OXIDATION OF DIETHYL 3-PHENYLPROPYLMALONATE - A MECHANISTIC PROBE FORALTERNATIVE BENZYLIC AND ALPHA-CARBONYLALKYL C-H ACTIVATION

Oxidation of diethyl 3-phenylpropylmalonate, 1, by metal salts [Mn(III ), Ce(IV), Fe(III), Co(III), Pb(IV)] and nickel peroxide affords the s ubstitution products at the malonic C-H bond (compounds 2 and/or 3) wi th high selectivity. Peroxides, positive halogen oxidants, and oxygen [under catalysis by Mn(III)] oxidize 1 at the benzylic position. The k inetics of the oxidation of 1 by Mn(III) acetate, Ce(IV) ammonium nitr ate and Fe(III) perchlorate have been investigated under conditions of selective formation of 2 and the activation parameters were deduced. The influence of NaOAc in acetic acid and CF3COOH in acetonitrile on t he kinetics of the oxidation of 1 by Mn(III) acetate was also studied. The different selectivity observed is attributed to a different mecha nism of C-H bond activation: oxidative deprotonation at the carbonyl g roup with metals and hydrogen abstraction with electrophilic radicals. The mechanism of the oxidation at the malonic group is discussed.