Construction of chiral N , O -hemiaminals via a copper-catalyzed enantioselective Michael/ N -hemiacetalization cascade reaction.

An efficient Michael/ N -hemiacetalization cascade reaction of 5-aminoisoxazoles with β,γ-unsaturated α-ketoesters was developed under the catalysis of a chiral copper complex. A series of optically pure six-membered ring N , O -hemiaminals were obtained with excellent yields (up to 96% yield) and high enantioselectivities (up to 98% ee). The possible transition state was supported by DFT calculations and thereby the corresponding mechanism was proposed.