Thiourea as an efficient organocatalyst for the transfer hydrogenation of 2-substituted quinoline derivatives

This study reports on the first transfer hydrogenation of 2-substituted quinolines promoted by a thiourea catalyst with Hantzsch ester as the hydrogen source. A wide range of quinoline derivatives, including 2-alkylquinolines and 2-arylquinolines, were efficiently reduced to give 1,2,3,4-tetrahydroquinolines with good to excellent yields. The operational simplicities and conveniences of this reaction pathway render this protocol considerably promising in the preparation of biologically active tetrahydroquinoline derivatives.