Stereocontrol using a heterosubstituted allylic carbanion. Regio- and stereo-selective reactions of trimethylsilyl allylic carbanions with aldehydes

Regio- and stereo-selective coupling between trimethylsilyl allyl carbanions and aldehydes is achieved in the presence of an additive, ‘M’; use of R2BCl or EtAlCl2 as the additive gives the threo isomer (3) predominantly, while use of Bu3SnCl–BF3 affords the erythro isomer exclusively.