A highly enantioenriched, configurationally stable alpha-thioallyllithium compound and the stereochemical course of its electrophilic alkylation

[GRAPHICS] The first highly enantioenriched, configurationally stable alpha-thioallyll ithium compound (9) was generated by deprotonation of the S-cyclohex-2-enyl thiocarbamate 8. The methylation of 9 in both the alpha- and gamma-positio ns proceeds antarafacially with a high degree of chirality transmission, as was elucidated by X-ray analysis of thiocarbamates 10 and 11. The opticall y active S-allyl thiocarbamate 8 was prepared by enantiospecific [3,3]sigma tropic rearrangement of the corresponding O-allyl thiocarbamate 7.