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