Ruthenium(II)-Catalyzed Transfer Hydrogenation of Aromatic and Heteroaromatic Aldehydes in Air

Abstract

Aromatic and heteroaromatic aldehydes are efficiently reduced to their corresponding alcohols in the presence of [RuCl2(p-cymene)]2 and KOAc in 2-propanol under air at 80 °C. The presence of KOAc in the reaction is essential; in its absence no reduction takes place. A highly efficient, external-base-free reduction of aldehydes has also been reported with (η6-arene)ruthenium(II) complexes containing O^O chelate ligand such as [Ru(OAc)2(p-cymene)] and [RuCl(KA)(p-cymene)], obtaining alcohol in excellent yield (OAc, acetate; KA, kojic acetate). The scope of the reaction has been extended to a broad range of aromatic and heteroaromatic aldehydes.