Asymmetric Michael addition of 4H-thiopyran-4-one to nitroolefins catalyzed by diamine mono-N-sulfonamide and its application to concise synthesis of enantiopure multiring heterocycles

A new series of mono-N-sulfonamides of C2-symmetrical 2′-bipyrrolidine have been designed, synthesized, and successfully applied as the organocatalysts to the enantio- and diastereoselective Michael addition of 4H-thiopyran-4-one to a variety of nitroolefins. Catalyst 10 was identified in the examinations to exhibit more superior catalytic ability than the traditional chiral pyrrolidine catalysts, giving high chemical yields, excellent diastereo- and enantioselectivities (up to 99:1 dr and 98% ee). The tert-butyl sulfonamide functionality of catalyst 10 is speculated to play crucial roles in the transition state as both bulky group and hydrogen-bond acceptor. Application of a representative Michael adduct has been also studied and proven to be useful for the diversity-oriented synthesis of enantiopure multiring heterocycles through a unique common bicyclic nitrone intermediate.