CH2CR ’
An illustrative fir
tussock
application
of this
chemistry
was the synthesis
of the Douglas
moth sex pheromone. 1. CsH17CH=CH2
(CH2)9CH3
8HCl 2. C+-$l\C=C/(CH2)3M9C1
H’
‘H
')-I--
B’ ‘(CH 2 13>=C411 H’
\H
i
167
NaCN, PhCOCl,
H202
! CH3KH2)g-C-(CH2)3,C,C,CSHII
>
H’
Brown and coworkers tion
have prepared
of tetramethylethylene
regioselective
than
also
used
from
Zweifel’s
with
thexylchloroborane
for
in
approach
thexylchloroborane-methyl
H2BCl-SMe2,
thexylborane
‘H
and have found
hydroboration
a synthesis
of
sulfide the
of olefins
ketones
in the use of hydroboration
to
[2].
[3].
by hydrobora-
reagent
to be more
Brown’s
Note
that
introduce
the
this
last
group has differs
alkyl
group.
RCH=CH2 f
F-l-
B
H2BCl-We2
-
BHCl-SMe2
P
K+-HB( O-L-Pr)
‘CH2CH2R
R’CH=CH2
W,CO),O
H202,
-NaCN
3
FHZCHZR >
1,4-Oxathiane-borane
II ! I
than
is
dimethyl
B\
F-l-
OH-
CH$H2R
! RCH2CH2CCH2CH2R’
---
odoriferous
A
a new convenient
hydroborating
agent
[4].
It
is
less
sulfide-borane.
owS-BH3
‘The 1,4-oxathiane selectively
I$rialkylborane “xidizing
remaining
oxidized the
product sulfide
after
hydroborations
by hypochlorite
Conversely,
[S]. if
to water the
with soluble
its
borane
sulfoxide
trialkylborane
the medium is made sufficiently
complex without
can be oxidized
1
within
an hour.
In contrast,
HBBr2-SMe2 and HB12-We2
apidly and hydroborate olefins such as l-octene or cis-3-octene % The reagents are easily kefluxing CH2C12 without any catalyst. ciX3 to BH3-SW2. ith [
X3
dimethyl
The hydroboration
sulfide,
from which
products, the
free
the
without
basic.
! Brown and coworkers have reported that HBCl2-SMe3 hydroborates I _iively slowly, and requires an acid catalys t such as BC13 in order leaction
can be affecting
react
relathe
much more
within
a few hours
prepared
by adding
RBX2, form distillable
RBX2 may be obtained
olefins
to complete
in
complexes
by treatment
with
C61. Reaction hydrolyzed
of HBBr2-SMe2 with to boronic
acids
alkynes
or coupled
yields by the
alkenylboron
dibromides,
use of methylcopper
which may
to form symmetri-
168
-i-Pr
i-Pr-CXCH3
The useful yield
>
+ HBBr2-SMe2
hydroborating
by refluxing
agent
BH3-SMe2 with
Dicyclopentadienyltitanium lithium
alkylborohydrides
mixture
of
agents
is
g-alkyl-
Brown’s
The chemistry
c121.
reacts
with
of
>
'BBr2
produced
amount of
catalyzes
hydroboration
of
has been carried
Pmong the more exotic alkenes
quantitative
CC14 [8]-
the
Hydroboration
in nearly
or acetylenes
alkenes
out with
to a
hydroborating
at 80°C to form
[ll]_ has been republished
“Hydroboration,”
book,
c=c
an equimolar
by LiBH4 [9]_
which
3 CH3Cu
,CH3
BH2Cl-SMe2 is
dichloride
or 9-alkenyl-6-SB9H11
chemistry
H’
NaBH4 and SnCl4 in THF [lo]. 6-SB9Hll,
\
9-BBN has been reviewed
with
his
Nobel
Odom has reviewed
[13].
lecture
added
organoboron
[14].
2. Mechanism and Theory Significant both
additions
experimental
Structural
to our
and theoretical
characteristics
of
Wang and Brown have used boration
with
rate-limiting
knowledge
hydroborating infrared
is
the
the mechanism
agents
dissociation
are
spectroscopy
With reactive
9-BBN in CC14 [15]. step
of
of
hydroboration
from
of view have been made during the past year.
points
of
also
to follow olefins
(9-BBN)2
to
included the
in this
kinetics
section. of_ hydro-
such as cyclopentene,
the
2 9-BBN, and subsequent hydro-
boration of the olefin is rapid, resulting in kinetics first-order in (9-BBNJ2 and zero-order tion
in olef i n-
becomes
reversible,
order in olefin.
The kinetics l-butene.
With less resulting
reactive
olefins,
such
as cyclohexene.
the dissbcia-
in kinetics half-order in (9-BBN)* and first-
Olefins giving intermediate kinetics were also found.
of reaction
and cyclopentene
of 9-BBN with
1-hexene,
have been measured [16].
P-methyl-petitene,
3,3aimethyl-
169 Relative measured 4.49,
which
styrene,
rates
of hydroboration
by Vishwakarma corresponds
in accord with
more than
of substituted
to a slight. buildup the
idea
97% R-phenyiethanols
styrenes
A Hammett plot
and Fry [17]. that
the
of positive addition
by 9-BBN in THF have been
using
D* gave a value
charge
on the
is electrophilic-
of
p=
s-carbon
of the
The products are
cases.
in all
Calculations on the reaction of BH3 with C2H4 have been carried out at the 4-316 level, which represents substantial improvement in accuracy calculations of the
The mechanism involves
[18].
subsequent
rearrangement
n-complex,
rearrangement
which
of this
slightly
will
good agreement
Fehlner’s
sition
state
with
geometry
bring
the
experimental
is calculated
activation estimate
that
further
for refinement
energy down to 4 kcal/mol, in
(JOM 41 (1972)
to be a slightly
and its
energy for formation
of a few kcal/mol
It is expected
estimated
previous
of a n-complex
is no activation
and a barrier
exothermic,
complex to ethylborane-
of the calculations
formation
two steps, There
to ethylborane.
over
distorted
65-66).
The tran-
parallelogram.
transition state
a-complex
A semiempirical MO study of the mechanism of hydroboration has been published
c191.
Molecular orbital calculations on B2H6 have indicated
lation
is a major
contributing
factor
Brown and Wang have studied differing
steric
requirements
the
to the dissociation
that
energy
electron
corre-
[20].
association
of 9-BBN with a series of amines of 13C NMR [Ei]. The symmetry of the 9-BBN by the use of
system is diminished by complexing, and systems were found in which the amine complexes
either
did
at equilibrium,
dissociated
not dissociate,
or were not formed
detectably,
rapidly
and reversibly,
depending
on the
steric
amine.
+ NR3
knonequivalent
7
.?
equivalent
P
were not favored bulk
of the
170 derivatives typically show l3 C NMRspectra
9-Substituted-9-BBN
the 9-BBN group has the full stituent
9-BBN ring carbons, the
symmetry expected
on the boron introduces
two sides
[ZZ].
corresponding
and pyridine
complexes
indicating
The presence
diastereotopic
that
of a chiral
nonequivalence
subin the
of 9-R-9-BBN show nonequivalence between
of the 9-BBN unit.
3_ Trialkylborohydrides
Lithium triethylborohydride ing even lithium have reported chlorides, reagent
aluminum hydride
the
lactones,
groups [23-J,
for
reducing
quantitatively
powerful
in some respects.
epoxides,
tertiary
halides
to alkanes
agent,
surpass-
compounds, acid anhydrides
amides-to
Lithium triethylborohydride
alkyl
reducing
Brown, Kim, and Krishnamurthy
LiHBEt3 to reduce carbonyl
use-of
esters,
functional
is an exceptionally
[24].
alcohols,
and
and various
other
is a particularly
effective
Primary iodides
are reduced
in minutes at 25OC, bromides in a few hours.
Cyclohexyl
iodide
is 63%
reduced in 24 hr. Lithium trialkylborohydrides are readily formed by reaction with t_butyllithium as the hydride source [25]. R3B f (CH3j3CLi
The reaction
R3BH- Lit
+
proved successful
but also with hindered
+
of trialkylboranes
(CH3)2C=CH2
not only with the usual alkyl
and cycloalkyl
boranes such as P&Me-9-BBN, B-isopinocampheyl-9-BBN,
groups, and
thexyllimonylborane. The crystal
structure
sodium and hydride each hydride
of
(NaHBEt3)4-Et20 has been determined
hydrogen atoms occupy alternate
coordinated
to one boron and three
4_ Asymmetric Hydroborations
enantiomeric
excess
hydroborates
specificity, (e-e.)
The
of a distorted
cube.
with
sodium atoms.
and Reductions
Monoisopinocampheylborane high degree of chiral
corners
[26].
yielding
phenyl-substituted alcohols
after
tertiary
oxidation
olefins
[27]_
Ph 100% e.e
.H
Ph.,,, H--$ CH3.
-C+H
8l% e-e tH3
with a
having 81-100%
l-71
Ph\
AH3 c=c
CH3/
‘H
omeric
and
coworkers
=,t+acetylenic excesses
smaller
were
successful
have
ketones in
substituent
proved
82% e-e,
H +-C&H,
I+
+.__ H
cl-i;
Midland reduces
*OH
Ph-e,+
in
the
the
to
that
alcohols
range
l3-3-pinanyl-9-borabicyclo[3.3.l]nonane
with The
73-100%.
high
ketone
group
of
stereoselectivity
acetylenic
series of reactions.
this
with
reported
This
group asymmetric
RCOCZC02R’
Enanti-
[28]is
the
sterically
reduction
has
also
1291.
R ._ R --0
--*“*W R’csc-
i-D
6
ex
•t
v
Midland readily
and
available
diethylborane base and
and the
Preston by
or
oxidized
of
the
the
borane
to
mode of
alkyl
then the
z-3-hydroxy-l-octynyl
corresponding
allylic
migration
acetate,
ketone
rearranged
the
alcohol
[3O].
was &,
with product The
yielding
which
is
dipinanylborane, by treatment product
was
material
with with
all
having
excess.
yH R
OAc $ HCD-S-
hydroborated
dicyclohexylborane,
predominant
enantiomeric
have
reduction
R2BH >
C5Hll i
OH-
R2B\ /H H,C=C\CdOA~ H’+.C
H 5 11
R-B $’ H4
lCHH II H/CN C5Hll
Ho,;
“2O2
>
H&-.C/H II . H&
References p_ 194
H 5 11
trans., 50-74%
172 Factors
involved
been discussed
in chiral
from sodium borohydride, Stereoselectivities Directions
for
ketal
types
C-5, hydroboration
of a-pinene
synthesis
of asymmetric natural are covered
includes
alkyl(a-haloalkyl)borate
formation complexes,
and cyanidation Oxidative
acids
[32,33-J.
of the resulting
acid to form 3-pinamine
are
has been cited in sections
included
products
and control
carbonylations,
in ketone syntheses
rearrangements
promise of synthetic
condensations
have been
in section
B-3
C-l,
C-4, and
of relative
chirality
utility,
(sections
of organoborane boronic
esters
bonds by rearrangement and cyanidations.
have already
of alkyl(alkenyl)borate
of
Examples of
been cited
complexes,
in section covered
in
somewhat related. and together
These types of reactions with allylboron and enol
C-4 and C-5) constitute
chemistry
Matteson and Majumdar have reported to a-chloro
and cleavage
of carbon-carbon
C-2 and C-3, are mechanistically
borinate
prepared
via Borate Complexes
This section
applications
have
in part D-l.
Homologation
show great
with reagents
and carboxylic
of asymmetric trialkylborohydrides of asymmetric
CARBON-CARBON BONDFORMATION
sections
reactions
[34].
1.
B-l [1,3-j_
of glucose,
with hydroxylaminesulfonic
C.
carbonylation
have been accomplished
derivatives
Syntheses
The preparation
by hydroboration
of ketones
the hydroboration
in Organic
Other
and other
were in the range 12-64% e-e.
diisopinocampheylborane
[25].
in hydroboration
[31].
Asymmetric reductions
published
selectivity
to organic
the fastest-growing
field
of
synthesis.
the efficient
with dichloromethyllithium
homologation
of boronic
The process
[35].
esters
involves
the
same type of borate intrmediate as the reaction of RLi with C12CHB(OR*)2 to form R-CHCl-B(OR’)2, first reported by Rathke, Chao, and Wu [JOM 122 (1976) 145]_ However, starting
from RB(OR’)2 and C12CHLi opens up a variety
of new synthetic
possibilities. ,O-CR;
R-B i ‘O-CR’2
+
R = primary,
secondary,
/o
t-BuCH-B Cl ‘0
LiCHCl2 B
-I-
R
-100 “c
tertiary
PhS
25 Oc >
C12HC alkyl.
R-CH-B
I Cl
cycloalkyl,
/O
> t-Bu-CH-El, I 0 SPh
vinyl.
allyl,
benzyl;
and similar
R’ = H, CH3
displacements
R = Ph, Bu, cyclohej 3 Cl
173
H2C=CH-CH-6,
10
I
H2C=CH\ ,CH-B &-Bu02CCH2
LiCH2CO2-t=Bu
0
>
Cl H2C=CH\ ,CH-CH-B t-Bu02CCH2 I Ci
Bu-$H-6. PhCH20
LiCHC12
/O
Extension promising esters
of this
new type
was found
isomeric
purity,
utility
of this
isomers
of
thoroughly
,O
PhCH20
“
chemistry
of directed
except
where
characterized
=
Ph-B
Cl
chiral
>
by Cram for
esters
by Matteson Homologation
having
high
group was methyl by the
purity, his
[36].
esters
the migrating
Bu-:H-C,H-CHB PhCH20
synthesis boronic
in high
NaB03
’
was demonstrated
3--phenyl-2-butanol
CH3MgBr
to pinanediol
to give I-a-chloro
approach
3 ‘0
‘0
/O Bu-$H-C\H-B,
>
LiCHCl2
,O
synthesis studies
of
they
to a
(+)-pinanediol diastereo-
The potential
of both separate
chosen because
classical
and Ray has led
(83-97%)
(74%).
OH
diastereo-
had already
of nonclassical
been
ions.
Ph-B
CH3
CH3
CH3
CH3
1. BClB 2.
H20
, H 1
H (-)-pinanediol Ph +?(OHJ2 F CH3
Boronic esters
H f = -
-
ZH,
esters
in high yiel,ds
Referencesp.194
Ph+-B
M
IO> YoJ.-)
are
homologated
[37].
by Me3SiCHC1Li
to a-trimethylsilyl
Ph-g
tH3
-@OH T iH, H
boronic
174
Me3SiCHCl
+
/O R-CH-B &. ‘0 Me3 I
+Cl
R = c-Bu,
/O R-B ‘0
set-Bu, -
cyclopentyl,
* Me3SiCHCl
cyclohexyl,
P R-CH-B ‘0 I #Me3Si
->
R = CH3CH=CH-, CH2=CH-CH2-
Larson
and coworkers
borane
with
Me3SiCHBr + R3B
75-78 %
have found
homologation
intermediate,
that
trialkylboranes
of one of the &-alkyl
which may be oxidized
->
H202 NaOH
R-lH-8R2
+- R38
with
Me3SiCHBrLi
or
to form an a-silyl a-silyl
alcohol
[38].
R-$H-SiMe3 OH
H2°2 NaOH >
R-fH-BR2
+
react groups
to the corresponding
Me3Si
PhMe SiCHCl 2
x
PhCH2, PhSCH2
+
PhMe2SiCHClLi
77-87
R-FH-SiMe2Ph
PhMe2Si R = primary,
Two alkyl leading
secondary,
groups
or cycioalkyl
are transferred
to a synthesis
from R3B in the
of symmetrical
reaction
with
silyldialkylcarbinols
PhMe2SiCC12Li,
or ketones
[39].
2H202 PhMe2SiCC12 + R3B
,->
PhMe2Si-CR
cr207 PhMe2Si-CR , 2 -
NaOH ’
R-SC:
A simple reduction
homologation
has been reported CO, LiHAl(OMe)3
of 9-R-9-$BN by Brown,
to 9-RCH2-9-BBN Ford,
by way of carbonylation
and Hubbard [40].
Li Al H4
CH3S03H
R-B 3
R2C=0
OH
_20--
>
-
R-CH2-B =c):. _’
R = c-octyl. cyclopentyl.
cyclopentyl.
cyclohexy‘i.
cyclooctyl.
exo-2-norbornyi:trans-2methyl.._
.-..
and
175 KHB(O-i-Pr)3 ylation
has been found
of trialkylboranes
to be a superior
for
reductive
carbon-
c411.
+ CO + K+ -HB (O-i_+?-)
c.B<
reagent
3
->
H2o2 CHO
CH20H o-
has used the reaction of cyclic
Kabalka
to introduce
13C and l4 C labels
0-f
trialkylboranes ketone carbonyl
with KCN/(CF3CO)20 groups [42].
RBH2 >
II
I
into cyclic
R = thexyl
1.
K*CN
2.
( CF3CO)20,
3.
H202lNaOH
.
Hydroboration-cyanidation (*)-estrone
methyl
ether
has been used as a key step
in a total
synthesis
[43].
BH2 A
KCN -.(CF,W,O
H2°2
of
CH30
The conversion
of 9-BBN to bicyclo[3
CH30CHC12and Et3COLi followed Organic Syntheses 2. Al kenylborate the alkyl
control _ other
by oxidation
has been described
with in
in detail
Rearrangements react
electrophiles,
first followed
Examples have already
with various
groups,
and alkenyl
This section
generally
covers
electrophiles
by rearrangements
been cited
in sections
followed
_cyclopropanes
[45].
PMe CH2=C=C ‘Li
+
by rearrangement
or oxidizing
agents to
with a high degree of stereochemical
rearrangements
initiated
catalyzed
by protons,
iodine,
by transition
or
metals.
B-l [7] and B-4 [30].
A group led by Suzuki has found that reaction l-methoxyallene
by treatment
[44].
Alkyl(alkenyl)borates join
_3_l]nonan-g-one
of g-alkyl-9-BBN’s
with acetic
acid yields
with l-lithio-
l-alkyl-l-methoxy-
HOAc
R-B
>
>
,OMe HOAc B-CH2-CH=C, -> R
@-OAc
+ BT 63-7s
R = l-alkyl.
cycloalkyl,
Reactions has yielded
exo-norbornyl,
trans-2-trimethylsilyloxycyclohexyl
of anions from trisylhydrazones
vinyltrialkylborates,
l,l-dialkylethenes
of methyl ketones with trialkylboranes
which rearrange
on treatment
with iodine
to form
[46].
\ R;B CH2=C-R
>
R’3B-i=CH2
-.
177 7 ‘2
R;
>
R/C=CH2
l,l-Dialkylethenes organoboranes TiCl4/Ti
have been prepared
by treatment
(0-i-Pr)4
with
from 1,2-dimethoxyethenyllithium
C13CC02H followed
[47].
R3B
6uLi MeOC=CHOMe I Br
MeOC=CHOMe
5
Cl 3CC02H R3D--
I
R-F
MeOC=CHOMe
- CH20Me
NaOAc Ac20
R2C-CH20Me
TiC14
->
OHR2C=CH2
ri-
(can be oxidized
Yields
to
Isomeric
R2CHOHCH20Me) 2-Bu,
_1_pentyl.
Levy and coworkers olefins
.->
OMe
R-;-OMe
followed
>
R27
>
R =i-Bu,
and
by NaOAclAc20 and
cyclopentyl,
have found
by iodination
to provide
IL-hexyl,
that
45-78 x purity
89-100
%
cyclohexyl
9-alkyl-9-BBN
a stereocontrolled
reacts
with
synthesis
alkenyllithiums
of trisubstituted
[48].
/ C6H131C=C /”
f
R-B
>
3
‘Li
Et’
f ; ! 1
1
2
This
c=c’ ‘R
Et/
stereochemical
behavior during
H
‘6”131
;---+
outcome is
of trans-alkenylboranes the
12.and
NaOH, but hydroxide
-.
:.
on the
basis
by Suzoki’s
group [49].
with lead(IV)
of the
is not present
case.
of (1-halo-l-alkenyl)dialkylboranes
(AcOj21Ph h&e been studied Refe&ncesp.194
toward
in the present
iodination
Reactions
not what would have been expected
acetate
or
178 R2BH ->
BuCXBr
B”\
c=c
H’
Pb(OAc)4
,Br
8”, >
'BR2
H'
PhI(OAc)2
or
R = cyclohexyl,l,Z-dimethylpropyl
R’
B",
->
= primary
-n-hexyl,
alkyl
CH2Cl2
,Br
95-98
Yield
40-58%
B",
>
c=c
H'
,Br 'RI
%I
H’c=c’BR’;g;
96-97
Yield 0 Oc
Bu,
P-methylpentyl
54-65%
,R’ c=c
H’
%L
‘Br
90-96
Yield
R12BH ->
B”\
->
c=c
H’
R ‘+I-hexyl
Lithium methyl
'R
%Z -
n_octyl
BuECCl
,Br
Pb(OAc),
R'2BH BuEC-Br
c=c
/C ’
ketone
R3B-EC-Ph
the
B
CH2=CH-CCH3
+
0
in
presence
rearrangement of
titanium
TiC14
%
independent -Z isomer, of conditions
‘R’
l-alkynyltrialkylborates‘undergo
vinyl
35-55
tetrach?oride
and
Michael
addition
to
[50].
co1
-+
E
II R-C-fH-CH2CH2CCH3 Ph
R = alkyl;
similar
results
Alkenyldisiamylboranes Pd(PPh8)4
R-ECH
to
+
form
HB(Sia
and
alkenes
)2
with
B
ally1 or benzyl halides have been coupled with
[51].
R, H'
C/ 'B(Sia)2
-. :
..
179 CH2=CHCH2Br
R\
A
,H
HHC=C’CH2CH=CH
2
PdW’h,),
NaOH filkenyldialkylboranes molar
derived
amount of palladium
dialkylboranes
derived
of palladium
acetate
from terminal
acetate
from
acetylenes
and triethylamine
internal
acetylenes
are
rearranged
to form E-olefins are
cleaved
by an equi-
[52].
Alkenyl-
by even a catalytic
amount
to form -Z-olefins.
PhCXH + HB(Sia)2
Ph,
.->
Pd(OAc)2
/”
c=c
H/
Ph\
‘B(
Et3N
Sia),
’
c=c
H’
/” ‘Si
a
Pd(OAc)2 BuCZCBu
If
+
HBU
(cat.)
H’
‘B(Sia)2
THF
c=c
9-BBN is
coupled
Bu,
used
with
as
ally1
the
agent,
hydroborating
Bu,
c=c
H’ (solvent
the
internal
,Bu ‘H is proton
alkenylborane
source)
can
be
cross
and
cross
chloride.
Pd(OAc)2 (cat.) ““,r=c<,“”
+ CH2=CHCH2Cl
Bu ‘C& H/
p>
Bu ’ ‘CH2CH=CH2
3
Catechol coupled
with
alkeneboronic allylic
esters
bromides
have
in the
been
presence
treated
3CH3Li
R, ,H c=c ,o H’ ‘B
with
methyllithium
of CuI (533.
CH2=CHCH2Br
R
/H
‘CCC’ H’
‘CH2CH=CH2
‘0
R = alkyl,
Crotyl
Ph
bromide
89-97%
gave
complex condensation
R\ -H’
c=c
/H
a mixture
isomers
(46:52).
Propargyl
bromide
gave
more
HCXCH2Br
GUI
+4 -30
‘B
‘0 a
“c
’
:2=cc:,
--
40-55%
-. Referencesp.19k : .:
allylic
products. 3CH3Li
p
of
CH CHiC=CH 2
2
180 Yatagai copper
at
has found
-40
predominant reacted
to
similarly
to couple philic
-30
product
that
treatment
‘C followed (73-86%)
butyl
iodide
with
by allylic
is that
at 0 OC, with
cocatalyst
of dialkenylchloroboranes
the
halides
formed with
87-92%
allylic
yields
allylic
It
inversion.
or PhSLi.
Yields
3 mols of methyl-
1,4-dienes
[54]-
inversion.
organocopper.intetmediate
such as P(OEtJ3
with
was also
in the
found
possible
of a nucleo-
presence
were generally
The
Alkenyl-9-BBN
50-60%.
R R = H, Ph, CH3; X = Cl,
Hydroboration alkenylboranes
of acetylenes
with
and Brown to yield
obtained
by hydroborating
t-butyllithium,
the temperature tured
with
ally1
with
NaOCH3 followed
Campbell with
(major
Br
with
NaOCH3 followed
OC, the organocopper to form 1,4-dienes
intermediate
+ HB
VB
Bu “=‘<,.,
,H ‘BU
H’
BUEI
NaOCH3
+
r
La
BH 2
CuBr-SMe2
NaOCH3
CuBrSMe2 >
> ,-15
Oc
by CuBr-SMe2.
resulting by
By lowering
can be stabilized
in a stereospecific NaOCH3
Bu-CXH
of the
[55]. A -Z,Z-diene has been --E,E-dienes with dicyclohexylborane, reducing the iodide
I-iodohexyne
bromide
by reaction
by CuBr-SMe2 at 0 ‘C has been found
symmetrical
and treating to -15
9-BBN followed
isomer)
manner [56].
CuBr-SMe2
and cap-
Yamamoto and coworkers RCu-BF3 reagents high
ratios
pattern
(see
have published
allylic
of &attack
[57]
RCH=CH6R’$uf RBF$u+
with
halides,
a full
of R on the allylic
JOM, 180 (1979)
was noted,
and it
account
acetates, group,
regardless
Similarity
48).
was suggested
of the
and alcohols,
to the
that
the
of the
behavior
reaction
of
generally
give
substituent
of
may involve
as an intermediate. THF *b
IL-BuCu-BF3 + CH3CHAHCH2Cl
n-Bu, CH/CH-CH=CH2 3
Et20 &BuCu-BF3
(excess)
+ (CH3)+CHCH20H
(98% of product)
S”3 fi-Bu-C-CH=CH2
e-3
I
Dimesitylalkylboranes resulting
anions
are
deprotonated
have been methylated
by lithium with
dimethyl
MespBCH2-
_____)
(100% of product, 70% yield)
CH3
the
reactions
which
in THF and
dicyclohexylamide sulfate
[58].
(CH312S04 NLi 2
Mes2BCHg f
-3
CH
Mes2BCH2Ph
->
Mes2BCHPh
&
->
W
Mes,BL-ih ZH3
EH3 Mes = 2,4,6_trimethylphenyl
Pn efficient aldehydes,
homologation
of aldehydes.
R2CO to R2CHCH0, utilizes
RCHO to RCH2CH0, or of ketones
LiCH(i302C2H4)2
159-j.
R,
/H C=c, P B. 0 (not isolated) H’
NaB03
pHic i Referw+194. :
RCH;ICHO
.- :
,
to
182 Deprotonation lithium alkyl
halides
esters
of pinacol
trimethylsilylmethaneboronate
2,2,6,6_tetramethylpiperidide or condensed with
and.the aldehydes
has been accomplished
resulting
to yield
anion
has been alkylated
predominantly
with with
Z-alkeneboronic
[60]. LiTMP
p-
MeSi CH2B,
/o Me$iCHS,
>
0
O-i-
RCHO
R\ H’
SiMe Allylic
Bu3SnCl at the
,
‘H
70% cis
3
anions
are useful
S/O ‘0
GC’
+-
derived
l-position
from l-
or 2-alkenyl-9-SSN
to form almost
in erythro-selective
coupling
exclusively with
‘C&’ H’
or
derivatives,
which
Bu3Sn >
r\
H20
\SnSuS
p
>
‘H
Me3SiCl
[61].
)
cc
Pr
with
Z-allylmetal
aldehydes
-____-PrCH2CH=CHB
react
H2NCH2CH20H
C=C’ H’ ‘H
CH SnSu3 2
PhCHO
R Ph
‘r-J” OH
4.
Allylboron
compounds
The use of allylboronic
esters
by R. W. Hoffmann and coworkers. ceding
section
in stereocontrolled Related
chemistry
synthesis has just
has been developed
been cited
in the
pre;-
_ :
[61].
.-
:
_
,,
:
.’
.:
..
183
‘Hoffmann and Zeiss to achieve
chiral
have been used the
synthesis
of alcohols
allylboronic
useful
ester
in natural
reaction
products
with
synthesis
aldehydes [627.
Y cH31C=CA ” 0 H’ \8’ ‘0
=
C”3lC=C
Et+CHO <
1” N/I
H’
‘01
*
92% of product
8% of product
56% of product
44% of product
CH
I 3 ” - C,;++$C~ Transi.tion
state:
H I,,” _ __B,O 7*
R‘..^_+=o---A (derived
I and E_r-a’IkylthioalJylboronic
\O/
from cis
esters
boronic
react
ester)
highly
diastereoselectively
HO
-J+ I
R
SEt
with
184
RCHO EtS w
= z
Reaction
esters with aldehydes yields
of 1-butene-3-boronic
The -isomer L-homoallylic alcohols [64]. esters such as the pinacol ester are used. the a-methyl
substituent
into
BP ‘0
+
an axial
predominates Interference
conformation
if
mixtures
sterically
by the.pinacol
in the transition
Allyltrialkyltin esters
group forces state.
compounds react
-i-Bu,
with 2-chloro-1,3,2_dioxaborolane
Ph
to form allyl-
[65].
yQnBu3 + $1
SnBu3 + CIB,
-
y4y)‘,73x)
CH2Cl2
/O
W
boronic
RCHO p>
R = Me, i-Pr,
boronic
of g-and
hindered
>
0
P
WB\
0 (Slta)
+
/-7-8;;1
+ “0“) (10%)
(17%)
_.
:
-- -.
185
Reaction the borate threo-
of crotyllithium
complex
selective
with
followed
triethylborane
by reaction
condensation
with
or tributylborane
an aldehyde
results
to form in a highly
1663. PhCHO
+
BEt3
H 7
Carbon-13 allylic
NMR spectra
y-carbons
hyperconjugation
of allyltrialkylborate
and deshielding with
the
allylic
complexes
of the
a-carbons,
system
[67].
BR;
show shielding
an effect
consistent
of the with
C-B bond
BR3
Allyldialkylboranes
+H=CH-CH2BR2
-
BEt3-
Li+
l
EtO,
Fl C H’ ‘BR2
add to ethoxyacetylene
HCZC-OEt
+
fH3
$“3 CH,
3 trialkylborane-ethoxyacetylene
CH3
[68].
Bto\
C9H190H
C/CH\cH
H
2
adducts
can be converted
2
H
to allylacetylenes
[69].
Et3A1
I
HCZC-CH-CH=CH2
I
1
80-110.
tH3
ti BR2
‘ther ,examples loraadamantane .References p. 194
of related
chemistry: ---
: :.
..
allylborane
chemistry
are
included.in
section
C-6
on
186 5,
En01 Bori nates Boronic
esters
of enols
or dialkyl(alkenoxy)boranes
nized as being among the most useful sations,
which are useful
Evans and Taber synthesis 45-83%
in syntheses
have reported
of
the
isomer
are
intermediates of macrolide
the
The most favorable
[70].
content
of
for
becoming recogaldol
conden-
antibiotics.
use of chiral
boron enolates
case is illustrated.
corresponding
rapidly
stereodirected
Other
in directed
examples
to the one illustrated
chiral
ranged
as the major
from isomer-
(CH3)zCHCHO
--p-f-
\\ 0
-
?--
Ts
OBBu2
?+A
* Major
isomer Hirama
aldehydes
Minor
(> 97%) and Masamune have described
with
the
the &-and L-dialkylboron
0
(&SHg)$JOTf
II
CH3CH2C-S-t-Bu
0
OH
isomer
(< 3%)
Ts
stereoselective
enolates
enolate
of CH3CH2COS+3u
,OR(CgHg)2 C=C CH3’ ‘s-L-6u
of
[71].
RC”0 >
“1
______3 i-PrzNEt
condensation
R cos-t-Bu
s Hi
RCHO CH$H=C=O
+
j
Bu26S-t-Bu
-
COS-t-Bu
-
The preparation
of dibutylboron
These reagents react c721. to generate one regioisomer aldehydes
with
high
regio
with
and the
permits alkylation
alkylation are
and 9-BBN triflate
enolizable
of the enolate
ketones
in the
selectively,
has been described
presence
of tertiary
and the enolates
amines
condense with
and stereoselectivity.
Ho02 and Oudenes have found borinates
triflate
that
C73-J.
regiospecific.
addition Both the
of
LiOCH2CH2NMe2 to enol
reaction
used to form the enol
borinate
187
BBu2
9
0
RX
BuCH=C-CH3
BuCH-:-CHS
LiOCH2CH2NMe2
(from
N&HCOCH3
R = CH3,
d
and BBuS)
PhCH8, CH@HCH2,C2HS
Enol borinates readily
react
converted
regiospecif
with
PhSeCl at
-78
to a,s-unsaturated
‘C to form a-phenylselenyl
ketones
ketones,
The over-all
synthesis
which
are
is
ic.
‘jB(CH2R’ )2 R-C=CH-CH2R’ (from
[74].
+
PhSeCl
I:
p>
RCOCH=N2 + B(CH2R’ ),) 0
->
R-:-CH=CHR ’
Lithium potassium
enolates
enolates
from ketones
readily
fail
to react
with
form borate
complexes
[753.
6,
l
(CH&C-t=CH2
.-
Boraadamantanes This
field
has been created
trialkylboranes tane-like this
can be elaborated
structures
organoborane
having chemistry
discussed
in
by borane
carbonylation,
this
his work in this
review, field
A boraadamantane [77],
but the
-BR~K+ P (CH3)3C-C=CH2
O-K* R3B
trialkylboranes,
Carbonylation
by Mikhailov with
a tetracoordinate to synthesis
but
it
as well recently
does
in English
or acety’lenic boron at
a novel
cyclic
who discovered reagents
one apex.
is not as general
provide
as other
has been synthesized and oxidation
and coworkers,
allenic
route
compounds.
The applicability
as most of the other to adamantane Mikhailov
+
(CH3)2C=C=CH2
of topics
derivatives
has reviewed
[76]. from triallylborane
has yielded
the
and l,l-dimethylallene
corresponding
1-hydroxyadamantane. t
B(CH2CH=CH2)3
that
to form adaman-
s
w
.-. @
Triallylborane condenses with propargyl ethers [7&
2.5'C, RO-CH2CECH
i-
791.
ROCH2m,
130 'C_>
B(CH2CH=CH2)3 CH2C"=CH*
Triallylborane undergoes cyclization with l-methoxypropyne Cf301-
+
CH30C=CCH3
100
B(CH2CH=CH2)3
0;
140
crk$-Jq 3
Oc >
~H~CH=CH~
CH30H +
%
,,,g
&8(OCH3J2 3
Tris(2methylallyl)borane propargyl
HECCH20CH
ether
shows
140 3
+
similar
behavior
to
triallylborane
toward
methyl
[Sl].
WI2
-CH213 F
CH30H
Oc
-
CH20CH;
d
H3 I
THF BH3 THF
More details of boraadamantane synthesis have appeared [82]- The dimethylated boraadamantane derived irom the
THF and
pyridine
complexes
tricrotylborane [83].
and
MkOCH$XCH
has
been
synthesized
as
189 I_
L = THF or pyridine
I
Treatment of ination
lithium
I-alkyl-1-boraadamantanates
with cage opening
[84].
Bromination
with acetyl
[SS].
ing carbonylation
Several
reactions
and oxidation
results
in elim-
of 1-boraadamantane opens the ring to
form a bromomethyl compound, which can be hydrolyzed B-O derivative
chloride
with base to form a ring-expanded
of boraadamantane have been reported,
to form 1-adamantanol
includ-
[863.
D. HYDROBORATION-OXIDATION 1. Natural Products Hydroboration-oxidation alcohols. tions
This section
of natural
has been cited
covers
products. in previous
sponding amine in section pheromone in B-l [l]
has become a standard the use of this
process
for
synthesizing
in syntheses
and transforma-
Other hydroboration chemistry related to natural products sections, such as the conversion of a-pinene to the correB-4 [34]
or a steroid
and carbonylation in C-l
occuring
plant
of boranes
to make an insect
[43].
has been used in a synthesis
Rearrangement of a trialkylborane which is a naturally
procedure
growth regulator
of triacontanol,
[87-J.
WCl6, Cl 2C=CHCl CH3(CH2)13CH=CH2 F
BH3-THF CH3(CH2)13CH=CH(CH2)13CH3 B
CH3CN, Bu4Sn
Hz02
heat >
diglyme
CH3(CH2)28CH20H
OH-
Hydroboration-oxidation dien-3e-ol oxidation indole
of various
has been used in a steroid
alkaloid
tabersonine
borane as a means of controlling [92].
reactions
synthesis
states
[go].
stereochemical
leading
/ Refere-p-194 :
5a-cholesta-8,14[88]_
Hydroboration-
Hydroboration-oxidation Further
result
dienes
organoboranes.
between separated The utility
of
with thexyl-
from the geometric
of dihydromyoporone
of the
study of hydroboration
of nonconjugate relationships
(80-95~
to cyclic
was demonstrated in syntheses
chain.
example,
[89].
hydroboration
High stereoselectivities
ments of transition
for
has been reported
has been reported
coumarins has been reported [91]. Still and Darst have studied centers
steroids,
to 5&cholest-8-ene-3s.15a-diol.
chiral
requireof these
and the vitamin
E side
190 -- BH2
1.
&-J”
tt+
M 2.
+
H202, OH
OH
=
OH
\ Y,
OH
OH
2,
General
Synthetic
A variety process
are
Applications
of synthetic
sununarized
in this
Hydroboration-oxibation 1,4-diol.s
applications
and general
studies
of the
-
section. of bicyclohexenyls
hydrobor+tion-
ha& been’studies
as a’route
. to ch.iral’
[93]. ,_
(,
..
191
meso only Soderquist vinyl-,
and Brown have reported
propenyl-,
allyl-,
E941- Vinyltrimethylsilane BH3-THF, but 9-BBN yields 91% e-boryl
derivative
95% a-boryl
derivative
usual stereochemical
yields
mixtures
mainly s-boryl
rules
for
H'
isomer.
->
BH3-THF
yields the
CH3CH2$H-SiMe3 OH
of interest
has .been used in the synthesis
as a possible H202
.A_
cytidine
-. ..
of a 1,3_diaiepinone
deaminase inhibitor
H/N o=c B
Ft+ere-pi194
yields
HOCH2(iH-SiMe3
CO1
--
Hydroboration-oxidation
i
2-Propenyltrimethylsilane
C”3
/iMe =iH
derivative
with BH3-THFand 9-BBN
hydroboration.
co1
____3
of
of (L and e-boryl derivatives with
even with BH3-THF, and e-l-propenyltrimethylsilane functions follow with BH3-THF. More remote olefinic
CH3 CH3Lc
study of the hydroboration
and 3-buten-1-yltrimethylsilane
BH3-THF
H2C=Ij-SiMe3
a detailed
~.
[95].
192 Hydroboration-oxidation been
studied
reported
of
benzocycloalkenes
Hydroboration-oxidation
[96].
with
of
diborane
and
thexylborane
a bicyclo[4.l.O]heptene
has
has
been
[97].
d
B2H6
2.
H202
h
Hydroboration synthetic
1.
of
study
allylaziridines
and
vinylaziridines
has
been
reported
in
a
[98].
Ph
1-e B2H6
HOCH2CH2CH2 2.
‘T\j‘
N H
Ph PPh3 3 Br2
1_ 9-BBN
Ph CH2=CH
2. “\j-
N H
H 34 %
Hydroboration been
studied
pentadiene hexadiene of
of
L-991. to to
tion
of
does
and with
3_cyclopenten-l-al. 3-cyclohexen-l-al.
CH3CEC-CH2CH(CH3)2
than
cyclopentene
Hydroboration
attack
of
similar
with
boron
at
and
the
BH2Cl
limonene R2BH gives
3-position of
the
(to
to
followed
norbornadiene
various
hydroboration
norbornene
the
RBH2 and
R2BH stages
by oxidation
converts
to exo-dehydronorborneol, to
1-pmenthen-9-ol
a very yield
unbranched
slightly
1,3-cycle-
[loo]. higher
has cyclo-
Hydroboration propor-
CH3CH2COCH2CH(CH3)2) alkyne,
CH3CZC-CH2CH2CH3
[lOl]_ Lithiation 1,3-dials
[102].
of
alkynes
followed
by
hydroboration-oxidation
provides
a synthesis
of
193 R-CH,-ECH
1.
BuLi
2.
BH3-THF
3.
NaOH-H202
,
L
R-CH-CH,CH,OH
Hydroboration
B2H6
2 .
Hydroxymethyl
and cryptands
of a C=CH2 group to CHCH20H [104, epoxides
diborane
normally
from trisubstituted
treatment
with
Studies This
without
such as lyields
to R2BH with
carbon-boron
and E-methylindene
diol
products
toward
achieving
LiA1H4 has been reported
more efficient
are
Disiamylborane terminal
synthetic
his work on autoxidation
and benzylic
reactions
evolve
hydrogen
Halogenation
on
of
[107].
Processes
has reviewed
ing trialkylboranes
bond formation,
[106].
section includes several more or less mechanistic
Davies
converts
by hydroboration-oxidation
105-J. opens epoxides
olefins
of Oxidative
them directed
radical
have been prepared
and oxidation
diborane,
RSB to REBX and reduction 3.
[103].
R
crown ethers
Although
has been reported
fi HOCH2$HP(OMe)2
CH&P(OMe)2 R
L
of alkenylphosphonates 1.
8
L
AH
also
boronic
of organometallic
acids,
to form peroxides
compounds,
includ-
Related
[lOS].
reviewed.
hydroboration olefins
investigations, most of
applications.
into
followed aldehydes
by pyridinium
chlorochromate
oxidation
[log]. Cr03-HCl-py
R-CH=CH2 + (Sia)$H The reaction a CIDNP study considered &Bu-OOH major
product
though
this
t-Bu-OOH
has shown.evidence
mechanism in their
(by GLC), reviewer
reagent
Pr3B with
R2B-O-fi-Bu
To end with the
of
RCH2CH0
[lli].- Oddly enough; the same research
a radical with
p>
+ RCH2CH2B(Sia)2
together
the
rapid
Pentane
mechanism
reaction was said
RB(OBu)OR,
to wager too many rubles
of to be a
and &-BuOH,
on it.
organoboranes
to alcohols
with
L-1131_
MoOPH
8H3-SMe2 > The use of described References
ICI
by Kabalka p_ 194
and Na0Ac.t.o
in
to have
results, Midland and Preston have shown that
(MoOPH) oxidizes
of configuration
of
[112].
RB(OBu)(-O-O-t-Bu),
of definitive
MoO6-pyridine-tMPA
study
in octane
with
would not care
a couple
complete retention
kinetic
(R =n-pentyl)
of a radical
group does not appear
convert
and Gooch [114].--Two
trialkylboranes of the three
to alkyl alkyl
iodides
has been
groups can be cleaved
194 highly
efficiently.
9%
e-e_
8s
e-e_,
Hydroboration
(-)-a-pinene which
of
followed
corresponds
by to
cis-2-butene
the
ICI treatment
displacement
with
BH3-THF R-CH=CH2
ICI.
p>
( RCH2CH2
with
13B
diisopinocampheylborane
yielded
from
&-(-)-2-iodobutane
having
inversion.
NaOAc
-
2 RCH2CH21
+ RCH2CH2B(OH)2
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