Quinoxaline-specific enantioselective sulfa-michael reaction catalyzed by chiral phosphoric acid

Highly enantioselective sulfa-Michael additions(SMA) between 2-alkenyl quinoxalines and aromatic thiols are accomplished using a low loading of chiral phosphoric acid catalyst(1 mol%). It was confirmed by an investigation of a lot of azaarenes that the two C=N units of quinoxalines are indispensable for controlling the reaction enantioselectivities. A series of non-terminal 2-alkenes substituted with aryls or alkyls, even other electro-withdrawing groups such as ketones, esters, or amides, selectively reacted and afforded the desired SMA products(48 examples) in good regioselectivities with high yields(up to 99%) and good ee values(up to 97%).