Rhodium(III)-catalyzed dimerization of aldehydes to esters.

In response to the increasing social demand for clean and environmental friendly procedures, recent years have witnessed a dramatic growth in the search for selective chemical processes with 100% atom economy. Among them, the catalyzed coupling of aldehydes to the corresponding esters (Tishchenko reaction, Scheme 1) is key for the synthesis of these valuable chemicals. 1] This reaction and the related dismutation of aldehydes known as the Cannizzaro reaction typically suffer from the formation of side products, but it represents an attractive alternative to traditional ester syntheses that require, in general, the activation of the free acid through conversion to the acyl chloride or anhydride 2 ] with the subsequent production of wastes. In this context, a new catalytic approach providing esters by dehydrogenation of alcohols has been recently reported by Milstein.