Enantioselective Transfer Hydrogenation of Quinoxalines and Quinoxalinones

Significance

Rueping and colleagues have shown that transfer hydrogenation catalyzed by BINOL-derived phosphoric acids of type 3 can be successfully applied to a variety of nitrogen heterocycles, including pyridines, quinolines, benzoxazines, benzthiazines, and benzoxazinones (see original publication for references). In this work, they disclose the hydrogenation of one further substrate class - quinoxalines 1 and quinoxalin­ones 2. Good to excellent yields and enantioselectivities were obtained with Hantzsch ester 4 and Brønsted acid 3 as the catalyst.