Rationally-designed S-Chiral bissulfinamides as highly enantioselective organocatalysts for reduction of ketimines

We recently reported the first example of S-chiral organocatalysts, that are highly efficient and enantioselective in substoichometric amounts, and which use a chiral monosulfinamide group as Lewis base to activate trichlorosilane (HSiCl3) to reduce N-arylketimines. A plausible mechanism involving two molecules of the monosulfinamde catalyst for the activation of HSiCl3 prompted us to design S-chiral bissulfinamides as new catalysts. We herein describe our findings that an easily prepared S-chiral bissulfinamide bearing a five-methylene linkage not only inherited the excellent substrate generality from the monosulfinamide catalysts, but also exhibited further improved enantioselectivity.