Organocatalytic Enantioselective aza-Henry reaction of Pyrazolone Ketimines

Abstract

An efficient and enantioselective aza-Henry reaction of pyrazolone ketimines with nitroalkanes has been realized by employing low loading of 1 mol% of a cinchona alkaloid-derived bifunctional squaramide as an organocatalyst. It is worth noting that using BrCH2NO2 observably accelerated the reaction rate and improved the yield and enantioselectivity compared with MeNO2. The addition products were obtained in high yields (up to 97%) with good to excellent enantioselectivities (up to 96% ee). This transformation provides a practical method for preparation of chiral β-nitroamines with pyrazolone skeletons.