Enantioselective Synthesis of 2-Benzothiazolyl oxiranes

Lithiation of 2-(chloroethyl)benzothiazole 1a gives (benzothiazolylchloroethyl)lithium 1b. The reaction of 1b with ketones in the presence of (-)-sparteine leads to chlorohydrins 2a-c that cyclize to epoxides 3a-c, enantioselectively, the enantiomeric enrichment being dependent upon the solvent, the lithiating agent, the reaction time. The reaction with aldehydes furnishes chlorohydrins 2d-g and then epoxides 3d-g diastereo- and enantioselectively