Allylsilanes

1-tert-Butyl-1-vinylcyclohexane (218); Typical Procedure: [98]
TiCl 4 (1.04 g, 5.5 mmol) was added to CH 2Cl 2 (5 mL) and the soln was cooled to ±788C with
stirring. This cooled soln was transferred by syringe to a stirred soln of allylsilane 46
(910 mg, 5 mmol) and t-BuCl (0.65 mL, 6 mmol) in CH 2Cl 2, precooled to ±78 8C. After 1 h,
the mixture was poured into sat. NaHCO 3 (25 mL), extracted with Et 2O (3 ” 50 mL), dried,
and concentrated. The residue was purified bychromatographyor distillation; yield:
813 mg (98%).
4.4.40.57 Method 57:
Radical Allylation of Alkyl Halides
Radical allylation of alkyl halides with 2-substituted allyltris(trimethylsilyl)silanes 158,
preparation of which is described in Section 4.4.40.38, takes place under mild conditions
and in good yields (Scheme 84). [41] Unlike allylation reactions of allylstannanes, these reactions
are subject to polar effects, in that, while electrophilic radicals add smoothlyto
electron-rich acceptors, nucleophilic radicals prefer electron-poor acceptors as partners;
this is illustrated, for example, bythe respective syntheses of alkenes 220 and 221 from
silane 158 (Scheme 84). [41]
Scheme 84 Allylation with Allyltris(trimethylsilyl)silanes [41]
O
O
220
O
FOR PERSONAL USE ONLY
4.4.40 Allylsilanes 903
O
Br
AIBN, benzene
reflux, 6 h
R 1 = H 87%
R 1
Si(SiMe 3) 3
158
(t-BuO)2
R 1 = CO 2Me 75%
I
221
CO 2Me
3-Allyldihydrofuran-2-one (220); Typical Procedure: [41]
Allyltris(trimethylsilyl)silane (158, R 1 = H; 1.05 g, 3.63 mmol) and AIBN (0.020 g,
0.12 mmol) were added consecutivelyto a magneticallystirred, degassed soln of 3-bromodihydrofuran-2-one
(0.2 g, 1.21 mmol) in benzene (6 mL) under argon. The mixture was
maintained at reflux, and additional AIBN (0.020 g, 0.12 mmol) was added everyhour.
The reaction was monitored byTLC or GC until the starting material was consumed
(6 h); the reaction mixture was then worked up bypassage through a short column (silica
gel, Et 2O/pentane 2:1). After the silyl material had eluted in the first fraction, the product
was collected; yield: 132 mg (87%).
4.4.40.58 Method 58:
Addition to Epoxides and Oxetanes
Oxiranes react with allylsilanes under Lewis acid promotion to give functionalized pentenols,
for example, pent-4-en-1-ol 222 from silane 46 (Scheme 85). [20,21,30,98] Extension of
this methodologyfor the preparation of hexenols is possible. For example, treatment of
prenylsilane 10, available bythe method of synthesis discussed in Section 4.4.40.1, with
oxetane gives hex-5-en-1-ol 223. [133]
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
for references see p 920