Preparation of chlorosilyl enolates

Article abstract of DOI:10.1021/jo981740h

A variety of chlorosilyl enolates has been prepared starting from esters, thiol esters, acylsilanes, and ketones. Two general methods are involved, direct enolsilylation with trichlorosilyl triflate and diisopropylethylamine, and a number of methods based on electrophilic substitution of either C- or O-silyl or stannyl carbonyl compounds. The most useful method is a Hg(OAc)₂-catalyzed transsilylation from trimethylsilyl to trichlorosilyl enol ethers, providing a wide range of ketone enolates in good to high yield.

Full text of DOI:10.1021/jo981740h

J . Org. Chem. 1998, 63, 9517-9523
9517
P r ep a r a tion of Ch lor osilyl En ola tes†
Scott E. Denmark,* Robert A. Stavenger, Stephen B. D. Winter, Ken-Tsung Wong, and
Paul A. Barsanti
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801
Received August 25, 1998
A variety of chlorosilyl enolates has been prepared starting from esters, thiol esters, acylsilanes,
and ketones. Two general methods are involved, direct enolsilylation with trichlorosilyl triflate
and diisopropylethylamine, and a number of methods based on electrophilic substitution of either
C- or O-silyl or stannyl carbonyl compounds. The most useful method is a Hg(OAc)2-catalyzed trans-
silylation from trimethylsilyl to trichlorosilyl enol ethers, providing a wide range of ketone enolates
in good to high yield.
Ta ble 1. Syn th esis of Aceta te Ch lor osilyl En ola tes by
th e Sta n n a n e Meth od
In tr od u ction
Recent reports from these laboratories have described
the chemistry of a new class of aldolization reagents
based on electron-deficient silyl enolates.1 These species
exhibit remarkable reactivity patterns, spontaneously
reacting with aldehydes at or below ambient tempera-
ture. More importantly, these reactions are accelerated
by the addition of catalytic quantities of Lewis bases
(chiral phosphoramides). When cyclic enolates are used,
aldol adducts are formed with high syn-diastereoselec-
tivity in the uncatalyzed reactions, suggestive of a closed,
boatlike transition structure.1b,e In contrast, reactions
catalyzed by chiral phosphoramides typically provide
products resulting from closed, chairlike transition struc-
tures, often with good to excellent enantioselectivity.1b,e
Although several chlorosilyl enolates were known2,3 when
our work commenced, new, more efficient methods of
synthesis were needed to provide access to certain classes
of enolates and to enhance the general utility of this aldol
reaction. We describe herein general methods for the
synthesis of these unique and useful reagents.
entry
silane
HSiCl3
R1
R2
Cl
Cl
Cl
Cl
Me
product
yield,a
%
1
2
3
4
5
6
H
Cl
Me
Ph
Me
2a
2b
2c
2d
2e
2f
48
65
57
23
18
19
SiCl4
MeSiCl3
PhSiCl3
Me2SiCl2
(CH2)3SiCl2
-(CH2)3-
a
Yield of distilled product.
literature were those derived from methyl acetate, pre-
pared by the metathesis of alkyl (trialkyl)stannyl acetates
with chlorosilanes.2 We have also found this to be the
most general procedure for the generation of such acetate-
derived chlorosilyl enolates. Treatment of methyl (tribu-
tylstannyl)acetate (1)4 with an excess of the appropriate
chlorosilane at 0-25 °C led to the formation of the
chlorosilyl enolates 2, Table 1. Excess chlorosilane was
typically used to control the quantity of bis(enoxy)chlo-
rosilane byproducts formed by reaction of the primary
chlorosilyl enolate with starting stannyl acetate. When
the reaction was complete, excess chlorosilane was
removed and the products were distilled at 0-25 °C
under reduced pressure. These manipulations must be
carried out at the lowest possible temperature, as the
chlorosilyl enolates 2 are unstable with respect to their
C-silyl isomers and isomerization occurs rapidly at 70-
90 °C.2d These C-(chlorosilyl) esters are inert in the
subsequent aldol reactions and do not revert back to the
O-bound trichlorosilyl enolates under common reaction
conditions.
Although the reaction proved to be general for the
synthesis of various chlorosilyl enolates1c the yields of the
process were moderate at best. The lower yields of
enolates in entries 4-6 (Table 1) reflect the lower
volatility of these enolates and the greater difficulty in
separating them from Bu3SnCl and from the C-(chlorosi-
lyl) isomers. That these substances are O-bound silyl
enolates (enoxychlorosilanes) was readily confirmed by
examination of the 1H NMR spectrum of trichlorosilyl
Resu lts
En ola tes Der ived fr om Ester s a n d Ester -Su r -
r oga t es. The first chlorosilyl enolates reported in the
† The Chemistry of Chlorosilyl Enolates. 9.
(1) (a) Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T. J . Am.
Chem. Soc. 1996, 118, 7404. (b) Denmark, S. E.; Wong, K.-T.;
Stavenger, R. A. J . Am. Chem. Soc. 1997, 119, 2333. (c) Denmark, S.
E.; Winter, S. B. D Synlett 1997, 1087. (d) Denmark, S. E.; Stavenger,
R. A.; Wong, K. T. J . Org. Chem. 1998, 63, 918. (e) Denmark, S. E.;
Stavenger, R. A.; Wong, K.-T. Tetrahedron 1998, 54, 10389. (f)
Denmark, S. E.; Stavenger, R. A. J . Org. Chem. 1998, 63, 9524.
(2) (a) Burlachenko, G. S.; Khasapov, B. N.; Petrovskaya, L. I.;
Baukov, Yu. I.; Lutsenko, I. F. J . Gen. Chem. USSR (Engl. Transl.)
1966, 36, 532. (b) Lutsenko, I. F.; Baukov, Yu. I.; Burlachenko, G. S.;
Khasapov, B. N. J . Organomet. Chem. 1966, 5, 20. (c) Burlachenko,
G. S.; Baukov, Yu. I.; Dzherayan, T. G.; Lutsenko, I. F. J . Gen. Chem.
USSR (Engl. Transl.) 1975, 45, 73. (d) Buakov, Yu. I.; Lutsenko, I. F.;
Moscow University Chem. Bull. (Engl. Transl.) 1970, 25, 72. (e)
Ponomarev, S. V.; Baukov, Yu. I.; Dudukina, O. V.; Petrosyan, I. V.;
Petrovskaya, L. I. J . Gen. Chem. USSR (Engl. Transl.) 1967, 37, 2092.
(f) Burlachenko, G. S.; Baukov, Yu. I.; Lutsenko, I. F. J . Gen. Chem.
USSR (Engl. Transl.) 1970, 40, 88.
(3) (a) Benkeser, R. A.; Smith, W. E. J . Am. Chem. Soc. 1968, 90,
5307. (b) Walkup, R. D. Tetrahedron Lett. 1987, 28, 511. (c) Walkup,
R. D.; Obeyesekere, N. U. J . Org. Chem. 1988, 53, 920. (d) Walkup, R.
D.; Obeyesekere, N. U.; Kane, R. R. Chem. Lett. 1990, 1055. (e) Kaye,
P. T.; Learmonth, R. A.; Ravindran, S. S. Synth. Commun. 1993, 23,
437. (f) Shea, K. J .; Zandi, K. S.; Staab, A. J .; Carr, R. Tetrahedron
Lett. 1990, 31, 5885. (g) Gillard, J . W.; Fortin, R.; Grimm, E. L.;
Maillard, M.; Tjepkema, M.; Bernstein, M. A.; Glaser, R. Tetrahedron
Lett. 1991, 32, 1145.
(4) Zapata, A.; Acun˜a, A. C. Synth. Commun. 1984, 14, 27.
10.1021/jo981740h CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/24/1998

9518 J . Org. Chem., Vol. 63, No. 25, 1998
Denmark et al.
Sch em e 1
Sch em e 2
enolate 2b, which was contaminated with a small amount
of the C-silyl isomer.5 The spectrum of the enolate (O-
silyl) displayed two doublets at δ 3.41 and δ 3.65 ppm (1
H each) and a singlet at δ 3.65 ppm (3 H), whereas the
C-(trichlorosilyl)acetate displayed two singlets at δ 3.75
ppm (3 H) and δ 2.78 ppm (2 H). Similar procedures using
various alkyl (tributylstannyl)propanoates and SiCl4 led
to complex mixtures, with the dominant products being
the C-(trichlorosilyl)propanoate derivatives.
Sch em e 3
To avoid the use of tin compounds in stoichiometric
amounts, other routes to chlorosilyl enolates were inves-
tigated. A conceptually similar process can be envisioned
that employs an alkylsilane as the electrofugal group.
Unfortunately, combination of SiCl4 with various alkyl
C-(trimethylsilyl) esters led to no reaction. However,
when trichlorosilyl triflate6 was used as the trichlorosi-
lylating reagent, relatively clean conversion to the trichlo-
rosilyl enolate was observed, Scheme 1. Treatment of
methyl C-(trimethylsilyl)acetate (3) with trichlorosilyl
triflate in CDCl3 at room temperature led to fast (<10
min) conversion to the O-(trichlorosilyl) enolate 2b. The
bulky ester enolate 57 was synthesized by treatment of
the silane 4 with trichlorosilyl triflate at room temper-
ature though here conversion was slow, requiring over
30 h for completion. The enolate 5 (assumed to be of E
configuration7) could be obtained in reasonably pure form
(1H and 19F NMR analysis) in essentially quantitative
yield by simple treatment of 4 with trichlorosilyl triflate
followed by removal of the byproduct TMSOTf under
reduced pressure.
The extreme reactivity of trichlorosilyl triflate also
proved useful in the direct enolsilylation of carbonyl
compounds. Initial experiments revealed that esters and
ketones were inert to the action of SiCl4 and a variety of
amine bases. Furthermore, reaction of chlorosilanes with
alkali metal enolates proved ineffective. However, when
trichlorosilyl triflate was used in conjunction with
i-Pr2NEt, rapid conversion to the trichlorosilyl enolates
was accomplished for ketones, cyclic esters, and thiol
esters. Acyclic esters reacted very slowly under these
conditions and led only to poor conversion to the C-
(trichlorosilyl) esters. Amides were inert, and acyl ox-
azolidinones provided complex mixtures of products.
Other tertiary amine bases (Proton Sponge, pentameth-
ylpiperidine, Et3N, Me2NEt) seemed to offer no advan-
tage, and pyridine and its derivatives were wholly
ineffective in this transformation. Although the reaction
proceeded well in chlorinated solvents, difficulties in-
volved in the isolation of the chlorosilyl enolates led to
the use of pentane as solvent, so that the majority of the
amine salts could be removed by Schlenk filtration. Thus,
trichlorosilyl enolates 6 and 7 were obtained after distil-
lation in modest yield directly from the corresponding
carbonyl compounds. This method was also found to be
effective for acylsilanes, Scheme 2. Treatment of 88 under
the standard conditions led to the formation of the
enolate 9 as a 9/1 mixture of Z/E isomers (assignment of
configuration tentative) in 44% yield.
En ola tes Der ived fr om Keton es. Ketone-derived
chlorosilyl enolates have also been prepared previously.
For example, the acetone enolate 10a was generated by
a reductive chlorosilylation reaction reported by Ben-
keser,3 Scheme 3. We were able to reproduce the Ben-
keser procedure, i.e., treatment of chloroacetone with
trichlorosilane and Bu3N to prepare the trichlorosilyl
enolate 10a . Curiously, Et3N and i-Pr2NEt seemed un-
able to effect this transformation. In addition, in our
hands the use of pentane was found to be superior to THF
(the solvent used in the Benkeser report), providing
cleaner reaction and allowing easier separation of the
solvent from the volatile chlorosilyl enolate. The enolate
10a could be purified reproducibly by vacuum-transfer
of the reaction mixture away from the ammonium salts,
concentration of the crude distillate, and redistillation
of the residue. However, due to the necessity of this
vacuum-transfer step, only relatively volatile enolates are
(5) All acetate enolates in this study were contaminated with small
quantities of the corresponding C-silyl isomer. Complete removal is
neither necessary, nor practical, as the O-silyl enolate does isomerize
slowly, even when stored at -20 °C.
(6) (a) Bassindale, A. R.; Stout, T. J . Organomet. Chem. 1984, 271,
C1. (b) Ru¨dinger, C.; Beruda, H.; Schmidbaur, H. Z. Naturforsch. B
1994, 49b, 1348.
(7) The corresponding lithium enolate has been used in aldol
reactions by Heathcock, see: (a) Heathcock, C. H.; Young, S. D.; Hagen,
J . P.; Pirrung, M. C.; White, C. T.; VanDerveer, D. J . Org. Chem. 1980,
45, 3846. (b) Heathcock, C. H.; Pirrung, M. C.; Montgomery, S. H,
Lampe, J . Tetrahedron 1981, 37, 4087.
(8) Fujiwara, T.; Sawabe, K.; Takeda, T. Tetrahedron 1997, 53, 8349.

Preparation of Chlorosilyl Enolates
J . Org. Chem., Vol. 63, No. 25, 1998 9519
Ta ble 2. Syn th esis of Keton e Tr ich lor osilyl En ola tes by
th e Sta n n a n e Meth od
Sch em e 4
entry
stannane
R1
R2
enolate
yield,a
%
1
2
3
4
5
6
11b
11c
11d
11e
11f
11g
t-Bu
Ph
Ph
-(CH2)3-
-(CH2)4-
-(CH2)5-
H
H
Me
10b
10c
10d b
10e
10f
54
67
83
27
78
63
The most general method yet discovered for the syn-
thesis of chlorosilyl enolates of ketones is an interesting
trans-silylation catalyzed by soft, electrophilic metal
salts, especially Hg(OAc)2. It was known that treatment
of C-mercurioesters2b or stannylated esters2a with ha-
losilanes provided mixtures of the C-silylesters and
O-silyl esters. In addition, C-mercurioketones11 and C-
(trichlorostannyl)ketones12 were known to be formed
cleanly from TMS enol ethers and the corresponding
metal salts. We therefore reasoned that a Lewis acidic
species could function as a catalyst for the trans-silylation
from alkylsilyl to chlorosilyl enol ethers. Initial studies
using 1 equiv of SiCl4 and 10 mol % of TiCl4, BF3‚OEt2,
or SnCl4 were not encouraging; only SnCl4 seemed to
promote reaction with the TMS enol ether of pinacolone
(12b), and this proved to be neither general nor amenable
to large-scale reactions. However, when softer Lewis
acids such as Hg(OAc)2, Hg(OTFA)2, Tl(OTFA)3, and
Pd(OAc)2 were used at 5 mol % loading, clean conversion
to the trichlorosilyl enolate was observed.
The TMS enol ether derived from methyl isopropyl
ketone (12h ) was used as a test substrate to examine
several reaction parameters. Curiously, although a slight
excess (2-3 equiv) of SiCl4 did help reduce the amount
of bis(enoxy)dichlorosilane formed, larger excesses (5
equiv) slowed the reaction dramatically. In addition,
conducting the reaction at concentrations higher than 1
M led to significant reduction in overall rate. In general,
all of the salts behaved similarly, though Tl(OTFA)3 was
slower than the others, and when Pd(OAc)2 was used
with cyclic ketone substrates, poor conversion was noted,
along with formation of a palladium mirror on the
reaction vessel. From these studies it was determined
that 5 mol % loading of Hg(OAc)2 and 2 equiv of SiCl4
afforded the best combination of rate and monoenoxysi-
lane selectivity; the corresponding trichlorosilyl enolates
could be isolated in reproducibly good yield, Table 3. It
was also demonstrated that other chlorosilane derivatives
participated in this reaction, with the hydridodichlorosilyl
enolate 13 being formed in moderate yield using 4 mol
% Hg(OAc)2, Table 3, entry 3.
10g
a
b
Yield of distilled product. Z/E > 50/1.
amenable to this procedure, and it remains our method
of choice for the preparation of 10a .
As noted above, the stannane route is also quite useful
for the preparation of certain ketone-derived chlorosilyl
enolates, though the method is limited by the availability
of regiochemically pure stannyl ketone derivatives 11,9
often from the corresponding enol acetates, Scheme 3.
Both the trichlorosilyl enolates derived from acetone and
cyclohexanone2e can be prepared by this three-step
procedure in moderate yield from the starting ketone. In
most cases, purification of the stannyl ketone is not
required, thus simplifying the overall process. Treatment
of the enol acetate with Bu3SnOMe at roughly 100 °C,10
followed by removal of the methyl acetate and direct
treatment of the crude stannyl ketones with excess SiCl4
(again to preclude formation of poly(enoxy)silanes), led
to the pure trichlorosilyl enolates 10b-g in moderate to
good yield after distillation, Table 2. In the case of
propiophenone, excellent Z selectivity (>50/1) was ob-
served in the formation of the trichlorosilyl enolate.
Unlike their ester counterparts, these enolates are
thermally stable and can be distilled at temperatures up
to 140 °C under reduced pressure without complication.
In fact, we have yet to observe a C-(trichlorosilyl) ketone
in the course of these studies, and it is likely that the
O-silyl isomers are significantly more thermodynamically
stable.
The use of trichlorosilyl triflate in the synthesis of
ketone enolates has also been investigated, both in trans-
silylation reactions and direct enolsilylation. Though
C-(trialkylsilyl) ketones have not been utilized, when the
TMS enol ether 12h was treated with trichlorosilyl
triflate in CDCl3, rapid trans-silylation to form the
chlorosilyl enolate 10h occurred, Scheme 4. Unfortu-
nately, on a preparative scale, pure samples of the
enolate could not be obtained. Direct enolsilylation of
cyclohexanone proceeded as above with i-Pr2NEt and
trichlorosilyl triflate, and though good yields could
sometimes be obtained, the reaction as currently devel-
oped is too capricious for general preparative purposes.
Attempts at direct enolsilylation of methyl isobutyl
ketone with trichlorosilyl triflate and various amine bases
led only to complex mixtures.
This procedure has been used to create an extensive
collection of methyl ketone-derived enolates now using
only 1 mol % Hg(OAc)2, Table 4. Common protecting
groups (Table 4, entries 5 and 8-10) and other acid
(11) (a) House, H. O.; Auerbach, R. A.; Gall, M.; Peet, N. P. J . Org.
Chem. 1973, 38, 514. (b) Yamamoto, Y.; Maruyama, K. J . Am. Chem.
Soc. 1982, 104, 2323. (c) Bluthe, N.; Malacria, M.; Gore, J . Tetrahedron
1984, 40, 3277. (d) Drouin, J .; Boaventura, M.-A.; Conia, J .-M. J . Am.
Chem. Soc. 1985, 107, 1726.
(12) (a) Nakamura, E.; Kuwajima, I. Chem. Lett. 1983, 59. (b)
Nakamura, E.; Kuwajima, I. Tetrahedron Lett. 1983, 24, 3347. (c)
Annunziata, R.; Benaglia, M.; Cinquini, M.; Cozzi, F.; Raimondi, L.
Tetrahedron 1994, 50, 5821. (d) Kuwajima, I.; Nakamura, E. Acc.
Chem. Res. 1985, 18, 181.
(9) For leading references on alkyltin enolates see: (a) Yasuda, M.;
Katoh, Y.; Shibata, I.; Baba, A.; Matsuda, H.; Sonoda, N. J . Org. Chem.
1994, 59, 4386. (b) Shibata, I.; Baba, A. Org. Prep. Proced. Int. 1994,
26, 85. Recently, an interesting asymmetric aldol addition utlizing such
stannanes directly has appeared appeared; see: (c) Yanagisawa, A.;
Matsumoto, Y.; Nakashima, H.; Asakawa, K.; Yamamoto, H. J . Am.
Chem. Soc. 1997, 119, 9319.
(10) Pereyre, M.; Bellegarde, B.; Mendelsohn, J .; Valade, J . J .
Organomet. Chem. 1968, 11, 97.

9520 J . Org. Chem., Vol. 63, No. 25, 1998
Denmark et al.
Ta ble 3. Syn th esis of Cyclic Keton e Ch lor osilyl En ola tes
by Tr a n s-Silyla tion
necessary and tedious due the presence of Bu3SnCl and,
in some instances, excess chlorosilane. Although the
preparation of ketone enolates by this method is general
and reasonably efficient when the desired enol acetate
is conveniently prepared, the limited availability of
regiochemically pure enol acetates does present a barrier
to the general utility of this method.
Hg(OAc)2,
mol %
The use of trichlorosilyl triflate as a trichlorosilylating
reagent allows for the use of metathetical reactions using
substrates with weaker electrofuges, i.e., alkylsilanes.
These reactions seem to be fairly general over a range of
ester and ketone substrates, though the preparative
utility is low due to the complicated mixtures often
observed and the ready decomposition of the product in
the reaction mixture (even in cases where the isolated
trichlorosilyl enolates are known to be stable). These
problems may stem from undetected impurities in trichlo-
rosilyl triflate or be due to impurities formed during the
course of the reactions. The use of trichlorosilyl triflate
(or perhaps related reagents) in direct enolsilylation is
potentially the most convenient and powerful method for
the synthesis of trichlorosilyl enolates, though it is
currently hampered by limited substrate generality and
the capricious nature of the reaction even with substrates
amenable to the process.
The trans-silylation reaction from TMS enol ethers
catalyzed by Hg(OAc)2 is currently the most general and
efficient method for the preparation of chlorosilyl enolates
of ketones. Indeed, for methyl ketones the process is
extremely facile, with good results being obtained even
at 400/1 substrate/catalyst ratio. Cyclic ketones are much
less reactive in this process (presumably due to steric
hindrance of one or both of the steps in the process), and
hence, more catalyst (4-5 mol %) is required, in addition
to longer reaction times (18-24 h versus 1-2 h for
methyl ketones). The largest problem in the reaction is
the formation of 10-15% of the bis(enoxy)dichlorosilane,
lowering the overall yield of the process, though the crude
reaction mixture seems to contain only mono- and bis-
(enoxy) species and TMSCl. A cursory investigation of
other metal salts demonstrated that, of those surveyed,
Hg(OAc)2 was the most selective for the mono(enoxy)
species. The dramatic drop in rate when either overall
concentration of the reaction or a large (3-5 equivalents)
excess of SiCl4 is used is intriguing. Presumably, this is
due to a catalyst deactivation pathway, though the
process involved is not clear at the present time. We feel
that, from the precedent of both House11 and Baukov,2
the mercury salt electrophilically adds to the starting enol
ether, forming a transient R-mercurio ketone, with loss
of the trimethylsilyl group, Scheme 6. Coordination of
SiCl4 to the carbonyl and assisted loss of the mercury
electrofuge would then form the trichlorosilyl enolate and
reform an active mercury salt for the next catalytic cycle.
entry
n
enol ether
R
enolate yield,a
%
1
2
3
4
5
6
6
7
12e
12f
12f
12g
5
5
4
5
Cl
Cl
H
10e
10f
13
73
68
59
78
Cl
10g
a
Yield of distilled product.
Ta ble 4. Syn th esis of Meth yl Keton e Tr ich lor osilyl
En ola tes by Tr a n s-Silyla tion
entry
enol ether
R1
enolate
yield,b %
1
2
3
4
5
6
7
8
9
12h
12i
12j
12b
12k
12l
12c
14a
14b
14c
i-Pr
n-Bu
i-Bu
t-Bu
TBSOCH2
CH2tCH
Ph
OTBS
OPiv
10h
10i
10j
10b
10k
10l
10c
15a
15b
15c
83
83
74
81
65
61
69
71
78
60
10
OBn
a
b
1 mol % Hg(OAc)2/SiCl4/CH2Cl2/rt. Yield of distilled product.
Sch em e 5
sensitive substrates (Table 4, entry 6) are compatible
with this reagent combination so long as care is taken to
perform the reaction under anhydrous conditions. In
addition, unsymmetrical methyl ketone enolates are now
easily available from the TMS enol ethers, whereas with
the tin-based method such substrates would be difficult
to obtain in regiochemically pure form. In further studies
with TMS enol ether 14a it was found that as little as
0.25 mol % Hg(OAc)2 could be used effectively in the
transformation with only slight reduction in rate (roughly
30-60 min reaction time at room temperature). The
phenyldichlorosilyl enolate 16 was also available in
modest yield via the mercury-catalyzed trans-silylation
reaction, Scheme 5. The efficacy of this catalytic trans-
silylation has allowed the use of trichlorosilyl enolates
as aldolization reagents without the need for purification.
Thus, treatment of TMS enol ethers with SiCl4 and
catalytic Hg(OAc)2 followed by concentration provides
crude trichlorosilyl enolate of sufficient purity to be used
in subsequent asymmetric aldol additions without sig-
nificantly changed yield or selectivity.1d,1f
Sch em e 6
Discu ssion
The synthesis of chlorosilyl enolates of both esters and
ketones by the silicon-tin metathesis reaction is cer-
tainly general, though purification of the products is both
We recognize that this is a primitive mechanistic
picture as we are not certain of the exact nature of the

Preparation of Chlorosilyl Enolates
J . Org. Chem., Vol. 63, No. 25, 1998 9521
an addition funnel to cold (0 °C) SiCl4 (46.0 mL, 403 mmol,
3.0 equiv) over 3 h with vigorous stirring. After complete
addition, the mixture was warmed to room temperature and
stirred for an additional 3 h. Excess SiCl4 was removed by
simple distillation, and the residue was fractionated twice
through a 5-cm Vigreux column under reduced pressure to
afford 24.2 g (78%) of the trichlorosilyl enolate 10f as a
chlorosilylating species nor of the nucleophile that assists
the loss of the mercury electrofuge. A detailed mecha-
nistic study is in progress.
In conclusion, we have accomplished the syntheses of
26 chlorosilyl enolates (most of which have been applied
to aldol addition reactions) by a number of independent
methods. Although capricious, trans-silylation and direct
enolsilylation with trichlorosilyl triflate are both promis-
ing processes for the general preparation of chlorosilyl
enolates, while the mercury-catalyzed trans-silylation
seems to be a much preferred method over the traditional
stannane-silicon metathesis route. Efforts toward the
selective synthesis of both E- and Z-configured enolates
of simple ethyl ketones and more direct methods for the
synthesis of chlorosilyl enolates continue.
1
colorless liquid: bp 76-78 °C (11 mmHg); H NMR (CDCl3,
400 MHz) δ 5.31-5.28 (m, 1 H), 2.17-2.13 (m, 2 H), 2.09-
2.04 (m, 2 H), 1.74-1.68 (m, 2 H), 1.58-1.52 (m, 2 H); 13C NMR
(CDCl3, 100 MHz) δ 148.07, 109.13, 28.54, 23.56, 22.74, 21.65;
IR (CHCl3) 1459 (m) cm-1; MS (EI) m/z 234 (28), 233 (26), 232
(73), 231 (56), 230 (73), 229 (47), 202 (100). Anal. Calcd for
C6H9Cl3OSi (231.58): C, 31.12; H, 3.92; Cl, 45.93. Found: C,
31.49; H, 4.08; Cl, 45.54.
Trichloro[1-phenyl-[(1-propenyl)oxy]silane (10d). 1-Phen-
yl-[(1-propenyl)oxy]acetate13 (18.95 g, 107.5 mmol) and tribu-
tyltin methoxide (31.0 mL, 107.5 mmol, 1.0 equiv) were heated
to 100 °C (bath temperature) for 4 h. The methyl acetate
formed was continuously removed via a 10-cm Vigreux column.
The mixture was cooled to room temperature, and the flask
was carefully evacuated to 0.05 mmHg and heated to 100 °C
(bath temperature) for 30 min to provide tributyl[(1-phenyl-
1-propenenyl)oxy]stannane, which was used without further
purification. The tributylstannyl compound was then added
to cold (0 °C) SiCl4 (37.0 mL, 323 mmol, 3.0 equiv) through an
addition funnel over 2.5 h. The mixture was warmed to room
temperature and stirred for an additional 3 h. Excess SiCl4
was removed by distillation, and the residue was fractionated
twice through a 5-cm Vigreux column to give 23.8 g (83%) of
the trichlorosilyl enolate 10d as a pale yellow liquid: 1H NMR
(CDCl3, 400 MHz) δ 7.53-7.51 (m, 2 H), 7.40-7.31 (m, 3 H),
5.63 (q, J ) 7.1, 1 H), 1.88 (d, J ) 7.1, 3 H); 13C NMR (CDCl3,
100 MHz) δ 147.66, 135.72, 128.38, 128.25, 125.03, 108.82,
11.94; IR (neat) 1496 (m) cm-1; MS (EI) m/z 270 (6), 269 (11),
268 (17), 267 (25), 266 (18), 265 (24). Anal. Calcd for C9H9Cl3OSi
(267.62): C, 40.39; H, 3.39; Cl, 39.74. Found: C, 40.19; H, 3.38;
Cl, 39.65.
Exp er im en ta l Section
Gen er a l Meth od s. See the Supporting Information.
Tr ich lor o[(1-m eth oxyeth en yl)oxy]sila n e (2b). Methyl
(tributylstannyl)acetate (1)4 (18.46 g, 50.8 mmol) was added
to SiCl4 (35 mL, 306 mmol, 6 equiv) at room temperature under
argon with vigorous stirring. The mixture was maintained at
room temperature until 1H NMR spectra of aliquots indicated
that the stannyl ester had been consumed (typically 6-24 h).
The excess SiCl4 was removed under reduced pressure, and
the residue was distilled at reduced pressure (two to three
distillations were usually required) to give 6.82 g (65%) of the
silyl ketene acetal 2b2a as a clear, colorless liquid: bp 25 °C
1
(5 mmHg); H NMR (CDCl3, 500 MHz) δ 3.65 (d, J ) 4.0, 1
H), 3.64 (s, 3 H), 3.41 (d, J ) 3.9, 1 H); 13C NMR (CDCl3, 126
MHz) δ 158.33, 64.70, 56.13; IR (neat) 1672 (s) cm-1; MS (CI)
m/z 209 (9), 207 (8), 75 (100); HRMS calcd for C3H635Cl37Cl2O2Si
210.9144, found 210.9145. Anal. Calcd for C3H5Cl3O2Si
(207.52): C, 17.36; H, 2.43; Cl, 51.25. Found: C, 17.53; H, 2.53;
Cl, 51.08.
4-Meth yl-2,6-bis(1,1-d im eth yleth yl)p h en yl 2-(Tr im eth -
ylsilyl)p r op a n oa te (4). n-Butyllithium (6.2 mL of a 1.72 M
solution in hexanes, 10.7 mmol, 1.01 equiv) was added quickly
to a cold (0 °C) solution of i-Pr2NH (1.50 mL, 10.7 mmol, 1.2
equiv) in THF (40 mL). The resulting solution was stirred at
0 °C for 10 min and then cooled to -75 °C (internal). A solution
of ester7 (2.8 mL, 10.5 mmol) in THF (10 mL) was then added
dropwise over 30 min. After the final addition, the reaction
mixture was stirred at -75 to -77 °C for 30 min, and then
TMSCl (1.90 mL, 15.0 mmol, 1.5 equiv) was added quickly,
during which time the temperature rose to -71 °C. The
mixture was allowed to warm to room temperature slowly and
stirred for 12 h. Volatile components were removed under
reduced pressure (0.3 mmHg), pentane (30 mL) was added,
and the resulting slurry was Schlenk filtered. The filtrate was
concentrated under reduced pressure (0.3 mmHg) to give a
residue that was crystallized from hexane to provide 2.45 g
(67%) of the C-TMS compound 4 as white crystals: 1H NMR
(CDCl3, 500 MHz) δ 7.11 (s, 1 H), 7.11 (s, 1 H), 2.30 (s, 3 H),
2.26 (q, J ) 7.3, 1 H), 1.45 (d, J ) 7.3, 3 H), 1.34 (s, 9 H), 1.33
(s, 9 H), 0.19 (s, 9 H); 13C NMR (CDCl3, 126 MHz) δ 175.47,
146.64, 142.14, 141.83, 134.10, 127.07, 126.78, 35.33, 35.21,
31.66, 31.49, 31.27, 21.44, 11.34, -1.68.
Tr ich lor o[[[4-m et h yl-2,6-bis(1,1-d im et h ylet h yl)p h en -
oxy]p r op en yl]oxy]sila n e (5). Trichlorosilyl triflate6 (95 µL,
0.55 mmol, 1.2 equiv) was added quickly to a cold (0 °C)
solution of ester 4 in CDCl3 (0.5 mL). The reaction mixture
was allowed to stand at room temperature for 30 h, at which
time no starting silane was observed in the 1H NMR spectrum.
Removal of the volatile components under reduced pressure
(0.1 mmHg) provided the trichlorosilyl enolate 5 in essentially
quantitative yield: 1H NMR (CDCl3, 500 MHz) δ 7.10 (s, 2
H), 4.07 (q, J ) 6.8, 1 H), 2.36 (s, 3 H), 1.46 (s, 18 H), 1.1 (d,
J ) 6.8, 3 H).
Da ta for d ich lor o[(1-m eth oxyeth en yl)oxy]sila n e (2a ):
bp 0 °C (5 mmHg); 1H NMR (CDCl3, 500 MHz) δ 5.73 (s, 1 H),
3.63 (s, 3 H), 3.58 (d, J ) 3.7, 1 H), 3.34 (d, J ) 3.9, 1 H); 13
C
NMR (CDCl3, 126 MHz) δ 158.88, 63.55, 55.99; IR (neat) 1677
(s) cm-1; MS (CI) m/z 177 (12), 175 (52), 173 (75), 171 (15), 75
(100); HRMS calcd for C3H535Cl2O2Si 170.9436, found 170.9429.
Anal. Calcd for C3H6Cl2O2Si (173.07): Cl, 40.97. Found: Cl,
41.18.
Da ta for d ich lor o[(1-m eth oxyeth en yl)oxy]m eth ylsi-
la n e (2c): bp 25 °C (0.5 mmHg); 1H NMR (CDCl3, 500 MHz)
δ 3.61 (s, 3 H), 3.57 (d, J ) 3.6, 1 H), 3.34 (d, J ) 3.6, 1 H),
0.89 (s, 3H); 13C NMR (CDCl3, 126 MHz) δ 159.02, 63.64, 55.79,
4.95; IR (neat) 1764 (s), 1747 (s) cm-1; MS (CI) m/z 187 (M +
1, 27) 186 (11), 151 (100); HRMS calcd for C4H935Cl2O2Si
186.9749, found 186.9747.
Da ta for d ich lor o[(1-m eth oxyeth en yl)oxy]p h en ylsi-
la n e (2d ): bp 65 °C (0.02 mmHg); 1H NMR (CDCl3, 500 MHz)
δ 7.79 (br d, J ) 7.2, 2 H), 7.55 (br t, J ) 7.5, 1 H), 7.47 (t, J
) 7.4, 2 H), 3.64 (d, J ) 3.6, 1 H), 3.60 (s, 3 H), 3.37 (d, J )
3.6, 1 H); 13C NMR (CDCl3, 126 MHz) δ 159.05, 133.65, 132.67,
130.18, 128.30, 64.05, 55.81; IR (neat) 1733 (m), 1666 (s) cm-1
;
MS (FI) m/z 252 (18), 248 (100).
Da ta for ch lor o[(1-m eth oxyvin yl)oxy]d im eth ylsila n e
(2e): bp 25 °C (0.5 mmHg); 1H NMR (CDCl3, 500 MHz) δ 3.58
(s, 3 H), 3.45 (d, J ) 3.2, 1 H), 3.24 (d, J ) 3.2, 1 H), 0.58 (s,
6 H); 13C NMR (CDCl3, 126 MHz) δ 160.32, 62.09, 55.44, 2.43,
2.40.
Da ta for ch lor o[(1-m eth oxyeth en yl)oxy]sila cyclobu -
ta n e (2f): bp 25 °C (0.02 mmHg); 1H NMR (CDCl3, 500 MHz)
δ 3.46 (d, J ) 3.4, 1 H), 3.60 (s, 3 H), 3.27 (d, J ) 3.4, 1 H),
2.01-1.79 (m, 4 H), 1.78-1.68 (m, 2 H); 13C NMR (CDCl3, 126
MHz) δ 159.74, 62.08, 55.67, 25.03, 12.55; IR (neat) 1728 (s),
1666 (s) cm-1; MS (CI) m/z 179 (M + 1, 6), 75 (100); HRMS
calcd for C6H1235ClO2Si 179.0295, found 179.0296.
Tr ich lor o[(1-cycloh exen yl)oxy]sila n e (10f). Tributyl[(1-
(13) Foss, V. L.; Sorokin, N. M.; Avrutov, I. M.; Lutsenko, I. F. J .
Organomet. Chem. 1974, 78, 115.
cyclohexenyl)oxy]stannane9c (52.0 g, 134 mmol) was added via

9522 J . Org. Chem., Vol. 63, No. 25, 1998
Denmark et al.
Tr ich lor o[(3,4-d ih yd r o-2H-p yr a n -6-yl)oxy]sila n e (6).
Trichlorosilyl triflate (1.0 mL, 5.76 mmol, 1.3 equiv) was added
dropwise to δ-valerolactone (0.4 mL, 4.3 mmol) in dry pentane
(50 mL) at 0 °C. After 10 min at this temperature, i-Pr2NEt
(0.8 mL, 5.76 mmol, 1.3 equiv) was added dropwise over 30
min. A white precipitate formed during the addition. The
mixture was stirred at 0 °C for 45 min and then was warmed
to room temperature, Schlenk filtered under argon, and
concentrated under reduced pressure (∼40 mmHg). The resi-
due was purified by distillation (bulb-to-bulb) to give 0.506 g
(48%) the silyl ketene acetal 6 as a colorless liquid: bp 25 °C
Da t a for d ich lor o[[1-(2-m et h ylp r op yl)et h en yl]oxy]-
p h en ylsila n e (16): bp 77 °C (0.15 mmHg); 1H NMR (CDCl3,
500 MHz) δ 7.78 (dd, J ) 8.1, 1.3, 2 H), 7.56 (tt, J ) 7.5, 2.0,
1 H), 7.48 (t, J ) 7.5, 2 H), 4.57 (d, J ) 1.6, 1 H), 4.33 (d, J )
1.6, 1 H), 2.04 (d, J ) 7.1, 2 H), 1.91 (nonet, J ) 7.3, 1 H),
0.93 (d, J ) 6.6, 6 H).
Da ta for tr ich lor o[[1-(m eth yleth yl)eth en yl]oxy]sila n e
1
(10h ): bp 78-80 °C (75 mmHg); H NMR (CDCl3, 500 MHz)
δ 4.51 (d, J ) 2.4, 1 H), 4.15 (dd, J ) 2.4, 0.8, 1 H), 2.36 (sept
d, J sept ) 6.8, J d ) 0.2, 1 H), 1.09 (d, J ) 6.8, 6 H); 13C NMR
(CDCl3, 126 MHz) δ 161.63, 93.18, 33.60, 20.03; IR (neat) 1647
(m) cm-1; MS (CI) m/z 221 (1), 219 (1), 60 (100). Anal. Calcd
for C5H9Cl3OSi (219.57): C, 27.35; H, 4.13; Cl, 48.44. Found:
C, 27.15; H, 4.41; Cl, 48.50.
1
ABT (0.02 mmHg); H NMR (CDCl3, 500 MHz) δ 4.21 (t, J )
3.7, 1 H), 4.14 (br t, J ) 5.1), 2.09 (td, J ) 6.4, 3.7, 2 H), 1.84-
1.79 (m, 2 H).
Da ta for tr ich lor o[[1-(1,1-d im eth yleth yl)eth en yl]oxy]-
sila n e (10b): bp 90-91 °C (80 mmHg); 1H NMR (CDCl3, 500
MHz) δ 4.47 (d, J ) 2.8, 1 H), 4.46 (d, J ) 2.7, 1 H), 1.11 (s, 9
H); 13C NMR (CDCl3, 126 MHz) δ 164.23, 92.06, 36.23, 27.66;
IR (neat) 1643 (s) cm-1; MS (CI) m/z 237 (1), 235 (2), 233 (2),
101 (100). Anal. Calcd for C6H11Cl3OSi (233.60): C, 30.85; H,
4.75; Cl, 45.53. Found: C, 30.69; H, 4.76; Cl, 45.61.
Da t a for t r ich lor o[(3,4-d ih yd r o-2H -t h ia p yr a n -6-yl)-
oxy]sila n e (7): bp 80 °C ABT (0.3 mmHg); 1H NMR (CDCl3,
400 MHz) δ 5.41 (t, J ) 3.9, 1 H), 2.99-2.96 (m, 2 H), 2.28-
2.21 (m, 2 H), 1.98-1.90 (m, 2 H).
Da ta for tr ich lor o[[(1-(d im eth ylp h en ylsilyl)p r op en yl]-
oxy]sila n e (9): bp 120 °C ABT (0.03 mmHg); 1H NMR (CDCl3,
500 MHz) δ 7.57-7.54 (m, 2 H), 7.40-7.35 (m, 3 H), 6.07 (q,
J ) 7.4, E), 4.37 (q, J ) 6.8, Z), 1.69 (d, J ) 6.9, Z), 1.50 (d, J
) 7.3, E), 0.48 (s, E) 0.45 (s, Z).
Tr ich lor o[(1-m eth yleth en yl)oxy]sila n e (10a ). Chloro-
acetone (6.37 mL, 80.0 mmol) was added dropwise over 15 min
to a 0 °C solution of n-Bu3N (19.06 mL, 80.0 mmol, 1.0 equiv)
and trichlorosilane (8.07 mL, 80.0 mmol, 1.0 equiv) in pentane
(40 mL). During the addition, an oily phase appeared that
eventually solidified. After the addition, the heterogeneous
mixture was warmed to room temperature and stirred for 18
h. The volatile materials were then vacuum transferred at 0.2
mmHg to a new flask. The pentane was removed at reduced
pressure (200 mmHg), and the resulting oil was distilled twice
through a 7.5 cm Vigreux column to give 9.65 g (63%) of the
trichlorosilyl enolate 10a as a clear, colorless liquid: bp 63-
64 °C (110 mmHg); 1H NMR (CDCl3, 500 MHz) δ 4.55 (br d, J
) 1.1, 1 H), 4.42 (br s, 1 H), 1.92 (s, 3 H); 13C NMR (CDCl3,
126 MHz) 152.62, 96.94, 21.44; IR (neat) 1659 (s) cm-1; MS
(CI) m/z 197 (15), 195 (14), 193 (6), 191 (2), 59 (100); HRMS
calcd for C3H6Cl3OSi 190.9254, found 190.9250.
Da ta for tr ich lor o[(1-p h en yleth en yl)oxy]sila n e (10c):
1
bp 85-87 °C (3 mmHg); H NMR (CDCl3, 500 MHz) δ 7.59-
7.56 (m, 2 H), 7.40-7.35 (m, 3 H), 5.23 (d, J ) 2.9, 1 H), 4.92
(d, J ) 2.9, 1 H); 13C NMR (CDCl3, 126 MHz) δ 152.94, 134.31,
129.24, 128.46, 125.16, 95.93; IR (neat) 1631 (s) cm-1; MS (CI)
m/z 255 (1), 253 (2), 105 (100). Anal. Calcd for C8H7Cl3OSi
(253.59): C, 37.89; H, 2.78; Cl, 41.94. Found: C, 37.96; H, 2.96;
Cl, 41.91.
Da ta for tr ich lor o[[1-[[[d im eth yl(1,1-d im eth yleth yl)-
silyl]oxy]m eth yl]eth en yl]oxy]sila n e (10k ): bp 74-75 °C
(3 mmHg); 1H NMR (CDCl3, 500 MHz) δ 4.76 (br s, 1 H), 4.71
(br s, 1 H), 4.06 (br t, J ) 1.1, 2 H), 0.92 (s, 9 H), 0.09 (s, 6 H);
13C NMR (CDCl3, 126 MHz) δ 154.54, 95.29, 62.82, 25.81,
18.33, -5.46; IR (neat) 1663 (s) cm-1; MS (CI) m/z 327 (4), 325
(12), 323 (23), 321 (18). Anal. Calcd for C9H19Cl3O2Si2
(321.78): C, 33.59; H, 5.95; Cl, 33.05. Found: C, 33.89; H, 6.27;
Cl, 33.16.
Da ta for tr ich lor o[(1-bu ta d ien yl)oxy]sila n e (10l): bp
63-64 °C (65 mmHg); 1H NMR (CDCl3, 500 MHz) δ 6.19 (dd,
J ) 17.0, 6.2, 1 H), 5.53 (d, J ) 17.0, 1 H), 5.24 (d, J ) 6.4, 1
H), 4.82 (m, 1 H), 4.68 (d, J ) 2.2, 1 H).
Tr ich lor o[(1-bu tyleth en yl)oxy]sila n e (10i). Silicon tet-
rachloride (9.18 mL, 80.0 mmol, 2.0 equiv) was added quickly
to a suspension of Hg(OAc)2 (127.0 mg, 0.40 mmol, 0.01 equiv)
in CH2Cl2 (40 mL). During the addition, the mercury salt
dissolved. Silyl enol ether 12i14 (6.89 g, 40.0 mmol) was then
added to the solution dropwise over 10 min, and the solution
was stirred at room temperature for an additional 50 min.
During this time, the reaction mixture became somewhat
Da ta for (S)-tr ich lor o[[1-[[[d im eth yl(1,1-d im eth yleth -
yl)silyl]oxy]eth yl]eth en yl]oxy]sila n e (15a ): bp 140 °C
(ABT, 12 mmHg); 1H NMR (CDCl3, 500 MHz) δ 4.75 (dd, J )
2.2, 0.9, 1 H), 4.62 (d, J ) 2.2, 1 H), 4.16 (q, J ) 6.4, 1 H), 1.29
(d, J ) 6.2, 3 H), 0.91 (s, 9 H), 0.08 (s, 3 H), 0.08 (s, 3 H); 13C
NMR (CDCl3, 126 MHz) δ 158.58, 94.05, 68.54, 25.76, 22.04,
18.17, -4.94, -5.10; MS (CI) m/z 337 (15), 335 (16); HRMS
calcd for C10H22Cl3O2Si2 335.0224, found 335.0225.
Da ta for (S)-[1-m eth yl-2-[(tr ich lor osilyl)oxy]-2-p r op en -
yl]-2,2-d im eth ylp r op a n oa te (15b): bp 140 °C (ABT, 8
1
cloudy once again. Removal of an aliquot and H NMR analysis
indicated that the reaction was complete. The mixture was
concentrated at reduced pressure (100 mmHg), and the result-
ing oil was distilled twice through a 7.5 cm Vigreux column to
give 7.76 g (83%) of the trichlorosilyl enolate 10i as a clear,
1
mmHg); H NMR (CDCl3, 500 MHz) δ 5.28 (q, J ) 6.6, 1 H),
4.72 (app q, J ) 2.8, 2 H), 1.37 (d, J ) 6.6, 3 H), 1.21 (s, 9 H);
13C NMR (CDCl3, 126 MHz) δ 177.36, 154.03, 96.76, 69.31,
38.71, 27.04, 17.63.
1
colorless oil: bp 68-70 °C (15 mmHg); H NMR (CDCl3, 500
MHz) δ 4.56 (br d, J ) 1.9, 1 H), 4.41 (br s, 1 H), 2.16 (t, J )
7.1, 2 H), 1.49 (m, 2 H), 1.35 (sext, J ) 7.5, 2 H), 0.92 (t, J )
7.3, 3 H); 13C NMR (CDCl3, 126 MHz) δ 156.43, 95.62, 34.77,
28.41, 21.94, 13.78; IR (neat) 1655 (s) cm-1; MS (CI) m/z 239
(4), 237 (4), 235 (10), 233 (11), 180 (100). Anal. Calcd for
C6H11Cl3OSi (233.60): C, 30.85; H, 4.75; Cl, 45.53. Found: C,
30.93; H, 5.04; Cl, 45.54.
Da t a for (S)-t r ich lor o[(1-(p h en ylm et h oxy)et h en yl)-
oxy]sila n e (15c): bp 130 °C (ABT, 0.3 mmHg); 1H NMR
(CDCl3, 500 MHz) δ 7.37-7.29 (m, 5 H), 4.79 (dd, J ) 2.4, 0.7,
1 H), 4.74 (d, J ) 2.4, 1 H), 4.66 (d, J ) 11.9, 1 H), 4.42 (d, J
) 12.0, 1 H), 3.88 (q, J ) 6.4, 1 H), 1.37 (d, J ) 6.4, 3 H); 13C
NMR (CDCl3, 126 MHz) δ 155.18, 138.07, 128.42, 127.70,
127.67, 96.80, 74.92, 70.58, 19.13.
Da ta for tr ich lor o[(cyclop en ten yl)oxy]sila n e (10e): bp
45-46 °C (7 mmHg); 1H NMR (CDCl3, 500 MHz) δ 5.10 (pent,
J ) 2.0, 1 H), 2.44-2.40 (m, 2 H), 2.36-2.31 (m, 2 H), 1.98-
1.90 (m, 2 H); 13C NMR (CDCl3, 126 MHz) δ 150.75, 108.38,
32.14, 28.30, 20.99; IR (neat) 1657 (s) cm-1; MS (EI) m/z 222
(3), 220 (5), 218 (11), 216 (18), 55 (100). Anal. Calcd for
C5H7Cl3OSi (217.55): C, 27.60; H, 3.24; Cl, 48.89. Found: C,
27.61; H, 3.35; Cl, 48.60.
Da ta for tr ich lor o[[1-(2-m eth ylp r op yl)eth en yl]oxy]si-
la n e (10j): bp 98-99 °C (90 mmHg); 1H NMR (CDCl3, 500
MHz) δ 4.58 (br d, J ) 2.1, 1 H), 4.39 (br d, J ) 1.1, 1 H), 2.01
(d, J ) 7.1, 2 H), 1.88 (sept, J ) 6.8, 1 H), 0.93 (d, J ) 6.6, 6
H); 13C NMR (CDCl3, 126 MHz) δ 155.36, 96.77, 44.49, 25.34,
22.09; IR (neat) 1655 (s) cm-1; MS (CI) m/z 239 (2), 237 (3),
235 (6), 233 (12), 83 (100). Anal. Calcd for C6H11Cl3OSi
(233.60): C, 30.85; H, 4.75; Cl, 45.53. Found: C, 30.80; H, 5.00;
Cl, 45.27.
Da ta for d ich lor o[(cycloh exen yl)oxy]sila n e (13): bp
84-85 °C (30 mmHg); 1H NMR (CDCl3, 400 MHz) δ 5.66 (s, 1
H), 5.22-2.19 (m, 1 H), 2.14-2.08 (m, 2 H), 2.07-2.02 (m, 2
H), 1.74-1.66 (m, 2 H), 1.57-1.50 (m, 2 H).
(14) (a) Haslouin, J .; Rouessac, F. Bull. Chem. Soc. Fr. 1976, 1122.
(b) Camici, L.; Dembech, P.; Ricci, A.; Seconi, G.; Taddei, M. Tetrahe-
dron 1988, 44, 4197.

Preparation of Chlorosilyl Enolates
J . Org. Chem., Vol. 63, No. 25, 1998 9523
Da ta for tr ich lor o[(cycloh ep ten yl)oxy]sila n e (10g): bp
84-85 °C (10 mmHg); 1H NMR (CDCl3, 500 MHz) δ 5.44 (t, J
) 6.5, 1 H), 2.38-2.35 (m, 2 H), 2.05 (br q, J ) 4.9, 2 H), 1.73-
1.50 (m, 6 H); 13C NMR (CDCl3, 126 MHz) δ 152.80, 113.78,
34.16, 30.68, 27.06, 24.93, 24.00; IR (neat) 1673 (s) cm-1; MS
(EI) m/z 247 (2), 245 (2), 55 (100). Anal. Calcd for C7H11Cl3OSi
(245.61): C, 34.23; H, 4.51; Cl, 43.30. Found: C, 34.05; H, 4.67;
Cl, 43.48.
of Illinois and the Eastman Chemical Co. for Graduate
Fellowships.
Su p p or tin g In for m a tion Ava ila ble: Full experimental
procedures and characterization data for all compounds de-
scribed (35 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
Ack n ow led gm en t. We are grateful to the National
Science Foundation (CHE 9500397 and 9803124) for
support of this research. R.A.S. thanks the University
J O981740H