Studies on palladium-catalyzed enantioselective cyclization of 3,4-allenylic hydrazines with organic halides

A convenient route to optically active pyrazolidine derivatives from Pd(0)/(R,R)-Bn-BOX-catalyzed enantioselective cyclization of 3,4-allenylic hydrazines in the presence of organic halides has been developed, the ee value is 75–84%. The absolute configuration of the products was determined by the conversion of one of the products to a known product prepared in this group. The reaction may proceed via the oxidative addition, intermolecular carbometallation of the allene moiety forming a π-allylic palladium intermediate, and the intramolecular enantioselective allylation.