Organocatalytic Enantioselective Synthesis of Pyrazolidines, Pyrazolines and Pyrazolidinones

Enantiopure pyrazolidines, pyrazolines and pyrazolidinones have been accessed in a direct and efficient manner through an organocatalytic, enantioselective aza-Michael/hemiaminal formation cascade process from enals and N,N'-disubstituted hydrazides. The process takes place with high regio- and stereoselectivities and furnishes the target compounds in high overall yields by means of an operationally very simple methodology.