Pyrrolidine-pyridinium based organocatalysts for highly enantioselective Michael addition of cyclohexanone to nitroalkenes

A novel class of pyrrolidine-pyridinium based organocatalysts has been developed and demonstrated to efficiently catalyze the asymmetric Michael addition reactions of unmodified cyclohexanone to nitroalkenes in the ionic liquid BMImBF4 with up to 95% yield and nearly 100% ee. The catalytic system could be reused for four times and still retained high enantioselectivity. X-ray crystallographic analysis results suggested that a sterically hindered pyridinium moiety on the catalyst played an important role in the chiral induction.