Enantioselective Stetter reactions of enals and modified chalcones catalyzed by N-heterocyclic carbenes.

Organocatalytic activation of readily available substrates has led to the rapid development of many enantioselective reactions in the last decade. In N-heterocyclic carbene (NHC) catalysis, reactions of enals with enones or enone derivatives have been extensively investigated and are reported to undergo a diverse set of transformations based on the catalytically generated enolate and homoenolate equivalents as intermediates. In contrast, the NHC-catalyzed enantioselective Stetter-type Michael additions of enals to enones remain challenging in part due to the competing and often dominant homoenolate or enolate pathways. Herein we report an enantioselective Stetter reaction of enals and modified chalcones using triazoliumbased NHC catalysts [Eq. (1)]. The previously reported