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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
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