Enantio­selective, Lewis Base-Catalyzed Carbosulfenylation of Alkenyl­boronates by 1,2-Boronate Migration

A catalytic, enantio­selective method for the preparation of chiral, non-racemic, alkyl­boronic esters bearing two vicinal stereo­genic centers is described. The reaction proceeds via a 1,2-migration of a zwitter­ionic thiiranium–boronate complex to give exclusively anti carbo­sulfenyl­ation products. A broad scope of aryl groups migrate with good yield and excellent enantio­selectivity (up to 99:1 e.r.). Similarly, a range of di- and trisubstituted alkenyl­boronic esters are competent reaction partners. This method provides access to both secondary and tertiary chiral alkyl­boronic esters.