Allylsilanes

4.4.40.40 Method 40:
Formation of 3-Substituted Allylsilanes by a Peterson-type Elimination
Regio- and stereodefined 3-substituted allylsilanes have been prepared by Peterson-type
elimination reaction of ul-1,2-bis(trimethylsilyl)alkan-3-ols; the base-induced reaction
gives the Z-isomer, and the acid-catalyzed reaction gives the E-isomer in over 95% stereochemical
purityin most cases. [57,226] For example, the E-3-substituted allyltrimethylsilanes
(E)-163 have been obtained byacid-catalyzed elimination of 162, whereas potassium hydride
induced reaction of 162 gives the corresponding Z-isomers (Z)-163 (Scheme
64). [57,226] Desilylation products, that is, E- and Z-1-phenylpropenes form with potassium
hydride only in the case of 163 (R 1 = Ph); this problem can be obviated byuse of sodium
hydride in place of potassium hydride. [226] The desired bis-silylated alcohols 162 have
been prepared either from Z-vinylsilanes via the corresponding epoxides and opening of
the latter [226] with an á-silylated organocuprate, or from (E)-1,3-bis(trimethylsilyl)propene
via the corresponding epoxide and reaction of the latter [57] with a Gilman reagent.
Scheme 64 Formation of 3-Substituted Allylsilanes by a Peterson-type Elimination [57,226]
HO
H
R1 162
SiMe3 H
SiMe 3
FOR PERSONAL USE ONLY
886 Science of Synthesis 4.4 Silicon Compounds
BF3 OEt2
R1 = Me 99% (GC)
R1 = iPr 96% (GC)
R1 = Bu 92%
R 1
SiMe 3
KH R 1 SiMe3
R1 = Me 92% (GC)
R1 = iPr 97% (GC)
R1 = Bu 85%
(E)-163
(Z)-163
[(Z)-Hept-2-enyl]trimethylsilane [(Z)-163,R 1 = Bu]; Typical Procedure: [226]
Commercial 35% KH in mineral oil (1.14 g) was washed with pentane (3 ” 15 mL) and dried
under a stream of N 2. To this was added THF (20 mL), and, to the stirred slurry, 162
(R 1 = Bu) (2.6 g, 10 mmol) was added dropwise bysyringe. After 1 h at 308C, the mixture
was centrifuged and the decanted soln was poured into a separating funnel containing a
mixture of sat. aq NH 4Cl (50 mL) and Et 2O (50 mL). After separation, the organic material
was dried (K 2CO 3), concentrated in vacuo, and distilled; yield: 1.5 g (85%); bp 888C/55 Torr.
[(E)-Hept-2-enyl]trimethylsilane [(E)-163, R 1 = Bu]; Typical Procedure: [226]
BF 3 ·OEt 2 (0.47 g, 3.3 mmol) was added dropwise to a stirred soln of 162 (R 1 = Bu) (2.6 g,
10 mmol) in CH 2Cl 2 (20 mL) at 08C. After 15 min, the soln was poured into a separating
funnel containing sat. aq NaHCO 3 (50 mL). After separation, the organic material was
washed with sat. aq NaHCO 3 (2 ” 50 mL), dried (K 2CO 3), concentrated in vacuo, and distilled;
yield: 1.57 g (92%); bp 888C/55 Torr.
4.4.40.41 Method 41:
Formation of 3-Substituted Allylsilanes by Silicon-Directed
Bamford±Stevens Reaction
3-Substituted allylsilanes are available from â-silyl ketones via the corresponding Naziridinylimines
by a silicon-directed Bamford±Stevens reaction of the latter. Thus, thermolysis
of â-trimethylsilyl N-aziridinylimines 165 in toluene in the presence of rhodium(II)
acetate (2 mol%) at 1458C gives allylsilanes 166 containing a major proportion of
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG