The Rhodium Complex-catalyzed Synthesis of Quinolines from Aminoarenes and Aliphatic Aldehydes

A variety of aminoarenes react with aliphatic aldehydes in the presence of a catalytic amount of a rhodium complex and an excess amount of the corresponding nitroarenes at 180 °C to give 2-alkyl- and 2,3-dialkyl-substituted quinolines in excellent yields. Among the rhodium complexes examined, [Rh(norbornadiene)Cl]2 exhibits the highest activity as a catalyst. Thus, 2-methyl-, 2-ethyl-3-methyl-, 2-propyl-3-ethyl-, and 2-butyl-3-propylquinoline derivatives are readily obtained from aminoarenes and ethanal, propanal, butanal, and pent-anal respectively.