Facile generation of [bis(2-pyridyldimethylsilyl)methyl]lithium and its reaction with carbonyl compounds. New method for the stereoselective synthesis of vinylsilanes

Article abstract of DOI:10.1016/S0040-4020(01)00348-9

The generation of (2-PyMe₂Si)₂CHLi was easily accomplished by the deprotonation of (2-PyMe₂Si)₂CH₂ using n-BuLi in Et₂O. The ¹H NMR analysis of (2-PyMe₂Si)₂CHLi in Et₂O-d₁₀ revealed the coordination of both pyridyl groups to lithium. Thus generated (2-PyMe₂Si)₂CHLi was found to react with a variety of aldehydes and ketones to give the corresponding vinylsilanes in extremely high yields with complete stereoselectivities (>99% E).

Full text of DOI:10.1016/S0040-4020(01)00348-9

TETRAHEDRON
Pergamon
Tetrahedron 57 ,2001) 5045±5054
Facile generation of [bisꢀ2-pyridyldimethylsilyl)methyl]lithium
and its reaction with carbonyl compounds. New method for the
stereoselective synthesis of vinylsilanes
Kenichiro Itami, Toshiki Nokami and Jun-ichi Yoshidap
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Kyoto 606-8501, Japan
Dedicated to Professor Barry M. Trost on the occasion of his 60th birthday
Received 19 January 2001; revised 2 February 2001; accepted 5 February 2001
AbstractÐThe generation of ,2-PyMe2Si)2CHLi was easily accomplished by the deprotonation of ,2-PyMe2Si)2CH2 using n-BuLi in Et2O.
The H NMR analysis of ,2-PyMe2Si)2CHLi in Et2O-d10 revealed the coordination of both pyridyl groups to lithium. Thus generated
1
,2-PyMe2Si)2CHLi was found to react with a variety of aldehydes and ketones to give the corresponding vinylsilanes in extremely high
yields with complete stereoselectivities ,.99% E). q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
the intermediacy of b-silyl alkoxide or b-silyl alcohol.2 The
interesting aspect of the Peterson-type ole®nation is that
the course of the reaction is highly dependent on the sub-
stituents on a-carbon. In the case of the reaction of a-silyl
carbanions bearing alkyl, hydrogen, or electron-donating
substituents on a-carbon, b-silyl alcohols are usually
isolated.2 Treatment of thus isolated b-silyl alcohols with
The Peterson-type ole®nation reaction has emerged as an
extremely useful method for the preparation of alkenes from
carbonyl compounds.1,2 Although the exact mechanism of
the Peterson-type ole®nation is not clear at the present time,
it has been generally accepted that the reaction occurs with
Scheme 1. Two types of reaction modes of Peterson-type ole®nation.
Keywords: Peterson-type ole®nation reaction; vinylsilanes; silyl alcohols.
Corresponding author. Tel.: 181-75-753-5651; fax: 181-75-753-5911; e-mail: yoshida@sbchem.kyoto-u.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020,01)00348-9

5046
K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
Scheme 2. Complex induced proximity effect in the deprotonation of 2.
acid or base leads to the formation of alkenes ,Scheme 1).3,4
The bene®t of this procedure is that the stereoselectivity
,E or Z) can be controlled by the choice between acid and
base. On the other hand, the reaction of a-silyl carbanions
bearing aryl or electron-withdrawing group on a-carbon
leads to the direct formation of alkenes, in which the initial
intermediate undergoes spontaneous elimination reaction
,Scheme 1).2 In this case, the stereoselectivity of the reac-
tion is dependent on the steric and electronic nature of
the substituents on a-carbon and silicon.2 By using the
Peterson-type ole®nation reaction, synthetically useful
vinylsilanes can be prepared by the reaction of bis,silyl)-
methylmetal with carbonyl compounds using the later direct
addition/elimination process.4±6
In ongoing efforts to exploit 2-PyMe2Si group in the a-silyl
carbanion chemistry, we envisioned that appending mul-
tiple 2-PyMe2Si groups should lead to interesting reactivity.
Recently, we reported the facile deprotonation of
,2-PyMe2Si)2CH2 and the reaction of thus generated
,2-PyMe2Si)2CHLi with carbonyl compounds, which leads
to the stereoselective synthesis of vinylsilanes.13 In this
paper, we report on the full details of this study.
2. Results and discussion
2.1. Deprotonation of bisꢀ2-pyridyldimethylsilyl)-
methane
The synthesis of starting material ,2-PyMe2Si)2CH2 ,2)
can be easily accomplished in one-pot by the reaction of
2-PyMe2SiCH2Li, which is easily generated by the deproto-
nation of 2-pyridyltrimethylsilane 1 with 2-PyMe2SiH as
reported previously ,Eq. ,2)).11
Despite many practical advantages of Peterson-type ole-
®nation reactions over the conventional carbonyl ole®nation
reactions,7 such as Wittig reaction, Tebbe reaction, Nozaki
reaction, and Julia coupling, there exist several signi®cant
disadvantages to be overcome before the Peterson-type
ole®nation becomes to be enlisted into service in a real
sense. For example, there is no general route for the gener-
ation of a-silyl carbanion and this chemistry still suffers
from its substrate dependence.8
Recently, we have embarked on a program directed towards
the development of a general method for the generation of
synthetically useful a-silyl carbanion. We paid particular
attention to the silane deprotonation methodology because
of its convenience compared with the other a-silyl carb-
anion-generating methods such as metal±halogen exchange
reaction, metal±heteroatom exchange reaction, and alkyl-
lithium±vinylsilane addition reaction.8 Our approach was
to append the potentially coordinating pyridyl group on sili-
con thereby enabling the facile deprotonation. For example,
the facile deprotonation of otherwise dif®cult methyl group
on silicon9 was achieved by utilizing pyridyl group as
the intramolecular ligand ,Eq. ,1)).10±12 Thus generated
2-PyMe2SiCH2Li was found to be an excellent nucleophilic
hydroxymethylating reagent for various electrophiles.11
ꢀ2†
At the outset, we examined the deprotonation of 2 to gener-
ate ,2-PyMe2Si)2CHLi ,3). We have already reported that
the deprotonation of 1 is highly dependent on the lithiating
agent employed: t-BuLi leads to quantitative deprotonation;
n-BuLi leads to a complex mixture.10 As in the case for 1,
the deprotonation of 2 was successfully accomplished by
1.1 equiv. of t-BuLi in Et2O at 2788C and subsequent reac-
tion with allyl bromide gave the corresponding adduct
ꢀ1†
Figure 1. 1H NMR of 3 in Et2O-d10 at 2788C.

K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
5047
to the subsequent deprotonation ,Scheme 2). As a result, the
formation of the pre-equilibrium complex renders the
deprotonation event intramolecular in nature and this
might be the reason for the increased reactivity of 2.
In addition to the kinetic preference for the deprotonation of
2 by CIPE, we presume that the thermodynamic stabili-
zation of generated organolithium 3 by the intramolecular
pyridyl group coordination is also responsible for the ef®-
ciency of this deprotonation process. In order to ascertain
whether the pyridyl group is coordinating to lithium or not,
1
we next examined the structure of 3 in solution using H
NMR spectroscopy in Et2O-d10 at 2788C ,Fig. 1). The H
1
NMR spectrum showed two singlets ,0.20 and 0.21 ppm)
due to the two methyl groups on each silicon atom and one
singlet ,21.39 ppm) due to a proton on a-carbon. The
observed non-equivalence of the methyl groups on silicon
is most likely attributed to the coordination induced rigid
®ve-membered cyclic structure of 3. Moreover, the
observed two singlets indicate that both pyridyl groups are
coordinating to the lithium and that the two 2-PyMe2Si
groups are equivalent. In line with these assumptions, two
Figure 2. 1H NMR of methyl groups on silicon of 3 in Et2O-d10: ,a) at
2788C; ,b) raised to 2308C from 2788C; ,c) raised to 08C from 2308C;
,d) re-cooled to 2308C from 08C; ,e) re-cooled to 2788C from 308C.
1
pyridyl groups were equivalent in the H NMR spectrum
,see Section 4).
Next, we examined the variable-temperature 1H NMR
experiments for 3 at intervals of 15 min ,raising: 278,
230, 08C; re-cooling: 0, 230, 2788C) ,Fig. 2). It was
found that the two singlets for the methyl groups on silicon
coalesced at 08C ,Fig. 2c), which implies that the ring
¯ipping of 5-membered cyclic structure becomes rapid
around 08C. In addition, re-cooling of the sample to
2788C ,Fig. 2e) showed identical spectrum with the origi-
nal one ,Fig. 2a), which indicates the reasonable stability of
3 at 08C.
,2-PyMe2Si)2CHCH2CHvCH2 ,4) in 82% yield ,Eq. ,3)).
Anticipating the increased reactivity of 2, we next employed
n-BuLi under otherwise identical conditions and 4 was
isolated in 92% yield ,Eq. ,3)). Simple alkyl bromides
were not applicable as electrophiles in this reaction because
of their lower reactivities toward nucleophiles. We assume
that the steric hindrance of 3 is also responsible for its low
reactivity toward alkyl bromides, since 2-PyMe2SiCH2Li
possesses suf®cient reactivity toward various alkyl bro-
mides.11
2.2. Reaction of [bisꢀ2-pyridyldimethylsilyl)methyl]-
lithium with carbonyl compounds
Having established the facile deprotonation of 2, we further
investigated the reactions of ,2-PyMe2Si)2CHLi ,3) with
various carbonyl compounds. It has been reported that the
reactions of 2-PyMe2SiCH2Li with aldehydes and ketones
gave the b-silyl alcohols without formation of alkenes by
the Peterson-type elimination.11 However, in the case of 3,
the Peterson-type ole®nation was found to take place, after
or concurrently with the addition, to give the corresponding
vinylsilanes 5 stereoselectively. The results are depicted in
Table 1.
ꢀ3†
The realization of extremely ef®cient deprotonation of 2
under very mild conditions might be worth mentioning.
As already reported by several groups, the deprotonation
of ,Me3Si)2CH24,14 or related bis,silyl)methane15,16 requires
very forcing conditions such as t-BuLi/THF/HMPA/
2408C/7.5 h4 or n-BuLi/TMEDA/rt/1 week.14 On the
other hand, in the case of 2, the deprotonation does not
require t-BuLi or polar solvent system. These results clearly
suggest the enhanced reactivity of 2 toward base. We
assume that the deprotonation of 2 proceeded through the
agency of what Beak and Meyers have termed `complex
induced proximity effect ,CIPE)'.17 In the reaction, there
must be a pre-equilibrium complex of 2 and n-BuLi prior
The reactions with primary, secondary, and tertiary aliphatic
and aromatic aldehydes gave the corresponding vinylsilanes
in quantitative yields ,entries 1±7). Noteworthy is that the
reaction is also applicable to the sterically hindered alde-
hydes ,entries 3 and 6) and bis-aldehyde ,entry 7). Ketones
gave the disubstituted vinylsilanes with somewhat lower
yields ,entries 8±10). For enolizable ketones such as
acetophenone, proton transfer presumably competed with
addition where 3 serves as the base ,entry 9). The reaction
can be applied to the stereoselective synthesis of dienyl-
silanes as well ,entries 11±13). In all cases, virtually
complete stereoselectivities ,.99% E) were observed.

5048
K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
Table 1. Reactions of ,2-PyMe2Si)2CHLi with carbonyl compoundsa
a
Unless otherwise noted, the reactions were performed in dry Et2O using 3 and carbonyl compounds ,1.5 equiv.) at 2788C for 30 min and then room
temperature for 1 h under argon.
Isolated yields based on 3.
b
c
Determined by 1H, 13C NMR analysis, and NOE experiments.
The reaction was performed using 3 ,2.5 equiv) and carbonyl compound ,1.0 equiv).
d

K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
5049
Scheme 3. Two reaction modes in the Peterson-type synthesis of vinylsilane.
2.3. The origin of stereoselectivity
additive led to vinylsilane with very high stereoselectivities
,E/Zˆ92/8±99/1). He concluded that b-silyl alkoxide is not
a major intermediate in the direct addition/elimination
sequences and suggested that the reaction of bis,silyl)-
methyllithium and aldehydes may involve nearly simul-
taneous formation of C±C and Si±O bonds to give
oxasiletane anion directly. Consistent with these results,
many reported direct addition/elimination reactions of
bis,silyl)methylmetal and carbonyl compounds lead to the
formation of vinylsilanes with lower E selectivities.6
It has been well documented that the acid- or base-mediated
elimination from the isolated b-silyl alcohol is highly
stereoselective.3 However, this is not the case for the direct
addition/elimination sequences. Hudrlik has elegantly
revealed this somewhat puzzling phenomenon ,Scheme
3).4 For example, consistent with the original report by
Seebach,5 the condensation of ,Me3Si)2CHLi with benz-
aldehyde gave vinylsilane with a mixture of stereoisomers
,E/Zˆ58/42).18 On the other hand, the treatment of
the isolated b-silyl alcohol with a variety of bases and
However, we observed complete E-selectivity in the direct
Figure 3. The origin of stereoselectivity.

5050
K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
Scheme 4. Synthetic transformations of 2-pyridyl-substituted vinylsilanes.
addition/elimination reaction of ,2-PyMe2Si)2CHLi with
various carbonyl compounds. To the best of our knowledge,
this is the ®rst general method for the stereoselective syn-
thesis of vinylsilane, which proceeds with direct addition/
elimination sequences. If the selectivities are governed by
the well-accepted syn-elimination from the b-silyl alkoxide
,A or B),2 the selectivity differences between ,2-PyMe2Si)2-
CHLi and ,Me3Si)2CHLi should not be dramatic as it is
,Fig. 3). Moreover, Hudrlik has already established that
the use of more sterically demanding t-BuMe2Si group
instead of Me3Si group only led to a slight increase in the
E selectivity, indicating that the steric factor is not a sole
decisive factor for the high selectivity.4 There must be some
contributions of pyridyl group in the observed high stereo-
selectivity. We surmise that, before the elimination of the
siloxy group, the chair-like conformer ,C or D) might be
involved as a stereo-determining intermediate where the
intramolecular coordination of the pyridyl group locks the
conformation.19 Of the two, D should be preferred over C,
since both silyl and RL groups can occupy the equatorial
positions. Thus, preferred conformer D may lead to the
observed E-isomer. However, we must stress that these
discussions are purely speculative with no experimental
evidence.
,ii) greater electrophilicity of 2-PyMe2Si group renders the
alkoxide attack more readily.15
ꢀ4†
2.5. Synthetic transformations of 2-pyridyl-substituted
vinylsilanes
We conducted several synthetic transformations of 2-pyri-
dyl-substituted vinylsilanes 5 that we prepared ,Scheme 4).
Subjection of 2-pyridyl-substituted vinylsilanes into the
action of KF/MeOH led to the formation of methoxy,vinyl)-
silane by 2-Py±Si bond cleavage.12b The resultant methoxy-
silane can be further allowed to react with Grignard reagents
such as PhMgBr to give the corresponding vinylsilane that
can be used for further transformations.20
2.4. Elimination aptitude of 2-PyMe2Si group
In order to assess the elimination aptitude of the 2-PyMe2Si
group in the Peterson-type ole®nation, we next conducted
the control experiment using 2-PyMe2SiCH2SiMe2Ph ,6)
that can be prepared in 99% yield by the reaction of
2-PyMe2SiCH2Li with PhMe2SiCl. The generation of
2-PyMe2SiCH,Li)SiMe2Ph was successfully accomplished
by the reaction of 6 with t-BuLi in Et2O. Thus generated
carbanion was subsequently allowed to react with benz-
aldehyde to give the PhMe2Si-substituted styrene 7 in
95% yield ,Eq. ,4)). The formation of a 1/1 mixture of
two stereoisomers ,E and Z) strongly denotes that the
addition process is non-selective giving the two diastereo-
meric intermediates. Moreover, it should be noted that the
formation of 2-PyMe2Si-substitued styrene was not detected
at all in this reaction. This observation underscores greater
elimination aptitude of 2-PyMe2Si group and we assume the
following as the plausible explanations: ,i) the coordination
of pyridyl group may force the conformation as in C or D
,Fig. 3), thereby making 2-PyMe2Si group to eliminate; and
More practically, 2-pyridyl-substituted vinylsilane itself can
be directly subjected to the reactions with various electro-
philes. For example, treatment of 5d with CH3COCl in the
presence of AlCl3 afforded 4-phenyl-3-buten-2-one in 91%
yield. Bromination of 5d afforded b-bromostyrene in 54%
yield.
3. Conclusions
In conclusion, we have established that ,2-PyMe2Si)2CH2
undergoes extremely facile deprotonation by n-BuLi to
give ,2-PyMe2Si)2CHLi quantitatively. The 1H NMR analy-
sis of ,2-PyMe2Si)2CHLi in Et2O-d10 revealed the coordi-
nation of both pyridyl groups to lithium. Thus generated
,2-PyMe2Si)2CHLi was found to react with a variety of
aldehydes and ketones affording the corresponding vinyl-
silanes and dienylsilanes in extremely high yields with
complete stereoselectivities ,.99% E). This expeditious

K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
5051
and versatile protocol will ®nd use in many organic reac-
tions using vinylsilanes and dienylsilanes.20
NaOH pellet and was extracted with Et2O ,2£10 mL).
Drying over MgSO4 and removal of the solvents under
reduced pressure afforded 3 ,63 mg, 92%) as a pale yellow
oil: 1H NMR ,300 MHz): d 0.21 ,s, 6H), 0.28 ,s, 6H), 0.86
,t, Jˆ6.0 Hz, 1H), 2.26±2.34 ,m, 2H), 4.67 ,ddt, Jˆ9.9, 1.8,
1.5 Hz, 1H), 4.72 ,ddt, Jˆ16.8, 1.8, 1.5 Hz, 1H), 5.55 ,ddt,
Jˆ16.8, 9.9, 6.9 Hz, 1H), 7.09 ,ddd, Jˆ7.5, 4.8, 1.5 Hz,
2H), 7.37 ,ddd, Jˆ7.5, 1.5, 1.2 Hz, 2H), 7.46 ,td, Jˆ7.5,
1.5 Hz, 2H), 8.69 ,ddd, Jˆ4.8, 1.5, 1.2 Hz, 2H); 13C NMR
,75 MHz): d 22.6, 22.1, 10.9, 30.2, 113.8, 122.5, 129.2,
133.7, 140.7, 149.9, 168.3. HRMS m/z calcd for
C18H26N2Si2: 326.1635; found: 326.1635.
4. Experimental
4.1. General
NMR spectra were recorded on Varian GEMINI-2000 ,1H
300 MHz, 13C 75 MHz) and JEOL A-500 ,1H 500 MHz, 13
C
125 MHz) spectrometers in CDCl3 with internal standards
,7.26 ppm 1H, 77.0 ppm 13C). Mass spectra ,EI) were
recorded with a JMS-SX102A spectrometer. Infrared spec-
tra were recorded on a Shimadzu FTIR-8100 spectrophoto-
meter. Gel permeation chromatography was carried out with
Japan Analytical Industry LC-918. Unless otherwise noted,
all materials were obtained from commercial suppliers and
used without further puri®cation. Diethyl ether ,Et2O) was
freshly distilled under argon from sodium benzophenone
ketyl prior to use.
4.2. General procedure for the synthesis of vinylsilanes
ꢀ5)
To a solution of 2 ,143 mg, 0.5 mmol) in dry Et2O ,1 mL)
was added dropwise a solution of n-BuLi ,0.55 mmol,
1.50 M in hexane) at 2788C. After being stirred for an
additional 1 h, a carbonyl compound ,0.75 mmol) was
added and the mixture was stirred for 30 min at 2788C
and 1 h at room temperature. The reaction was quenched
with a saturated aqueous solution of NH4Cl. Extractive
work-up and subsequent silica gel chromatography ,hexane/
EtOAcˆ10/1 to 5/1 as eluent) afforded vinylsilanes 5.
Yields are given in Table 1.
4.1.1. Bisꢀ2-pyridyldimethylsilyl)methane ꢀ2). To a solu-
tion of 2-pyridyltrimethylsilane 1 ,6.13 g, 40.5 mmol) in dry
Et2O ,40 mL) was added dropwise a solution of t-BuLi
,40.0 mmol, 1.38 M solution in pentane) at 2788C. The
mixture was stirred for additional 30 min. To the resultant
solution of ,2-pyridyldimethylsilyl)methyllithium was
added a solution of 2-pyridyldimethylsilane ,5.49 g,
40.0 mmol) in dry Et2O ,20 mL) at 2788C and stirred for
30 min. After stirring the reaction mixture at room tempera-
ture for 12 h, the reaction was quenched with a saturated
aqueous solution of NH4Cl. Extractive work-up and subse-
quent distillation afforded 2 ,5.99 g, 52%) as colorless oil:
bp 1278C/0.15 mmHg. 1H NMR ,300 MHz) d 0.22 ,s, 12H),
0.38 ,s, 2H), 7.08 ,ddd, Jˆ7.5, 4.8, 1.5 Hz, 2H), 7.38 ,ddd,
Jˆ7.5, 1.5, 1.2 Hz, 2H), 7.46 ,td, Jˆ7.5, 1.8 Hz, 2H), 8.68
,ddd, Jˆ4.8, 1.8, 1.2 Hz, 2H); 13C NMR ,75 MHz) d 21.2,
0.1, 122.5, 128.6, 133.8, 150.0, 168.7. IR ,neat) 2955, 1576,
1559, 1451, 1418, 1248, 1051 cm21. Anal. Calcd for
C15H22N2Si2: C, 62.88; H, 7.74; N, 9.78. Found: C, 62.61;
H, 7.78; N, 9.79. HRMS m/z calcd for C14H19N2Si2
,M2CH3)1: 271.1087; found: 271.1079.
4.2.1. ꢀE)-2-Pyridyldimethylꢀ4-phenyl-1-butenyl)silane
ꢀ5a). H NMR ,300 MHz) d 0.38 ,s, 6H), 2.43±2.53 ,m,
1
2H), 2.70±2.79 ,m, 2H), 5.86 ,dt, Jˆ18.6, 1.5 Hz, 1H),
6.24 ,dt, Jˆ18.6, 6.3 Hz, 1H), 7.14±7.22 ,m, 4H), 7.24±
7.31 ,m, 2H), 7.44 ,ddd, Jˆ7.5, 1.5, 0.9 Hz, 1H), 7.56 ,td,
Jˆ7.5, 1.8 Hz, 1H), 8.79 ,ddd, Jˆ4.8, 1.8, 0.9 Hz, 1H); 13C
NMR ,75 MHz) d 23.3, 34.9, 38.4, 122.8, 125.8, 127.3,
128.3, 128.5, 129.5, 134.0, 141.9, 148.9, 150.3, 167.5.
HRMS m/z calcd for C17H21NSi: 267.1443; found: 267.1431.
4.2.2. ꢀE)-2-Pyridyldimethylꢀ2-cyclohexylethenyl)silane
ꢀ5b). H NMR ,300 MHz) d 0.36 ,s, 6H), 1.00±1.35 ,m,
1
5H), 1.58±1.80 ,m, 5H), 1.94±2.08 ,m, 1H), 5.75 ,dd,
Jˆ18.9, 1.2 Hz, 1H), 6.13 ,dd, Jˆ18.9, 5.7 Hz, 1H), 7.16
,ddd, Jˆ7.5, 4.8, 1.8 Hz, 1H), 7.50 ,ddd, Jˆ7.5, 1.8, 1.2 Hz,
1H), 7.55 ,td, Jˆ7.5, 1.8 Hz, 1H), 8.77 ,ddd, Jˆ4.8, 1.8,
1.2 Hz, 1H); 13C NMR ,75 MHz) d 23.3, 25.9, 26.1, 32.2,
43.9, 122.7, 123.1, 129.4, 133.9, 150.3, 155.5, 167.9. IR
,neat) 2924, 1612, 1574, 1449, 1418, 1244 cm21. HRMS
m/z calcd for C15H23NSi: 245.1600; found: 245.1604.
4.1.2. [Bisꢀ2-pyridyldimethylsilyl)methyl]lithium ꢀ3). To
a solution of 2 ,14.5 mg, 0.05 mmol) in dry Et2O ,0.2 mL)
and Et2O-d10 ,0.3 mL) was added dropwise a solution of n-
BuLi ,0.06 mmol, 1.56 M solution in hexane) at 2788C.
The mixture was left for additional 30 min to afford an
orange ether solution of [bis,2-pyridyldimethylsilyl)-
4.2.3.
ꢀE)-2-Pyridyldimethylꢀ3,3-dimethylbut-1-enyl)-
1
1
methyl]lithium ,3). H NMR ,500 MHz, Et2O-d10, 2788C)
silane ꢀ5c). H NMR ,300 MHz) d 0.38 ,s, 6H), 1.01 ,s,
9H), 5.71 ,d, Jˆ18.9 Hz, 1H), 6.18 ,d, Jˆ18.9 Hz, 1H),
7.18 ,ddd, Jˆ7.5, 4.8, 1.5 Hz, 1H), 7.48 ,dt, Jˆ7.5,
1.2 Hz, 1H), 7.57 ,td, Jˆ7.5, 1.8 Hz, 1H), 8.78 ,dm, Jˆ
4.8 Hz, 1H); 13C NMR ,75 MHz) d 23.2, 28.9, 35.2,
119.6, 122.7, 129.5, 134.1, 150.2, 160.3, 167.9. HRMS
m/z calcd for C13H20NSi ,M2H)1: 218.1365; found:
218.1368.
d 21.39 ,s, 1H), 0.20 ,s, 6H), 0.21 ,s, 6H), 7.26 ,ddd, Jˆ7.5,
5.0, 1.0 Hz, 2H), 7.60 ,dd, Jˆ7.5, 1.0 Hz, 2H), 7.68 ,td, Jˆ
7.5, 1.0 Hz, 2H), 8.69 ,dd, Jˆ5.0, 1.0 Hz, 2H).
4.1.3. 4,4-Bisꢀ2-pyridyldimethylsilyl)butene ꢀ4). To a
solution of 2 ,60 mg, 0.21 mmol) in dry Et2O ,1 mL) was
added dropwise a solution of n-BuLi ,0.23 mmol, 1.55 M in
hexane) at 2788C. After stirring for an additional 1 h, allyl
bromide ,38 mg, 0.31 mmol) was added and stirred for 1 h
at 08C. After being stirred at room temperature for 17 h, the
mixture was washed with H2O ,2£10 mL). The organic
phase was additionally extracted with 1N aq HCl ,3£
10 mL). The aqueous phase was basi®ed to pH 14 by adding
1
4.2.4. ꢀE)-2-Pyridyldimethylstyrylsilane ꢀ5d). H NMR
,300 MHz) d 0.50 ,s, 6H), 6.65 ,d, Jˆ19.2 Hz, 1H), 7.02
,d, Jˆ19.2 Hz, 1H), 7.21 ,ddd, Jˆ6.9, 4.8, 2.1 Hz, 1H),
7.26±7.36 ,m, 3H), 7.44±7.49 ,m, 2H), 7.54±7.62 ,m,
2H), 8.81 ,dt, Jˆ5.1, 1.2 Hz, 1H); 13C NMR ,75 MHz) d

5052
K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
1
23.4, 122.9, 126.1, 126.6, 128.3, 128.6, 129.5, 134.1, 138.2,
145.9, 150.4, 167.0. IR ,neat) 2959, 1605, 1574, 1495,
1449, 1418, 1246 cm21. HRMS m/z calcd for C15H17NSi:
239.1131; found: 239.1122.
ꢀ5k). H NMR ,300 MHz) d 0.42 ,s, 6H), 5.15 ,ddd, Jˆ
9.9, 1.5, 0.6 Hz, 1H), 5.25 ,ddd, Jˆ16.8, 1.5, 0.6 Hz, 1H),
6.05 ,dd, Jˆ18.3, 0.9 Hz, 1H), 6.39 ,dtd, Jˆ16.8, 9.9,
0.9 Hz, 1H), 6.64 ,ddt, Jˆ18.3, 9.9, 0.6 Hz, 1H), 7.18
,ddd, Jˆ7.5, 4.8, 1.8 Hz, 1H), 7.50 ,ddd, Jˆ7.5, 1.8,
1.2 Hz, 1H), 7.57 ,td, Jˆ7.5, 1.8 Hz, 1H), 8.78 ,ddd, Jˆ
4.8, 1.8, 1.2 Hz, 1H); 13C NMR ,75 MHz) d 23.5, 118.6,
122.9, 129.5, 131.2, 134.1, 139.7, 146.8, 150.4, 167.0. IR
,neat) 2959, 1574, 1256 cm21. Anal. Calcd for C11H15NSi:
C, 69.78; H, 7.99; N, 7.40. Found: C, 69.69; H, 8.17; N,
7.37. HRMS m/z calcd for C11H15NSi: 189.0974, found
189.0977.
4.2.5. ꢀE)-2-Pyridyldimethylꢀ2-furan-2-ylethenyl)silane
1
ꢀ5e). H NMR ,300 MHz) d 0.47 ,s, 6H), 6.30 ,d, Jˆ
3.3 Hz, 1H), 6.37 ,dd, Jˆ3.3, 1.8 Hz, 1H), 6.48 ,d, Jˆ
18.9 Hz, 1H), 6.79 ,d, Jˆ18.9 Hz, 1H), 7.19 ,ddd, Jˆ7.2,
4.8, 2.1 Hz, 1H), 7.36 ,d, Jˆ1.8 Hz, 1H), 7.51±7.62 ,m,
2H), 8.79 ,dm, Jˆ4.8 Hz, 1H); 13C NMR ,75 MHz) d
23.4, 108.7, 111.5, 122.9, 124.1, 129.6, 133.2, 134.1,
142.5, 150.4, 154.0, 166.8. IR ,neat) 2959, 1617, 1576,
1545, 1478, 1417, 1248 cm21. HRMS m/z calcd for
C13H15NOSi: 229.0923, found 229.0927.
4.2.12. ꢀE,E)-2-Pyridyldimethylꢀ3-methylbuta-1,3-dienyl)-
silane ꢀ5l). 1H NMR ,300 MHz) d 0.43 ,s, 6H), 1.86 ,s, 3H),
5.04 ,d, Jˆ1.5 Hz, 1H), 5.09 ,d, Jˆ1.5 Hz, 1H), 6.00 ,d,
Jˆ18.9 Hz, 1H), 6.74 ,d, Jˆ18.9 Hz, 1H), 7.19 ,ddd, Jˆ7.5,
4.8, 1.8 Hz, 1H), 7.51 ,ddd, Jˆ7.5, 1.8, 1.2 Hz, 1H), 7.58
,td, Jˆ7.5, 1.8 Hz, 1H), 8.79 ,ddd, Jˆ4.8, 1.8, 1.2 Hz, 1H);
13C NMR ,75 MHz) d 23.4, 17.8, 118.0, 122.8, 125.9,
129.5, 134.0, 143.5, 148.8, 150.3, 167.2. IR ,neat) 2988,
1576, 1246 cm21. HRMS m/z calcd for C12H17NSi:
203.1130; found: 203.1121.
4.2.6. ꢀE)-2-Pyridyldimethyl[2-ꢀ2,4,6-trimethylphenyl)-
ethenyl]silane ꢀ5f). H NMR ,300 MHz) d 0.52 ,s, 6H),
1
2.28 ,s, 3H), 2.29 ,s, 6H), 6.12 ,d, Jˆ19.8 Hz, 1H), 6.87
,s, 2H), 7.04 ,d, Jˆ19.8 Hz, 1H), 7.17±7.25 ,m, 1H), 7.56±
7.62 ,m, 2H), 8.81 ,dt, Jˆ4.8, 1.2 Hz, 1H); 13C NMR
,75 MHz) d 23.3, 20.6, 20.8, 122.8, 128.7, 129.5, 132.3,
134.0, 135.4, 136.2, 136.3, 144.9, 150.3, 167.3. HRMS m/z
calcd for C18H23NSi: 281.1600, found 281.1591.
4.2.13. ꢀE,E)-2-Pyridyldimethylꢀ4-phenylbuta-1,3-dienyl)-
silane ꢀ5m). 1H NMR ,300 MHz) d 0.46 ,s, 6H), 6.16 ,dm,
Jˆ17.1 Hz, 1H), 6.60 ,dt, Jˆ14.7, 6.0 Hz, 1H), 6.76±6.89
,m, 2H), 7.19±7.26 ,m, 2H), 7.29±7.34 ,m, 2H), 7.38±7.42
,m, 2H), 7.54 ,ddd, Jˆ7.5, 1.5, 1.2 Hz, 1H), 7.60 ,td, Jˆ7.5,
1.5 Hz, 1H), 8.80 ,ddd, Jˆ5.4, 1.8, 1.2 Hz, 1H); 13C NMR
,75 MHz) d 23.3, 122.7, 126.5, 127.7, 128.5, 129.3, 131.0,
131.3, 133.6, 133.9, 136.9, 146.1, 150.1, 166.7. IR ,neat)
2956, 1576, 1246, 1001 cm21. HRMS m/z calcd for
C17H19NSi: 265.1287; found: 265.1291.
4.2.7. ꢀE,E)-Bis{1,4-[2-ꢀ2-pyridyldimethylsilyl)ethenyl]}-
benzene ꢀ5g). 1H NMR ,300 MHz) d 0.49 ,s, 12H), 6.64 ,d,
Jˆ19.2 Hz, 2H), 6.99 ,d, Jˆ19.2 Hz, 2H), 7.17±7.24 ,m,
2H), 7.43 ,s, 4H), 7.52±7.63 ,m, 4H), 8.80 ,dm, Jˆ5.1 Hz,
2H); 13C NMR ,75 MHz) d 23.4, 122.9, 126.3, 126.8,
129.5, 134.1, 138.0, 145.4, 150.3, 166.9. IR ,KBr) 1603,
1574, 1557, 1509, 1451, 1420, 1248 cm21. HRMS m/z
calcd for C24H28N2Si2: 400.1791; found: 400.1793.
4.2.8. 2-Pyridyldimethylꢀ2-methylpropenyl)silane ꢀ5h).
1H NMR ,300 MHz) d 0.40 ,s, 6H), 1.72 ,s, 3H), 1.88 ,d,
Jˆ1.5 Hz, 3H), 5.41 ,br, 1H), 7.17 ,ddd, Jˆ7.5, 4.8, 1.8 Hz,
1H), 7.50±7.60 ,m, 2H), 8.78 ,dm, Jˆ4.8 Hz, 1H); 13C
NMR ,75 MHz) d 21.8, 23.6, 29.4, 121.1, 122.6, 129.3,
134.0, 150.3, 154.6, 168.3. HRMS m/z calcd for
C11H17NSi: 191.1130; found: 191.1139.
The E stereochemistry of 5 was assigned based on the NOE
experiments and the coupling constants between the two
1
vinylic protons ,17.1±19.8 Hz) in H NMR. The selected
NOE data are as follows:
4.2.9.
ꢀE)-2-Pyridyldimethylꢀ2-phenylpropenyl)silane
1
ꢀ5i). H NMR ,300 MHz) d 0.52 ,s, 6H), 2.17 ,d, Jˆ
0.6 Hz, 3H), 6.12 ,d, Jˆ0.6 Hz, 1H), 7.19±7.24 ,m, 1H),
7.28±7.35 ,m, 3H), 7.50 ,dt, Jˆ6.9, 1.8 Hz, 2H), 7.59 ,dt,
Jˆ4.5, 1.2 Hz, 2H), 8.81 ,dt, Jˆ4.8, 1.5 Hz, 1H); 13C NMR
,75 MHz) d 21.8, 21.4, 122.8, 124.0, 125.6, 127.7, 128.2,
129.5, 134.2, 144.0, 150.3, 154.0, 167.7. IR ,neat) 3061,
2959, 1597, 1574, 1493, 1445, 1418, 1246, 1138 cm21
.
HRMS m/z calcd for C16H19NSi: 253.1287; found: 253.1284.
4.2.10. 2-Pyridyldimethylꢀ2,2-diphenylethenyl)silane ꢀ5j).
1H NMR ,300 MHz) d 0.16 ,s, 6H), 6.55 ,s, 1H), 7.10±7.19
,m, 3H), 7.22±7.36 ,m, 8H), 7.37±7.45 ,m, 1H), 7.53 ,td,
Jˆ7.5, 1.8 Hz, 1H), 8.78 ,dm, Jˆ5.1 Hz, 1H); 13C NMR
,125 MHz) d 22.0, 122.5, 126.34, 126.35, 127.3, 127.4,
127.8, 128.0, 129.3, 129.6, 133.9, 142.3, 142.9, 150.0,
158.8, 167.8. IR ,neat) 3058, 2957, 1574, 1489, 1443,
1418, 1246 cm21. HRMS m/z calcd for C21H21NSi:
315.1443; found: 315.1444.
4.2.14. 2-Pyridyldimethyl[ꢀphenyldimethylsilyl)methyl]-
silane ꢀ6). To a solution of 2-pyridyltrimethylsilane 1
,3.03 g, 20 mmol) in dry Et2O ,20 mL) was added dropwise
a solution of tert-butyllithium ,20 mmol, 1.31 M solution in
pentane) at 2788C. The mixture was stirred for additional
4.2.11. ꢀE,E)-2-Pyridyldimethylꢀbuta-1,3-dienyl)silane

K. Itami et al. / Tetrahedron 57 +2001) 5045±5054
5053
30 min. To the resultant solution of ,2-pyridyldimethyl-
silyl)methyllithium was added chlorodimethylphenylsilane
,3.76 g, 22 mmol) at 2788C and the mixture was stirred for
1 h. After stirring for 3 h at room temperature, the reaction
was quenched with H2O ,20 mL). Extractive work-up and
subsequent silica gel chromatography ,hexane/EtOAcˆ10/
solvents were removed under reduced pressure to give the
crude 1,2-dibromide. The crude 1,2-dibromide was dis-
solved in ice-cold MeOH ,5 mL) and treated with NaOMe
,41 mg, 0.75 mmol) in MeOH ,0.75 mL) at 08C. The result-
ing mixture was stirred at 08C for 1 h and then at room
temperature for 12 h. Extractive work-up and subsequent
silica gel chromatography ,hexane as eluent) afforded
b-bromostyrene ,40 mg, 54%, E/Zˆ67/33) as colorless oil.
1
1 as eluent) afforded 6 ,5.64 g, 99%) as colorless oil: H
NMR ,300 MHz) d 0.23 ,s, 6H), 0.27 ,s, 6H), 0.35 ,s, 2H),
7.16 ,ddd, Jˆ7.5, 4.8, 1.5 Hz, 1H), 7.29±7.33 ,m, 3H),
7.42±7.49 ,m, 3H), 7.54 ,td, Jˆ7.5, 1.8 Hz, 1H), 8.76
,ddd, Jˆ4.8, 1.8, 1.2 Hz, 1H); 13C NMR ,75 MHz) d
21.1, 20.5, 1.1, 122.6, 127.7, 128.68, 128.71, 133.4,
134.0, 140.9, 150.1, 168.9. IR ,neat) 3067, 2955, 1576,
1559, 1428, 1248, 1113 cm21. HRMS m/z calcd for
C16H23NSi2: 285.1369; found: 285.1358.
Acknowledgements
This research was supported by a Grant-in-Aid for Scienti®c
Research from the Ministry of Education, Science,
Sports and Culture, Japan, and in part by the Mitsubishi
Foundation.
4.2.15. 1-Phenyl-2-ꢀdimethylphenylsilyl)ethylene ꢀ7). To
a solution of 6 ,294 mg, 1.03 mmol) in dry Et2O ,1 mL) was
added dropwise a solution of t-BuLi ,1.10 mmol, 1.31 M in
pentane) at 2788C and the mixture was stirred for 30 min.
To the resultant solution of carbanion was added benz-
aldehyde ,127 mg, 1.20 mmol) at 2788C and the mixture
was stirred for 30 min. After stirring overnight at room
temperature, the reaction was quenched with H2O ,5 mL).
Extractive work-up and subsequent silica gel chroma-
tography ,hexane as eluent) afforded 7 ,234 mg, 95%) as
a mixture of stereoisomers ,E/Zˆ1/1). These isomers were
separated by gel permeation chromatography. E-isomer:21
1H NMR ,300 MHz) d 0.46 ,s, 6H), 6.61 ,d, Jˆ18.9 Hz,
1H), 6.97 ,d, Jˆ18.9 Hz, 1H), 7.27±7.40 ,m, 6H), 7.47 ,d,
Jˆ6.9 Hz, 2H), 7.58±7.62 ,m, 2H); 13C NMR ,75 MHz) d
22.7, 126.6, 127.1, 127.9, 128.2, 128.6, 129.1, 134.0, 138.2,
138.6, 145.4; IR ,neat) 3067, 3022, 2957, 1605, 1574, 1495,
1248, 1113, 990 cm21. Z-isomer:21 1H NMR ,300 MHz) d
0.26 ,d, Jˆ0.6 Hz, 6H), 6.01 ,d, Jˆ15.0 Hz, 1H), 7.22 ,s,
5H), 7.32±7.36 ,m, 3H), 7.50 ,d, Jˆ15.0 Hz, 1H), 7.52±
7.57 ,m, 2H); 13C NMR ,75 MHz) d 21.1, 127.4, 127.8
,two peaks as judged by integration), 128.2, 128.8, 130.2,
133.7, 139.58, 139.61, 148.1; IR ,neat) 2961, 1592, 1570,
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