Highly Enantioselective Ruthenium-Catalyzed Cascade Double Reduction Strategy: Construction of Structurally Diverse Julolidines and Their Analogues

Abstract

A direct and facile construction of optically pure julolidine derivatives through ruthenium-catalyzed enantioselective cascade hydrogenation and reductive amination of 2-(quinolin-8-yl)ethyl ketones has been developed. By means of this protocol, various chiral julolidine compounds were obtained in high isolated yields (up to 94%) with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to 99% ee) under mild conditions. Furthermore, the synthetic practicality of this protocol was illustrated by the preparation of hexahydrojulolidines and a chiral fluorescent molecular rotor.