Allylsilanes

Scheme 30 Allylsilanes by Palladium(0)-Catalyzed Carbosilylation of Allenes [134]
R 1
I
+ Bu3Sn SiMe3 +
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858 Science of Synthesis 4.4 Silicon Compounds
R 2
R 3
Pd(dba)2
toluene
R1 = H; R2 = R3 = Me 85%
R1 = 2-OMe; R2 = R3 = Me 83%
R1 = 4-Ac; R2 = H; R3 = Cy 80%; (E/Z) 92:8
Allylsilanes 65; General Procedure: [134]
A 50-mL flask containing Pd(dba) 2 (0.0287 g, 0.05 mmol) was purged with N 2 (3 ”). Toluene
(3 mL), the organic halide (1.00 mmol), the allene (2.00 mmol), and Bu 3SnSiMe 3 (360 mg,
1 mmol) were then added bysyringe to the flask. The mixture was heated with stirring
at 808C for 7 h. The soln changed color rapidlyfrom purple-red to pale yellow in the first
few min and maintained the same color for the rest of the reaction. As the reaction approached
completion, a black precipitate of Pd(0) appeared graduallyon the wall of the
flask. At the end of the reaction, the soln was filtered through Celite. The filtrate was concentrated,
and the residue was purified bycolumn chromatography(silica gel, hexane).
Trimethyl(3-methyl-2-phenylbut-2-enyl)silane (65, R 1 =H;R 2 =R 3 = Me); yield: 85%.
[2-(2-Methoxyphenyl)-3-methylbut-2-enyl]trimethylsilane (65, R 1 = 2-OMe; R 2 =R 3 =
Me); yield: 83%.
4.4.40.18 Method 18:
From Lithium Allyl Alcoholates and Hexamethyldisilane
A direct synthesis of terminally substituted allylsilanes from allyl alcohols involves the
generation of lithium allyl alcoholates with methyllithium and follow-up treatment
with hexamethyldisilane in hexamethylphosphoric triamide. For example, both allyl alcohols
66 and 67 give mixtures of the E- and Z-allylsilanes 11, in which the E-isomer predominates
(Scheme 31). [135] Apart from allyl alcohols, carbonyl compounds can also be
used as precursors to lithium allyl alcoholates; the latter are generated in situ by 1,2-addition
of vinyllithium to saturated carbonyl compounds, or by addition of alkyllithium to
á,â-unsaturated carbonyl compounds. This one-pot reaction occurs presumably by counterattack
of the trimethylsilyl anion, generated by the reaction of alkoxide and hexamethyldisilane,
on the silyl ether intermediate. This method does not work for the preparation
of cyclic allylsilanes from cyclic allyl alcohols, such as cyclohex-2-en-1-ol.
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
R 2
R 3
65
R 1
SiMe3