Ruthenium-Catalyzed Dehydrogenative β-Benzylation of 1,2,3,4-Tetrahydroquinolines with Aryl Aldehydes: Access to Functionalized Quinolines

A new benzylation protocol, enabling straightforward access to,beta-benzylated quinolines, has been demonstrated. By employing readily available [RuCl2(p-cymene)](2) as a catalyst and O-2 as a sole green oxidant, various 1,2,3,4-tetrahydroquinolines were efficiently converted in combination with aryl aldehydes into desired products in a step- and atom economic fashion together with the advantages of excellent functional group tolerance and chemoselectivity, offering an important basis for the transformation of saturated N-heterocycles into functionalized N-heteroaromatics via a dehydrogenative cross-coupling strategy. Mechanistic investigations support that the reaction undergoes a monodehydrogenation-triggered beta-benzylation mode.