Enantioselective Aza-Henry Reaction of Imines Bearing a Benzothiazole Moiety Catalyzed by a Cinchona-Based Squaramide

An efficient enantioselective aza-Henry reaction of nitroalkanes to imines bearing a benzothiazole moiety catalyzed by a Cinchona-based squaramide has been developed. In the reaction of imines, the corresponding products were obtained in good to excellent yields (up to 99%) with excellent enantioselectivities (up to >99% ee) for most of the aromatic substituted imines. The imines with electron-withdrawing groups gave better yields than those bearing electron-donating groups in the aza-Henry reaction. Moreover, a one-pot three-component enantioselective aza-Henry reaction using 2-aminobenzothiazoles, aldehydes, and nitromethane was also developed. Moderate to good yields and high enantioselectivities were obtained in the one-pot cases (up to 98% ee).