The stereoselective synthesis of conjugated allylsilanes

Article abstract of DOI:10.1080/10426500600616589

2-trimethylsilylethylidenetriphenylphosphorane (5) (Seyferth-Wittig reagent) reacts stereoselectively with the carbonyl compounds 6a-f to give the conjugated allylsilanes 7a-f, each as a mixture of E-and Z-isomers. The stereoselectivity of reactions of E-

Full text of DOI:10.1080/10426500600616589

Phosphorus, Sulfur, and Silicon, 181:2283–2295, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500600616589
The Stereoselective Synthesis of Conjugated Allylsilanes
Mohamed Refat H. Mahran
Hisham Abdallah A. Yosef
Department of Organometallic and Organometalloid Chemistry,
National Research Centre, Dokki, Cairo, Egypt
Franz Effenberger
Institute of Organic Chemistry, Stuttgart University, Stuttgart,
Germany
2-trimethylsilylethylidenetriphenylphosphorane (5) (Seyferth–Wittig reagent) re-
acts stereoselectively with the carbonyl compounds 6a–f to give the conjugated
allylsilanes 7a–f, each as a mixture of E-and Z-isomers. The stereoselectivity of
reactions of E-cinnamaldehyde (6c) with 5 has been investigated at different tem-
peratures. A successful E-stereoselective synthesis of 7c was achieved by reacting
5 with E-cinnamaldehyde (6c) under the conditions of a Wittig–Schlosser mod-
ification reaction. Structures of the allylsilanes 7a–f were deduced by compatible
1
13
analytical and spectroscopic (IR, H NMR, C NMR, and GC/MS) measurements.
1
An assignment of the E:Z ratios of 7a–f is based on their H NMR spectral data.
Keywords Allylsilanes; Seyferth–Wittig reagents; structure elucidation; Wittig–
Schlosser modification
INTRODUCTION
Since allylsilanes hold a tremendous potential as reagents and inter-
mediates in the field of preparative organic chemistry,2,3 there has
been a relentless and continuing search for methods4−8 for the prepa-
ration of a diverse range of simple and functionalized allylsilanes. A
Received September 15, 2005; accepted January 19, 2006.
This work is considered as “Organophosphorus Chemistry 35” for part 34. cf. ref. 1.
H. A. A. Yosef is grateful to the German Academic Exchange Service for the award of a
fellowship, and M. R. H. Mahran is profoundly indebted to the Alexander von Humboldt-
Stiftung (Federal Republic of Germany) for the generous donation of HPLC Equipment
(Perkin-Elmer, system 1022, model 135 C).
Address correspondence to Franz Effenberger, Institute of Organic Chemistry,
Stuttgart University, Pfaffenwaldring 55, Stuttgart, D-70569 Germany. E-mail: franz.
effenberger@oc.uni-stuttgart.de
2283

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M. R. H. Mahran et al.
relatively straightforward synthetic route to a wide variety of allylsi-
lanes is the Wittig reaction of 2-silyl phosphorus ylides with carbonyl
compounds,4,5,9 which was introduced by Seyferth et al.4 and then mod-
ified by Fleming and Paterson.5 The stereoselectivity of the reaction and
subsequently the stereochemistry of the alkenes prepared are highly
influenced by the ylide structure, nature of the carbonyl reactant, and
experimental conditions.10−12
Very few studies9,13−15 have been devoted to the stereoselectiv-
ity of the Wittig reaction of 2-silylphosphoranes with carbonyl com-
pounds. Some studies16,17 have given a boost to the preparation of
stereo-homogeneous allylsilanes for the stereoregulated synthesis of
acyclic systems. In the present work, use is made of the Wittig–
Schlosser modification12,18−20 for the synthesis of stereochemically pure
E-allylsilane derivatives.
RESULTS AND DISCUSSION
The Synthesis of the Conjugated Allylsilanes 7a–f via
a Wittig Reaction
By following Fleming’s one-pot procedure,5 the conjugated carbonyl
compounds 6a–f with exclusive E-configuration were allowed to re-
act with 2-trimethylsilylethylidenetriphenylphosphorane (5) to give the
corresponding allylsilanes 7a–f (Scheme 1). Combined GC/MS21 mea-
surements indicate that 7a–f were isolated as mixtures of E and Z
isomers. The E:Z ratios of compounds 7a–f (Table I) were determined
1
by a quantitative analysis of their H NMR spectral data.7,8,22 1H-1H
COSY NMR spectra of the new allylsilanes 7d–f have provided helpful
information to define the protons that belong to each isomer as well
as to elucidate the connectivity of the carbon atoms to which the pro-
tons are attached for each individual isomer.22 The IR frequencies23 as
well as the 13C-NMR chemical shifts24 of 7a–f have also given valuable
information in confirming their structures.
Table I summarizes the results of the synthesis of conjugated allylsi-
lanes by a reaction of the corresponding aldehydes 6 with the reactive
triphenylphosphorane 5, following Fleming’s one-pot procedure.
Z-selectivity occurs in the obtained allylsilanes 7a–d. It is evident
that 5 reacts with the unsaturated aldehydes 6a–d to provide the allyl-
silanes 7a–d with a higher proportion of Z-isomer (Table I) as expected
in reactions of the un-stabilized triphenylphosphorus ylides (e.g., 5)
with aldehydes.10,11,26 The Z-stereoselectivity is not very high, which
may be attributable to the facile reversibility of the reactions with aro-
matic and α, β-unsaturated aldehydes.27

The Stereoselective Synthesis of Conjugated Allylsilanes
2285
TABLE I Isomer Ratios and Yields of the
Allylsilanes 7a–f
7
E:Z Ratio
Yield (%)
a
b
cb
d
e
22:78
33:67
29:71
23:77
89:11
77:23
13.9a
29.8
66.1
71.3
62.9
49.9
f
a
The low yield may be attributed to the low b.p. and
the loss during the chromatographic process and
evaporation of eluent; cf. ref. 7 and 8.
bCf. ref. 9 and 25.
SCHEME 1

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M. R. H. Mahran et al.
SCHEME 2
Though compounds 7a,b are known, they are now prepared for the
first time by applying the Wittig reaction as a simple and direct sub-
stitute for other approaches, which are indirect ones.7,8 Compound 7c
has been prepared previously also via a Wittig reaction by two differ-
ent groups.9,25 Ylide 5 reacts also with the conjugated ketones 6e,f but
with an inverted stereoselectivity compared to its reactions with alde-
hydes 6a–d (Table I). The allylsilane 7d is not yet described in the
literature. Its structure is proved by GC/MS analysis, IR, as well as
1
by 13C and mainly HNMR spectroscopy (see Experimental section).
The methylene protons adjacent to the trimethylsilyl group of 7d are
expected to be deshielded when oriented cis (Z-isomer) to the C4-C5
double bond, due to its anisotropy, rather than when oriented trans (E-
isomer).7,8 Thus, they resonate in the 1H NMR spectrum (using CHCl3
as an internal standard) at δ = 1.49 ppm (d, J1−H,2−H = 8.4 Hz) for the
E-isomer and at δ = 1.63 ppm (d, J1−H,2−H = 8.9 Hz) for the Z-isomer.
Similarly, the two singlets at δ = 0.00 and 0.01 ppm were attributed to
the shielded CH3-protons of SiMe3 in the E- and Z-isomer, respectively.
The doublet of triplets centered at δ = 5.35 ppm is attributed to the C2-
proton of the Z-isomer, while that of the E-isomer appears deshielded at
δ = 5.48 ppm due to the anisotropy of the C4-C5 double bond. This esti-
mation is supported by the 1H-1H COSY NMR spectrum of 7d wherein
signals appearing at δ = 5.35 and 5.48 ppm show cross peaks to the
doublets that appeared at δ = 1.63 and 1.49 ppm, respectively. The E:Z
SCHEME 3

The Stereoselective Synthesis of Conjugated Allylsilanes
2287
ratio of 23:77 was confirmed also by an evaluation of the integral levels
of the methylene protons adjacent to the trimethylsilyl group. As al-
ready mentioned, the dominant isomers of 7e and 7f are the E-isomers,
which have the CH2-SiMe3 and CH3 groups oriented Z to each other,
exhibit E:Z ratios of 89:11 and 77:23, respectively (see spectral data in
the Experimental section).
The E:Z ratio of allylsilane 7e, taken as an example, was determined
1
mainly via the H NMR spectrum. It shows two singlets at δ = 0.00
and 0.01 ppm (CHCl3 as an internal standard) due to an absorption
of the SiMe3 protons of the E- and Z-isomer, respectively. The doublet
centered at δ = 1.63 ppm is attributed to the absorption of the methy-
lene protons adjacent to the SiMe3 group of the E-isomer, and the dou-
blet centered at δ = 1.69 ppm (3J1−H,2−H = 9.8 Hz) is attributed to the
Z-isomer. Moreover, the olefinic proton C CH CH2 is responsible for
the two triplets appearing at δ = 5.49 (3J2−H,1−H = 9.8 Hz) and 5.69 ppm
(3J2−H,1−H = 9.0 Hz) belonging to the Z- and E-isomer, respectively.
The Temperature Dependence of the Reactions of Ylide 5 with
E-Cinnamaldehyde (6c)
To investigate the effect of reaction conditions (e.g., temperature)
on the stereoselectivity of the reactions with 2-silyl phosphorus ylides,
E-cinnamaldehyde (6c) was reacted with 2-trimethylsilylethylidene-
triphenylphosphorane (5) at different temperatures (Table II).
At −78◦C the reaction was found to be Z-stereoselective yielding the
allylsilane 7c in an E:Z ratio of 29:71. When the THF solution of 6c was
added to 5 at 0◦C, the reaction became nonstereoselective (an E:Z ratio
of 48:52). A further increase of the reaction temperature had almost no
effect any more (Table II).
For an incorporation of conjugated allylsilanes into self-assembled
monolayers, we were mainly interested in the preparation of all-E
TABLE II Stereoselectivity of the Reaction
of Ylide 5 With E-Cinnamaldehyde (6c) at
Different Temperatures
Reaction
Allylsilane 7c
Temperature
(◦C)
E:Z(%)a
Yield%
−78
0
22
67
29:71
48:52
52:48
53:47
66.1
52.0
72.8
43.0
aE:Z ratios were determined from 1H NMR data.

2288
M. R. H. Mahran et al.
conjugated allylsilanes. We therefore investigated the Wittig–Schlosser
modification of the olefination.
The Trans-Stereoselective Synthesis of a Conjugated
Allylsilane by Applying A Wittig–Schlosser Modification
The stereochemical outcome of Wittig-reactions under various reaction
conditions and strucural factors has been discussed and explained in
many reports.10,11,26,27 In an attempt to prepare an allylsilane with
a predominant E-configuration, we have now applied the Wittig–
Schlosser modification12,18−20 on the reaction of ylide 5 with E-
cinnamaldehyde (6c) at different reaction conditions (e.g., solvent
and/or base) (Schemes 4 and 5).
SCHEME 4
SCHEME 5
In an attempt to optimize the E-isomer ratio of 7c, reaction condi-
tions described by Schlosser et al.18,20 and Schlosser and Christmann19
have been followed. Thus, 2-trimethylsilylethyl-triphenylphosphonium
iodide (4) was first prepared and isolated as described by Seyferth et al.4
The treatment of a suspension of 4 in a 5:3 (v/v) solvent mixture of
THF/Et2O with phenyllithium/Et2O20 affords ylide 5, which reacts in
situ with 6c (Scheme 5). After the usual workup, allylsilane 7c was
1
isolated in an E:Z ratio of 98:2 as determined from the H-NMR spec-
trum. All 1H and 13CNMR signals that correspond to the Z-isomer have
almost disappeared.

The Stereoselective Synthesis of Conjugated Allylsilanes
2289
CONCLUSION
From the results presented, it could be demonstrated that the re-
action of 2-silyl phosphorus ylides (e.g., 5) with conjugated carbonyl
compounds (e.g., 6a–f) can be successfully applied for the synthesis of
conjugated allylsilanes (e.g., 7a–f). This approach contributes highly
to the synthetic potential of the Wittig reactions since allylsilanes are
very useful reagents and intermediates in the field of synthetic organic
chemistry.2,3 The reactions of ylide 5 with the carbonyl compounds 6a–f
following Fleming’s one-pot procedure were found to be nonstereoselec-
tive at r.t. and becoming more Z-selective at lower temperatures. The
Wittig–Schlosser modification, however, can be applied successfully in
the reaction of 2-silyl phosphorus ylides (e.g., 5) with aldehydes (e.g.,
6c) in order to prepare stereoselectively almost pure E-allylsilanes. Ap-
plying the experimental conditions described by Schlosser using a self-
prepared phenyllithium containing soluble lithium bromide resulted in
an almost exclusive formation of all-E 7c.
EXPERIMENTAL
All reactions were carried out in flame-dried glassware under an at-
mosphere of dry nitrogen or argon. Solvents were rigorously dried: di-
ethyl ether and THF by distillation from sodium in the presence of
benzophenone (sodium diphenylketyl) under an atmosphere of dry ni-
trogen, and petroleum ether by fractional distillation. Standard syringe
techniques were applied for the transfer of bases and dry solvents as
well as solutions of the reacting carbonyl compounds. Reacting aldehy-
des 6a–d were distilled directly before use. Carbonyl compounds 6b–f
were pure E-isomers (1H and 13C NMR spectra). Isolated allylsilanes
7a–f were stored at −15◦C. Pure compounds were isolated by liquid
chromatography using columns with different sizes packed with silica
gel 60 (0.040–0.063 mm) (Merck) after an elution with the appropriate
solvent. Infrared spectra were obtained from CDCl3 solutions using a
Perkin Elmer Printer 283 spectrophotometer and are reported in cm−1
.
1H NMR spectra as well as 1H-1H COSY NMR spectra were measured
using a Brucker AC 250F spectrometer operating at 250 MHz. Proton
chemical shifts (δ) are reported in ppm downfield from TMS; CDCl3 was
used as a solvent and CHCl3 as an internal standard at δ = 7.25 ppm
downfield from TMS. 13C NMR spectra were recorded on a Bruker AC
250F instrument operating at 63 MHz. Chemical shifts (δ) are given in
ppm downfield from TMS and referenced to the central peak of CDCl3
at δ = 77.0 ppm. Mass spectra were recorded with a Finnigan 4500
GC/MS spectrometer at 70 eV. Gas-liquid chromatography and HPLC

2290
M. R. H. Mahran et al.
were used for purity control and the detection of geometrical isomers
using Hewlett Packard 5700A and Hewlett Packard 5890 seriesII with
autoinjector 7673 instruments. MS measurements were carried out us-
ing electron impact ionization (electron energy = 70 eV) for compounds
7a,d,e or chemical ionization using methane as a reactant gas for com-
pounds 7b,c,f.
The Synthesis of the Conjugated Allylsilanes 7a–f via a Wittig
Reaction: General Procedure5
n-BuLi (1.6 molar solution in hexane) was added dropwise with stirring
over 0.5 h to a suspension of methyltriphenylphosphonium bromide (1)
in abs. THF at 0◦C under dry nitrogen. The ice bath was removed,
and the mixture was warmed to r.t. (ca. 0.5 h) and stirred for 1 h to
give a yellow solution of methylenetriphenylphosphorane (2). The re-
action mixture was recooled to 0◦C, and iodomethyltrimethylsilane (3)
was added over 10 min. The mixture was allowed again to come slowly
to r.t. (ca. 0.5 h) when 2-trimethylsilylethyltriphenylphosphonium io-
dide (4) precipitated. After 1 h, the reaction mixture was treated with
a second mole equivalent of n-BuLi at −78◦C. The cooling bath was
removed, and the mixture was allowed to warm slowly to r.t. (ca. 1
h) and stirred for a further 1.5 h to give a dark red solution of 2-
trimethylsilylethylidenetriphenyl-phosphorane (5). The carbonyl com-
pound 6 in abs. THF was then added dropwise over 15 min to the ylide
solution at –78◦C under nitrogen. After 0.5 h, the cooling bath was re-
moved, and the reaction mixture was allowed to warm slowly to r.t.,
and stirred under nitrogen for 16 h, quenched by pouring onto satu-
rated ammonium chloride solution and extracted with diethyl ether.
The organic extract was dried (MgSO4) and evaporated in vacuo. Al-
lylsilanes 7a–f were isolated by column chromatography on silica gel
after an elution with CCl4 for 7a,b and with petroleum ether for 7c–f
(Table III). The experimental data for the synthesis of the allylsilanes
7a–f are summarized in Table III.
1-(Trimethylsilylmethyl)-4-propyl-1,3-butadiene (7d)
Colorless oil (1.30 g, 71.3%; E:Z 23:77). Calcd. for C11H22Si (182.38): C,
72.44; H, 12.16. Found: C, 72.30; H, 12.27. IR (CDCl3, cm−1): 3000 (m,
ν
C H alkene); 2940 (vs, νas CH3); 2905 (s, νas CH2); 2880 (s, νs CH3);
2855 (s, νs CH2); 1595 (w, ν C C alkene); 1410 (w, δas CH3 on Si); 1235
(s, δs CH3 on Si); 970 (s, δ CH CH trans out-of-plane def.); 840 (vs), 760
(w) (CH3 on Si rocking vib.); 650 (w, νas Si C); 580 (w, νs Si C).
1H NMR (CDCl3, δ): 0.00 [s, 9H, Si(CH3)3, E-isomer]; 0.01 [s, 9H,
3
Si(CH3)3, Z-isomer]; 0.89 [t, J8,7 = 7.3 Hz, 3H, 8-H, E-isomer]; 0.90

2291

2292
M. R. H. Mahran et al.
[t, 3J8,7 = 7.3 Hz, 3H, 8-H, Z-isomer]; 1.32–1.46 [m, 4H, 7-H, E- and Z-
isomers]; 1.49 [d, 3J1,2 = 8.4 Hz, 2H, 1-H, E-isomer]; 1.63 [d, 3J1,2 = 8.9
Hz, 2H, 1-H, Z-isomer]; 1.98–2.11 [m, 4H, 6-H, E- and Z-isomers]; 5.35
[dt, 3J2,1 = 8.9 Hz, 3J2,3 = 10.8 Hz, 1H, 2-H, Z-isomer]; 5.48 [dt, 3J2,1
=
3
3
8.4 Hz, J2,3 = 13.6 Hz, 1H, 2-H, E-isomer]; 5.56 [dt, J5,4 = 14.6 Hz,
3J5,6 = 7.6 Hz, 1H, 5-H, E-isomer]; 5.60 [dt, 3J5,4 = 15.0 Hz, 3J5,6 = 7.0
3
3
Hz, 1H, 5-H, Z-isomer]; 5.87 [dd, J3,2 = 13.6 Hz, J3,4 = 10.1 Hz, 1H,
3
3-H, E-isomer]; 5.89 [t, J3,2 = 10.8 Hz, 1H, 3-H, Z-isomer); 5.99 [dd,
3J4,3 = 10.1 Hz, J4,5 = 14.6 Hz, 1H, 4-H, E-isomer); 6.24 [dd, J4,3
=
3
3
11.0 Hz, 3J4,5 = 15.0 Hz, 1H, 4-H, Z-isomer).
13C NMR (CDCl3,δ): −1.9 [Si(CH3)3, E-isomer]; -1.7 [Si(CH3)3, Z-
isomer]; 12.7 [C8, E-isomer]; 13.7 [C8, Z-isomer]; 19.3 [C1, Z-isomer];
19.8 (C7, E-isomer); 22.7 (C7, Z-isomer); 23.4 (C1, E-isomer); 34.8 [C6,
E-isomer); 35.0 (C6, Z-isomer); 126.0, 126.2, 126.5, 128.8, 129.3, 130.3,
130.8, 133.0 (C2, C3, C4, C5, E− and Z-isomers).
GC/EIMS [70 eV, m/z (relative abundance %)], E-isomer: 182 (1.8)
[M]+, 109 (< 1) [M − SiMe3]+, 108 (2.4) [M – (SiMe3 + H)]+, 73 (100)
[SiMe3]+; Z-isomer: 182 (2.6) [M]+, 109 (<1) [M − SiMe3]+, 108 (2.6)
[M − (SiMe3+ H]+, 73 (100) [SiMe3]+.
1-(Trimethylsilylmethyl)-2-methyl-4-phenyl-1,3-butadiene (7e).
White waxy solid (2.90 g, 62.9%; E:Z 89:11), m.p. 32–34◦C. Calcd.
for C15H22Si ( 230.42): C, 78.19; H, 9.62. Found: C, 78.18; H, 9.77. IR
(CDCl3, cm−1): 3060 (w), 3040 (w) ( ν C H arom); 3010 (m, ν C H
alkene); 2940 (s, νas C H satd.); 2870 (m, νs C H satd.); 1620 (m, ν C C
alkene); 1590 (m), 1485 (m) ( ν C C arom); 1405 (w, δas CH3 on Si); 1240
(s, δs CH3 on Si); 945 (s, δ CH CH trans out-of-plane def.); 840 (vs), 765
(w) (CH3 on Si rocking vib.); 650 (w, νas Si C); 595 (w, νs Si C);
1H NMR (CDCl3, δ): 0.00 [s, 9H, Si(CH3)3, E-isomer]; 0.01 [s, 9H,
3
Si(CH3)3, Z-isomer]; 1.63 [d, J1,2=9.0 Hz, 2H, 1-H, E-isomer]; 1.69
3
4
[d, J1,2 = 9.8 Hz, 2H, 1-H, Z-isomer]; 1.78 [d, J6,2 = 0.6 Hz, 3H,
4
6-H, E-isomer]; 1.91 [d, J6,2 = 1.1 Hz, 3H, 6-H, Z-isomer]; 5.49 [t,
3J2,1 = 9.8 Hz, 1H, 2-H, Z-isomer]; 5.69 [t, J2,1 = 9.0 Hz, 1H, 2-H,
3
E-isomer]; 6.33 [d, 3J5,4 = 16.0 Hz, 1H, 5-H, E-isomer]; 6.46 [d, 3J5,4
=
16.0 Hz, 1H, 5-H, Z-isomer]; 6.79 [d, 3J4,5 = 16.0 Hz, 1H, 4-H, E-isomer];
7.08-7.37 [m, 11H, 4-H of Z-isomer and aromatic protons of E- and
Z-isomers].
13C NMR (CDCl3, δ): –1.5 [Si(CH3)3, E- and Z-isomers); 12.4 [C10, E-
isomer); 19.4 [C1, Z-isomer]; 20.4 [C10, Z-isomer]; 20.6 (C1, E-isomer);
124.0, 126.1, 126.4, 126.6, 127.0, 128.6, 131.3, 134.6 [C2, C4, C5, C7,
C8, C9, E- and Z-isomers]; 129.8 (C3, Z-isomer); 131.7 [C3, E-isomer];
138.4 (C6, E- and Z-isomers).

The Stereoselective Synthesis of Conjugated Allylsilanes
2293
GC/EIMS [70 eV, m/z (relative abundance %)], E-isomer: 230 (4.1)
[M]+·, 157 (<1) [M-·SiMe3]+, 156 (1.1) [M-(·SiMe3−·H]+·, 143 (1.1) [M −
·CH2SiMe3]+, 73 (100) [SiMe3]+, Z-isomer: 230 (2.9) [M]+·, 157 (<1) [M
- ·SiMe3]+, 156 (<1) [M – (·SiMe3−·H)]+·, 143 (<1) [M − ·CH2SiMe3]+,
73 (100) [SiMe3]+.
1-(Trimethylsilylmethyl)-2-methyl-4-(2-furyl)-1,3-butadiene (7f)
Yellow oil (1.10 g, 49.9%; E:Z 77:23). Calcd. for C13H20OSi (220.39):
C, 70.85; H, 9.15. Found: C, 71.31; H, 9.21. IR (CDCl3, cm−1): 3100 (w, ν
C H furan ring); 3030 (w, ν C H alkene); 2940 (m, νas C H satd.);
2870 (w, νs C H satd.); 1610 (m, ν C C alkene); 1550 (w), 1480 (w) (ν
C C furan ring); 1405 (w, δas CH3 on Si); 1240 (s, δs CH3 on Si); 940 (s,
δ CH CH transout-of-plane def.); 840 (vs), 775 (w) (CH3 on Si rocking
vib.); 650 (w, νas Si C); 575 (w, νs Si C).
1H NMR (CDCl3, δ): 0.00 [s, 9H, Si(CH3)3, E-isomer]; 0.01 [s, 9H,
3
Si(CH3)3, Z-isomer]; 1.63 [d, J1,2 = 9.0 Hz, 2H, 1-H, E-isomer]; 1.69
3
4
[d, J1,2 = 9.2 Hz, 2H, 1-H, Z-isomer]; 1.73 [d, J10,2 = 0.5 Hz, 3H,
4
10-H, E-isomer]; 1.86 [d, J10,2 = 1.0 Hz, 3H, 10-H, Z-isomer]; 5.49 [t,
3J2,1 = 9.2 Hz, 1H, 2-H, Z-isomer]; 5.7 [t, J2,1 = 9.0 Hz, 1H, 2-H, E-
3
isomer]; 6.15 [d, 3J5,4 = 16.0 Hz, 1H, 5-H, E-isomer]; 6.16 [d, 3J7,8 = 3.3
3
Hz, 1H, 7-H, E-isomer]; 6.21 [d, J7,8 = 3.5 Hz, 1H, 7-H, Z-isomer];
3
3
6.27 [d, J5,4 = 15.9 Hz, 1H, 5-H, Z-isomer]; 6.34 [dd, J8,7 = 3.3 Hz,
3J8,9 = 1.8 Hz, 1H, 8-H, E-isomer]; 6.36 [dd, 3J8,7 = 3.5 Hz, 3J8,9 = 1.6
3
Hz, 1H, 8-H, Z-isomer]; 6.75 [d, J4,5 = 16.0 Hz, 1H, 4-H, E-isomer];
7.04 [d, 3J4,5 = 15.9 Hz, 1H, 4-H, Z-isomer]; 7.29 [d, 3J9,8 = 1.8 Hz, 1H,
9-H, E-isomer]; 7.33 [d, 3J9,8 = 1.6 Hz, 1H, 9-H, Z-isomer].
13C NMR (CDCl3, δ): –1.58 [Si(CH3)3, Z-isomer]; -1.55 [Si(CH3)3, E-
isomer]; 12.0 [C10, E-isomer]; 19.4 [C1, Z-isomer]; 20.3 [C10, Z-isomer];
20.7 (C1, E-isomer); 106.4 (C7, E-isomer); 107.3 (C7, Z-isomer); 111.46
(C8, E-isomer); 111.52 (C8, Z-isomer); 112.3 [C5, E-isomer]; 115.1 [C5,
Z-isomer]; 129.4 [C3, Z-isomer]; 131.3 (C3, E-isomer); 125.0, 129.0,
131.5, 133.3 (C2, C4, E- and Z-isomers); 141.2 (C9, E-isomer); 141.6
(C9, Z-isomer); 154.3 (C6, E- and Z-isomers).
GC/EIMS [70 eV, m/z (relative abundance %)], E-isomer: 221 (100)
[MH]+, 220 (74.2) [M]+·, 205 (63.9) [M − ·CH3]+, 147 (5.2) [M − ·SiMe3]+,
73 (29.9) [SiMe3]+, Z-isomer: 221 (100) [MH]+; 220 (92.6) [M]+·, 205
(96.8) [M − ·CH3]+, 147 (4.2) [M − ·SiMe3]+, 73 (32.6) [SiMe3]+.
The Synthesis of all-E Allylsilane 7c by Applying the Schlosser
Modification of the Wittig Reaction
Starting from Methyltriphenylphosphonium Bromide (1)
Ylide 5 was prepared as described in the general procedure from 1
(4.02 g, 11.25 mmol), n-BuLi (7.8 mL, 12.5 mmol), and 3 (2.41 g, 11.25

2294
M. R. H. Mahran et al.
mmol) in THF (20 mL). Then a solution of E-cinnamaldehyde (6c) (1.32
g, 10 mmol) in abs. THF (5 mL) was added to the ylide solution at
−78◦C within 5 min under a dry N2 atmosphere. After decoloration
of the reaction mixture (5 min), an additional amount of n-BuLi (6.3
mL of 1.6 molar solution in hexane, 10 mmol) was added at – 78◦C to
give the dark red solution of the β-oxidophosphonium ylide (betaine
ylide). The reaction mixture was vigorously stirred while the tempera-
ture was being raised gradually to −35◦C (25 min), then ethereal HCl
(11 mL of 1N HCl in 20 mL of diethyl ether) was added, causing an
immediate decolouration. After an addition of potassium tert-butoxide
(1.7 g, 15 mmol), the mixture was allowed to warm slowly to r.t., stirred
for further 2 h, quenched by pouring onto saturated ammonium chlo-
ride solution (50 mL), and extracted with diethyl ether (3 × 150 mL).
The combined organic extracts were dried (MgSO4) and evaporated in
vacuo. The residue was chromatographed on silica gel with petroleum
ether to give the allylsilane 7c in a 47.6% yield, and the E:Z ratio =
72:28.
Starting from 2-trimethylsilylethyltriphenylphosphonium
Iodide (4)
Phenyllithium (4 mL of 1.5 molar solution, 6 mmol) in Et2O
was added dropwise with stirring over 0.5 h to a suspension of 2-
trimethylsilyl-ethyltriphenylphosphonium iodide (4),4 prepared by re-
acting iodo-methyltrimethylsilane (3) with a freshly prepared solution
of methylene-triphenylphosphorane (2)28 (2.9 g, 6 mmol) in a solvent
mixture of abs. THF (10 mL) and abs. diethyl ether (6 mL) at −78◦C
under dry nitrogen. The mixture was allowed to warm slowly to r.t. (1
h) and stirred for further 2 h to give the dark red-colored solution of 2-
trimethylsilyl-ethylidenetriphenylphosphorane (5). The reaction mix-
ture was cooled again to −78◦C, and a solution of E-cinnamaldehyde
(6c) (0.8 g, 6 mmol) in abs. diethyl ether (3 mL) was added over 2 min.
After decolouration of the reaction mixture (5 min), an additional mole
equivalent of PhLi (4 mL of 1.5 molar solution, 6 mmol) was added
at −78◦C to give the dark red solution of β-oxidophosphonium ylide
(betaine ylide). The reaction mixture was vigorously stirred while the
temperature was raised gradually to −35◦C (25 min), then ethereal HCl
(7 mL of 1N HCl in 15 mL of Et2O) was added causing an immediate
decolouration. After an addition of potassium tert-butoxide (1.01 g, 9
mmol), the mixture was allowed to warm slowly to r.t. and then stirred
for a further 2 h, quenched by pouring onto saturated ammonium chlo-
ride solution (30 mL) and extracted with diethyl ether (3 × 100 mL).
The combined organic extracts were dried (MgSO4) and evaporated in
vacuo. The residue was chromatographed on silica gel with petroleum

The Stereoselective Synthesis of Conjugated Allylsilanes
2295
ether to give the allylsilane 7c as almost exclusively the E-isomer (E:Z
ratio = 98:2) in a 42.4 % yield.
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