Enantioselective N-Heterocyclic Carbene Catalysis that Exploits Imine Umpolung

The catalytic umpolung of imines remains an underdeveloped approach to reaction discovery. Herein we report an enantioselective aza-Stetter reaction that proceeds via imine umpolung using N-heterocyclic carbene catalysis. The reaction proceeds with high levels of enantioselectivity (all >= 96:4 er) and good generality (21 examples). Mechanistic studies are reported and are consistent with turnover-limiting addition of the NHC to the imine.