Catalytic Asymmetric Thioacetalization of Aldehydes

A catalytic enantioselective thioacetalization reaction has been developed. Various aldehydes react with unsymmetrical 1,3- or 1,2-dithiols to furnish chiral, enantioenriched thioacetals in excellent enantioselectivities upon treatment with a nitrated imidodiphosphoric acid catalyst. The transformation is assumed to proceed via a thionium ion intermediate.