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