Page 834 - Advanced Organic Chemistry Part B - Reactions & Synthesis

810 CH 2 COC H + (CH ) SiCl CH 2 COC H
3 3
2 5
2 5
Li Si(CH )
CHAPTER 9 3 3 Ref. 67
Carbon-Carbon
Bond-Forming Reactions
of Compounds of Boron, Metallation of alkenes with n-BuLi-KOC CH provides a route that is stereoselective
3 3
Silicon, and Tin for Z-allylic silanes. 68 (See p. 632 for discussion of this metallation method.)
R
n-BuLi R K
)
RCH CH CH 2 (CH ) SiCl Si(CH 3 3
3 3
2
)
KOC(CH 3 3
50 – 75% yield
R = alkyl Z:E = 95 – 98:5 – 2
These conditions are also applicable to functionalized systems that are compatible with
metallation by this “superbase.” 69
HO CH 3 1) n-BuLi HO CH 3
KOC(CH )
3 3
CH 3 CH 3 2) (CH ) SiCl CH 3 CH Si(CH ) 38%
2
3 3
3 3
Silicon substituents can be introduced into alkenes and alkynes by hydrosilation. 70
This reaction, in contrast to hydroboration, does not occur spontaneously, but it can be
carried out in the presence of catalysts such as H PtCl , hexachloroplatinic acid. Other
6
2
catalysts are also available. 71 Halosilanes are more reactive than trialkylsilanes. 72
Cl
CH SiCl H
2
3
CH 2 CH 2 SiCH 3
H 2 PtCl 6
Cl
Alkenylsilanes can be made by Lewis acid–catalyzed hydrosilation of alkynes.
73
Both AlCl and C H AlCl are effective catalysts. The reaction proceeds by net anti
3 2 5 2
addition, giving the Z-alkenylsilane. The reaction is regioselective for silylation of the
terminal carbon.
PhCH Si(C H )
AlCl 3 2 2 5 3
PhCH C CH + (C H ) SiH
2
2 5 3
H H

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68
O. Desponds, L. Franzini, and M. Schlosser, Synthesis, 150 (1997).
69
E. Moret, L. Franzini, and M. Schlosser, Chem. Ber., 130, 335 (1997).
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71
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73
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