MECHANISM OF COPPER-CATALYZED OXYGENATION OF KETONES

Deoxybenzoin (1) is converted by a Cu(II)-py-Et3N-MeOH-O2 (py = pyridine) system to a mixture of benzil (2), bidesyl (3) and the cleavage products PhCHO and PhCOOH. A product study comparing reactivities of 1 and 2 under identical conditions established that the conversion of 1 to 3 is effected by Cu(II) alone, that PhCHO is generated only from %1, in a reaction that requires both Cu(II) and O2, and that 2 undergoes C-C cleavage only in the presence of H2O, forming PhCOOH exclusively, in a reaction that requires Cu(II) but not O2. .alpha.-Methyldeoxybenzoin (5) undergoes an exceptionally slow but similar reaction (giving the tertiary .alpha.-ketol 6 rather than diketone 2). Mechanisms for these reactions are presented, and the significance of the results is discussed.