Secondary-secondary diamine catalysts for the enantioselective Michael addition of cyclic ketones to nitroalkenes

Secondary-secondary diamines derived from S-proline are efficient catalysts for the ketone-nitroalkene Michael addition reaction. The stereoselectivity of the Michael addition is dependant on the pK_a of the N-substituted aminomethyl pendant in these diamines. N′-Aryl aminomethyl pyrrolidines provide γ-nitroketones with moderate to good enantiomeric excess (65-92%). Removal of the hydrogen-bond donor group by N-methylation results in a dramatic reduction of enantioselectivity (average ee 6%).