Electrochemical reduction of O-acylated aldehyde cyanohydrins

Abstract

Cyanohydrins of aromatic aldehydes, acylated at the hydroxyl group, are reducible in aprotic medium; the base generated during the reduction induces a rearrangement of the compound to a vicinal diketone. Thus, O-benzoyl benzaldehyde cyanohydrin ( 1) is rearranged during the reduction to benzil and O-acetyl benzaldehyde cyanohydrin to 1-phenylpropane-1,2-dione; on the cyclic voltammetric curves of the acylated cyanohydrins the radical anion of the diketone gives an anodic peak on the reverse sweep and the diketone a cathodic peak on the second negative sweep. The reduction of the diketones occurs at a higher potential than that of the O-acyl benzaldehyde cyanohydrin and the diketone is therefore reduced further at the potential used for the reduction of the acylated benzaldehyde cyanohydrin. Thus both benzil and O-benzoyl benzaldehyde cyanohydrin yield on reduction the same main product, benzyl phenyl ketone; besides that, 1 gives minor amounts of benzylcyanide and benzoic acid. Possible reaction routes are discussed.