Catalytic asymmetric three-component 1,3-dipolar cycloaddition of aldehydes, hydrazides, and alkynes.

Catalytic asymmetric 1,3-dipolar cycloadditions offer expeditious ways to afford synthetically important chiral heterocycles. Although a variety of 1,3-dipoles can be employed in this context, the use of acyclic azomethine imines as a facile means to give chiral pyrazolines and pyrazolidines remains completely unexplored. We report herein the first catalytic asymmetric 1,3-dipolar cycloaddition of terminal alkynes with acyclic azomethine imines generated in situ from the corresponding aldehydes and hydrazides, which was realized using Cu(I)/pybox and axially chiral dicarboxylic acid cocatalysts.