Reactions of Carbonyl Compounds with a-Trimethylsilylcarbanions

In general, the elimination reactions are anti under acidic conditions and syn under basic conditions. This stereoselectivity is the result of a cyclic elimination mechanism under basic conditions, whereas under acidic conditions an acyclic //-elimination occurs. 

3C Me3SiCHCN + 06II5On=CHCHO — C6H5CH=CHCH=CHCN 95% Li 

5e Me3SiCHSC6H5 + C6H5CH=CHCHO — C6H5CH=CHCN=CHSC6H5 70% Li 

The anti elimination can also be achieved by converting the jS-silyl alcohols to trifluoro- 

3 MesSiCHCN + C6H5CH=CHCHO — C6H5CH=CHCH=CHCN 95% 

5 Me3SiCHSC6H5 + CgHsCB CHCHO — C6H5CH=CHCN=CHSC6H5 70% 

Sulfur ylides are next to phosphorus ylides in importance as synthetic reagents. Dimethylsulfonium methylide and dimethylsulfoxonium methylide are especially useful. These sulfur ylides are prepared by deprotonation of the corresponding sulfonium salts, both of which are commercially available. 

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