Stereoselective one-pot synthesis of vinylsilanes from aromatic aldehydes

Article abstract of DOI:10.1016/S0040-4039(00)02271-1

Vinylsilanes serve as convenient vinyl anion equivalents, but procedures for their stereoselective synthesis from aldehydes are scarce. A variety of aromatic aldehydes are converted to the corresponding vinylsilanes in a one-pot procedure involving the addition of (trimethylsilylmethyl)lithium to the aldehyde followed by treatment with Cp₂TiCH₂·AlMe₂Cl ('Tebbe's reagent'). Halide and alkoxide substituents are tolerated, and (E)-vinylsilanes are formed exclusively in good yield.

Full text of DOI:10.1016/S0040-4039(00)02271-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 1411–1413
Stereoselective one-pot synthesis of vinylsilanes from aromatic
aldehydes
Man Lung Kwan, Chiu W. Yeung, Kerry L. Breno and Kenneth M. Doxsee*
Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
Received 7 November 2000; revised 8 December 2000; accepted 11 December 2000
Abstract—Vinylsilanes serve as convenient vinyl anion equivalents, but procedures for their stereoselective synthesis from
aldehydes are scarce. A variety of aromatic aldehydes are converted to the corresponding vinylsilanes in a one-pot procedure
involving the addition of (trimethylsilylmethyl)lithium to the aldehyde followed by treatment with Cp2TiCH2·AlMe2Cl (‘Tebbe’s
reagent’). Halide and alkoxide substituents are tolerated, and (E)-vinylsilanes are formed exclusively in good yield. © 2001
Elsevier Science Ltd. All rights reserved.
The development of stereospecific alkene synthesis
methodology has been driven by the central role played
by the alkene functionality in countless natural and
unnatural products and synthetic intermediates. Vinyl-
silanes play important synthetic roles as vinyl anion
equivalents for stereospecific electrophilic reactions.1
However, few effective synthetic methods for the prepa-
ration of these versatile intermediates have been
reported. Although routes from alkynes have been
developed,2 the obvious Wittig approach from ketones
and/or aldehydes, using
a
substituted ylide,
Ph3PꢀCHSiMe3, is ineffective.3 Battiste and Kwan have
recently developed4 a protocol for the conversion of
non-enolizable ketones to vinylsilanes based on the
Peterson olefination reaction.5 Treatment of the lithium
alkoxide resulting from addition of (trimethylsilyl-
Scheme 1.
Table 1. Conversion of benzaldehyde to b-trimethylsilylstyrene
Reagents
Conditions
Yield
E:Z ratio
Reference
Cp2Ti(CH2SiMe3)2
CpTi(CH2SiMe3)3
(Me2SiOMe)2CH2/t-BuLi
Me3SiCHBr2/CrCl2
(Me3Si)2CHLi
(EtOCH2)2, 110°C, 26 h
(EtOCH2)2, 110°C, 26 h
100°C, 2 h
THF, 25°C, 24 h
THF, −78°C“25°C
Et2O, −78°C“25°C
20
40
85
82
70
90
B1.5:1
B1.5:1
3:1
1:0
1.4:1
\99:1
6
6
7
8
9
(2-PyMe2Si)2CHLi
10
Scheme 2.
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02271-1

1412
M. L. Kwan et al. / Tetrahedron Letters 42 (2001) 1411–1413
methyl)lithium to a ketone with diethylaluminum chlo-
ride in wet THF affords the corresponding vinylsilane
in fair to good yield (Scheme 1).
the trimethylsilyl group).4 In contrast, traces of water in
the titanium-mediated reaction lead to desilylation,
affording simple styrene derivatives. Drying of aldehyde
substrates (solids—Abderhalden pistol at 10–15°C
below the melting point of the aldehyde over P2O5;
liquids—washing with 10% sodium bicarbonate, then
distillation from CaH2, freeze–pump–thaw degassing,
This modified Peterson olefination approach fails with
aromatic aldehydes, forming complex mixtures of desi-
lylated, alkylated, and reduced materials together with
the desired vinylsilanes. Other methods for the conver-
sion of aldehydes to vinylsilanes generally suffer from
low yields, poor stereoselectivity, and/or expensive or
hazardous reagents, as summarized in Table 1.
,
and storage over activated 3 A molecular sieves) effec-
tively eliminates the desilylation reaction.
The reaction appears to form the vinylsilane exclusively
as the (E)-isomer, and yields range from 44 to 86%. An
electronic effect seems apparent, with the electron-rich
substrate, p-methoxybenzaldehyde, (Table 2, entry 1)
reacting appreciably faster than the p-bromo derivative.
The implications of this with regards to the mechanism
of the reaction are under continuing investigation. Sev-
eral aldehydes afford the (E)-vinylsilane cleanly (entries
1, 3, and 5). In other cases, however, formation of the
corresponding alkylsilane (b-trimethylsilylethylarene) is
also observed (entries 2, 4, and 6). Although separable
(e.g. capillary gas chromatography on a fused silica
column), we are continuing to explore the factors
responsible for formation of the reduction products in
order to minimize their formation.
Recognizing the ability of Cp2TiCH2·AlMe2Cl
(‘Tebbe’s reagent’) to cleave a variety of carbonꢁoxygen
bonds,11 we explored its reactions with b-silylalkoxides,
generated by the addition of (trimethylsilyl-
methyl)lithium to aromatic aldehydes. Upon addition
of the b-silylalkoxide to Tebbe’s reagent at room tem-
perature, a color change from brownish-red to purple-
1
red is observed. H NMR spectroscopy at this point
suggests that an alkoxide analog of Tebbe’s reagent has
formed. No additional significant chemistry occurs at
room temperature, but heating the reaction mixture to
ca. 150°C in a sealed tube leads to the production of
the corresponding (E)-vinylsilane (Scheme 2, Table 2).12
In the alumoxane-mediated synthesis of vinylsilanes
from non-enolizable ketones, the presence of water
appears to enhance the chemoselectivity of the reaction
(affording the desired abstraction of a proton instead of
Interestingly,
whereas
10-methyl-9-anthraldehyde
cleanly affords the anticipated (E)-vinylsilane in good
yield (entry 5), 9-anthraldehyde itself undergoes an
apparent dimerization reaction (as revealed by mass
Table 2. Vinylsilanes from aromatic aldehydes
Entry
Substrate ArCHO, Ar=
Reaction time (h)
Isolated yield (%)
Lit. Ref.
1a
2a
11.5
17
86
58
\99
4.7
B1
13
14
1
3b
4c
48
36
44
83
\99
B1
14
15
7.4
1
5b
48
74
82
\99
B1
–
6d
36.5
1.4
1
15
a Toluene, 110°C.
b Benzene, sealed tube, 150°C.
c Tetrahydrofuran, sealed tube, 150°C.
d Toluene, sealed tube, 150°C.

M. L. Kwan et al. / Tetrahedron Letters 42 (2001) 1411–1413
1413
spectral and partial X-ray crystallographic analysis).
The detailed structure of this product, whose formation
may also prove suggestive with regards to the mecha-
nism of the vinylsilane forming reaction, has proven
elusive due to crystallographic problems, but is under
continued investigation.
4. Kwan, M. L. Ph.D. Dissertation, University of Florida,
1999.
5. (a) Peterson, D. J. J. Org. Chem. 1968, 33, 780–784; (b)
Ager, D. A. In Organic Reactions; John Wiley & Sons:
New York, 1990; Vol. 38, Chapter 1; (c) Hudrlik, P. F.;
Agwaramgbo, E. L.; Hudrlik, A. M. J. Org. Chem. 1989,
54, 5613–5618; (d) Hudrlik, P. F.; Peterson, D. J. Am.
Chem. Soc. 1975, 97, 1464–1468; (e) Trindle, C.; Hwang,
J.-T.; Carey, F. A. J. Org. Chem. 1973, 38, 2664–2669.
6. Petasis, N. A.; Akritopoulou, I. Synlett 1992, 665–667.
7. Bates, T. F.; Thomas, R. D. J. Org. Chem. 1989, 54,
1784–1785.
This procedure provides convenient and reliable access
to a variety of vinylsilanes with excellent stereoselectiv-
ity. We are continuing to explore the versatility of this
reaction, as well as the factors responsible for the
formation of reduction products.
8. Takai, K.; Kataoka, Y.; Okazoe, T.; Utimoto, K. Tetra-
hedron Lett. 1987, 28, 1443–1446.
9. Gro¨bel, B.-T.; Seebach, D. Chem. Ber. 1977, 110, 852–
866.
Acknowledgements
10. Itami, K.; Nokami, T.; Yoshida, J.-i. Org. Lett. 2000, 2,
1299–1302.
11. Pine, S. H. In Organic Reactions; John Wiley & Sons:
New York, 1993; Vol. 43, pp. 1–91.
This work was supported by a grant from the National
Science Foundation.
12. General procedure: Under an inert atmosphere, 1.1 equiv.
of Me3SiCH2Li (1.3 M solution in benzene) was added to
a solution of 1.7 mmol of the aromatic aldehyde in 10
mL of dry benzene in a thick-walled tube with Teflon
closure. After stirring the solution at room temperature
for 2 h, a solution of 1.1 equiv. of Cp2TiCH2·AlMe2Cl in
40 mL of dry benzene was added, forming a deep-red
solution. The tube was closed, then heated in a 150°C oil
bath for 11–48 h (see Table 2). The resulting mixture was
transferred in air to a 500 mL beaker containing excess
sodium oxalate (ca. 15 g) and sodium bicarbonate (ca. 1
g). The mixture was stirred overnight, affording a brown
paste, which was extracted with pentane. The resulting
solution was washed with 0.5% aqueous sodium bicar-
bonate, dried over MgSO4, and evaporated.
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