Enantioselective Organocatalytic Transfer Hydrogenation of 1,2-Dihydroquinoline through Formation of Aza-o-xylylene

A new way of forming the aza-o-xylylene with easily accessible 1,2-dihydroquinolines as precursor has been developed. The presence of an electron-donating group at the proper position of 1,2-clihydroquinoline was crucial for protonation of the alkene through dearomatization with a simple Bremsted acid. The in situ forming reactive intermediate was trapped with Hantzsch ester to afford tetrahydroquinolines in excellent yield and enantioselectivity.