Mechanistic Studies on the Catalytic Asymmetric Mannich-Type Reaction with Dihydroisoquinolines and Development of Oxidative Mannich-Type Reactions Starting from Tetrahydroisoquinolines

TLDR: Detailed mechanistic studies on recently reported asymmetric addition reactions of malonates to dihydroisoquinolines (DHIQs) catalyzed by chiral Pd(II) complexes were carried out, allowing the efficient synthesis of optically active tetrahydrobenzo[a]quinolizidine derivatives via intramolecular Michael reaction.

Abstract: Detailed mechanistic studies on our recently reported asymmetric addition reactions of malonates to dihydroisoquinolines (DHIQs) catalyzed by chiral Pd(II) complexes were carried out. It was found that an N,O-acetal was generated in situ by the reaction of DHIQ with (Boc)2O, and cooperative action of the Pd(II) complex as an acid−base catalyst allowed the formation of a chiral Pd enolate and a reactive iminium ion via α-fragmentation. The iminium ion was also accessible via oxidation with DDQ as an oxidant, and a catalytic asymmetric oxidative Mannich-type reaction was achieved with tetrahydroisoquinolines (THIQs) as starting materials. This oxidation protocol was applicable to N-acryloyl-protected THIQs, allowing the efficient synthesis of optically active tetrahydrobenzo[a]quinolizidine derivatives via intramolecular Michael reaction.