Asymmetric Aza-Michael Reaction Catalyzed by a Charged Brønsted Acid

Significance

Ooi and co-workers designed a variety of new cationic Brønsted acids for the activation of non-ionic Lewis bases, based on their previously introduced structural motif of P-spirocyclic tetraaminophosphonium frameworks (J. Am. Chem. Soc. 2007, 129, 12392 and Synfacts 2007, 1309; J. Am. Chem. Soc. 2008, 130, 14088 and Synfacts 2008, 1327). The authors found that the heterochiral catalyst 1˙BArF efficiently promoted the enantioselective conjugate addition of 2,4-dimethoxyaniline to aromatic and aliphatic nitroalkenes. The corresponding aza-Michael products were obtained in high yields (89%) and enantioselectivities (er up to 98.5:1.5).