1,2-diastereoselection induced by chiral silicon in the addition of Grignard reagents to acylsilanes

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Telrahedrcn Letters. Vol.32, No.46 pp6801-68W1991 Primed in Great Britain

1,2-DIASTEREOSELECTION

INDUCED

OF GRIGNARD

Bianca

F. Bonini,

Dipartimento

Stefano

di Chimica Viale

BY CHIRAL

REAGENTS

Masiero,

Organfca

Risorgimento

SILICON

IN THE ADDITION

TO ACYLSILANES

Germana

Mazzanti*,

#A. Mangini~, 4, 40136

and Paolo Zanf

Universfta

Bologna,

di Bologna

Italy

Sunsaary. The reactfon of acylsflanes 1 with Grignard reagents gives the dfastereomeric a-hydroxysilanes 3. The level of asymmetric induction depends on the nature of R’ and R*. Good

results

were

obtained

for

desilylation

occurs

The addition

of organometallic

Interest

particularly

Recently

Ohno

exceptional reagents;

et

These results

fluorfde

giving

suggested

that,

reported

hydrogen

The

the

has already

at silicon

with

as~rnetr~~

Induction.

at

silicon

desilylation of chiral

good results

only

the substitution a different acylsilanes

in principle,

based

on

silicon

been exploited and

by us

with

these

wfth

Grignard

was tested

with

fnducing

during

results

reagents

obtained.

as

bearing

an a-chfral

carbon

addition

from

were

the

at silicon

towards

concerning as

In the majority

the the

at silicon

On this

by replaclng

basis

with

of

an

gave

by means

of

synthesis

of

"asymmetric"

good

we decided

3-10

to study

group with

chtral

levels

of

of acylsflanes

the inducing group

at Co.

the potential

removed

reaction

of cases

the a-naphthyl

chiral

stereochemfstry

the methyl-phenyl-a-naphthylsilyl

in very few instances.

stereospeciffcally

of thioa~ylsilanes which

show

organometa~lic

the asymmetric

the reactfon reagents,

of

aldehyde

as equivalents

well

of great

products.'

group can be easily

auxilfarfes 314

is a topic

of natural

chiral

an approach

Subsequent

synthesis

reactions

derived

R?=Ph.

at carbon.

compounds

nu~leophilic

in

organometallic

here our preliminary

pattern

in

formally

the chira?

of a-hydroxysilanes

sflicon

acylsilanes

obtained

R'=d-Napht,

carbonyl

us to start with acylsilanes

1,3-dienes

We wish to report

that

alcohols

in this case,

approach

to chiral

selectivity

ion, thus allowing,

alcohols.

chfral

a1.2

and

of configuration

in the stereoselective

a-hydroxysflanes

protiodesilylated

advantage

as a tool

Rz=Me

inversion

reagents

diastereofacial the

R'=t-Bu,

with predominant

of

the

potential

, whfch gave

the effect groups

of

exertfng

steric hindrance, like n-butyl and t-butyl. Wfth this aim in mfnd, we prepared 11 12 la-f using the dfthiane route proposed by Brook ; the dfthfane precursors

6801

6802

Za-f, when racemic, a THF solution derivative dithlane Sommer's

were

obtained

in a one-pot

of dfchloromethylphenylsilane

R'Li

and

subsequently

with

reaction ffrstly

1 equiv.

of

by treating,

with the

1 equfv.

at -20°C of

lithiodithiane

2f was prepared from SC-I-methyl-a-naphthyl-phenyl-chlorosilane 14 method (Scheme 1).

the 13

under

organolfthfum

. The homochiral

obtafned

Scheme 1

R’U __)

PhMeSIC12

PhMaR’SlCl

-

s

U 2

HgC12/CdC03 +

G&l h

0

a:R*=Me.R'=

1 a-f

n-k

b:R* = Me, R’= t-Bu c:R*= Me, R' = a-Np

Ph.R'= e:!?= Ph.R'= f:F?= Ph,R'=

d:R2=

Scheme 2

l’&gX -80

/

Et20 Oc

)

NH,+CI sat. w -80 Oc

1 a-f

Tablel. Reactionsofl

3 a-c

with F?MgBr16 dliaslereoisomer

ElllIy

F?

yield %

d.e. %”

I ratio’5

I

Ph

97

16

2

Ph

60

72

3

Ph

63

44

4

Me

98

9

5

Me

63

19

6

Me

98

79’8

1.411

6.1:l

2.c:l

1:1.2 lA.5

1:&5

argon,

n-Bu I-Bu a-Np

with the

6803

Acylsilanes a constant

1 were

temperature

in a-hydroxysilanes

substitution

group and

that of

pattern

only

Id in

A

work.

substituents

4).

in

and organometallic

In order

to verify

a-hydroxysilanes silicon

the general

reaction, THF,

which

gave

methanol)

in

85%

with

Surprisingly

predominant

the

diastereomeric the major which

enantiomeric

excess

enantiomer

would

have

follows

that

process

and that

bearing

in

the

the

present

is highly

results

Acknowledgment.

of

case

la (entry

but

this

results

interchange

stage of

1, entries

bearing

1)

chiral

preliminary

(Table

compounds

the

21,

of the asymmetric

=

the

the 1 and

synthesis,

chiral

on

as

a-carbon

28%)

of MeMgBr

fluoride

=

to that

From

protiodesilylation

much

starting

not

results a

=

The

DMF

4.7,

than

material (note

19

the

at carbon

18

or

36:64).

described

highly

18

tc

lower

diastereoisomer

the

is

R/S

configuration

of the

predominant

R-phenylethanol).

be

we performed

-12.5"

(

of

asymmetric

in either

[aID

to

the absolute

fs opposite the

found

of

on R(+)-lf.

(TBAF)

(S)-configuration was

desilylation

of alcohols,

1-phenylethanol the

the

possibility

synthesis

by addltion

3c. Moreover

for

resultsl

establish

active

(e.e.

C(S)

the

By

n-butyl

5). These

at this

reagent

Ohno's

to

having

1-phenylethanol

silyl

on the structure

These

carbonyl

(entry

(entry

progress.

the

by

of 3c,

that

above

it

stereoselective

it proceeds

a-hydroxysilanes depend

optically

excess

produced

MeMgBr

in the direction

tetrabutylammonium

with

Sl(R)

in

In the asymmetric

of the starting of

by

increases

PhMgBr

to rationalize is

herewith

enantiomer

has the configuration

retention

atom

the

is affected

the a-naphthyl

with

of le with

applicability

auxiliary

performed yield

reaction

t-butyl

lb

of 3c (d.e. = 79%) obtained

was

of the

resulting

1).

group

the

and the Grignard

between

and in conjunction

the protiodesilylation

2, Table

at

17

reagents.

to act as a chiral

(Scheme

of

ether

steps,

by

investigation

reactions

quenching

of both acetyl

reaction

is a reversal

in diethyl

in the reactions

are difficult

extensive

cross

yields

acetylsilane

R* and R3 at the acylsilane

observed

groups

of

in the cross

4, 2 and 5, 3 and 61, there often

induction

reagent

and the

replacement

i.e.

Replacement

in nature,

more

addition

that the diastereoselectivity

reaction

seem contradictory

the

of Grignard

in good to quantftative

(entry

the

an excess

for both

the chiral

It drastically

our

with

at silicon,

lowers

benzoylsilane

decreases

15

1 indicate

drastically

induction

of -80°C

3a-c

The data of Table the

then reacted

with predominant inversion of configuration at the carbon 18 group. Ohno's statement2 that the protiodesilylation of sterespecific

is certainly

not

generally

valid

but

seems

to

of the substrate.

set a limit to the use of asymmetric

The authors

wish

to thank

Prof.

silicon

B. Zwanenburg

as chiral

(Nijmegen,

auxiliary.

NL) for helpful

6804

dlscusslons. References 1. 2. 3.

and notes

P.A. Bartlett, Tetrahedron 1980, 36. 3. M. Nakada, Y. Urano, S. Kobayashi, M. Ohno, J.Am.Chem.Soc., B.F. Bonini,

G. Mazzantl,

P. Zanl and G. Maccagnanl,

1988, 110, 4826.

J.Chem.Soc.,

Chem.Commun.,

1988,

365. 4.

B.F. Bonlnl,

G. Maccagnanl,

S. Masiero,

G. Mazzantl

and P. Zanl,

Tetrahedron

Lett.,

1989, 30, 2677. 5.

R.G. Daniels

6. 7. 8. 9.

S.J. Hathaway

and L.A. Paquette,

Organometallics,

and L.A. Paquette,

1982, 1, 1449.

J.Org.Chem.,

1983, 48, 3351.

J.L. Fry and M.G..:AdlIngton, J.Am.Chem.Soc., J.L. Fry and M.A. McAdam, Tetrahedron Lett., G.L. Larson and E. Torres, J.Organomet.Chem.,

1978, 100, 7641. 1984, 5859. 1985, 293, 19.

1988, 53, 10. G.L. Larson, V. Cruz de Maldonado, L.M. Fuentes, L.E. Torres, J.Org.Chem., 633. 11. la: b (CDCl,) 0.47 (s, 3H, SlMe), 0.63-1.63 tm, 9H, n-Bu), 2.23 (5, 3H, COMe), 7.23-7.77 (m, 5H, Ph) ppm; m/e 220 (M+); yap, (CCl,) 1640 cm-' (CO). 1b:d (COCl,) 0.57 (s, 3H, SlMe), 1.00 ts, 9H, t-Bu), 2.30 (s, 3H, COMe), 7.30-7.93 (m, 5ti. Ph) ppm; m/e lc: 6(CDCl,I 0.87 (s, 3H, SiMe), 2.27 (s, 3H, 220 CM+); Y,lx (neat) 1640 cm-'(CO). tOMe), 7.07-8.07 (m, 12 H, aroml ppm; m/e 290 (M+); (neat.) 1635 cm-' (CO). Id: 7.30-7.80 Cm, lOH, GCCDCl,) 0.62 (s, 3H, SiMe), 0.85 and 1.10-1.43 (t, a~,~b?, n-Bu), arom) ppm; m/e 282 CM+); Y_ (neat) 1610 cm-' (CO). le: d(CDCl,) 0.60 (s, 3H, SiMe) 1.03 (s, 9H, t-Bu),

7.13-7.77

Cm, lOH, arom) ppm; m/e 282 (M+);

vmax (neat)

1610 cm-'

(CO). If: see ref. 12 1967, 89, 431. 12. A.G. Brook, J.M. Duff, P.F. Jones and N.R. Davis, J.Am.Chem.Soc., 1975, 40, 231. 13. D. Seebach, E.J. Corey, J.Org.Chem., 1964, 86, 3271. 14. L.H. Sommer, C.L. Frye, G.A. Parker and K.W. Michael, J.Am.Chem.Soc., as a mixture cf the two diastereolsomers whose ratio 15. Compounds 3a-c were characterized at was determined by 'H NMR analysis at 200 MHz (Si-Me proton signals resonating lower field vs. those resonating at hlgher field). 3aa(CC14) 0.17 and 0.23 (2s, 3H, SlMe), 0.51-11.47 (m, 9H, n-Bu), 1.53 (s, 3H, Me), 2.0 (s, lH, OH), 6.8-7.6 (m, lOH, arom) ppm; m(e 298 (M+); y,,, (Ccl,+) 3550 cm-' (OH). 3b: b CC,D,) 0.24 and 0.27 (2s. 3H, SiMel, 0.94 and 1.05 (2s, 9H, t-Bu), 1.36 and 1.49 (2s, 3H, Me), 2.08 (s, lH, OH), 6.9-7.3 (m, lOH, arom.) ppm; m/e 298 CM+); v_x (Ccl,) 3550 cm-' (OH). 3c: 6 (CDCl,) 0.65 and 0.72 (2s, 3H, SiMe), 1.65 (s, lH, OH), 1.78 and 1.83 (25, 3H, Me), 7.0-8.0 Cm, 17 H, arom) ppm; m/e 368 CM+); v,,x(CC14) 3550 cm-' (OH). 16. Ail reactlons were performed on racemic 1, except the one reported in entry 6, Table 1, and were repeated at least twice. 17. J.D. Morrison, H.S. Mosher, Asymmetric Washington D.C., 1976.

Organic

Reactions,.

Ed.

Am.Chem.Soc.,

was also performed by A.G. Brook (Acc.Chem.Res. 1974, 7, 77) to 18. This reaction establish the stereochemfstry of the base promoted sllylcarbinol to silylether rearrangement where Inversion of conflguratlon at carbon was found. The absolute conflguratlon of the major dlastereoisomer was determfned to be Si(R)C(S). 19. The reaction

was repeated

basis of the [a],

(Received

value

in UK 17 September

three times

In both solvents.

of RC+)-1-phenylethanol

1991)

The e.e. was determined

(+45"; c 5, methanol).

on the