IRON PORPHYRIN-CATALYZED OXIDATION OF 1,2-DIMETHOXYARENES - A DISCUSSION OF THE DIFFERENT REACTIONS INVOLVED AND THE COMPETITION BETWEEN THE FORMATION OF METHOXYQUINONES OR MUCONIC DIMETHYL ESTERS

This paper describes the oxidation of an alpha,beta-diarylpropane lign in dimer model and other dimethoxyarenes by several iron porphyrin-bas ed biomimetic systems. From l-(3,4-dimethoxyphenyl)-2-phenylpropanol ( 1), three types of products are identified: the 3,4-dimethoxybenzaldeh yde derived from the C(alpha)-C(beta) cleavage of the propyl side chai n and either quinones or muconic dimethyl esters resulting from oxidat ions at the level of the dimethoxyaryl group. The selectivity of the r eaction is discussed with respect to the nature and reactivity of the high-valent iron-oxo species formed upon reaction of the oxidants, H2O 2 or magnesium monoperoxyphthalate (MMP), with the iron porphyrins. Fe (TF5PP)CI-catalyzed oxidation of 1 by H2O2 in an aprotic medium (CH3CN /CH2Cl2), yields a clean ''lignin peroxidase-like'' reaction with sele ctive formation of the aldehyde. In an aqueous buffered solution, MMP oxidation of para-substituted 1,2-dimethoxyarenes catalyzed by an iron s(pentafluorophenyl)-beta-tetrasulfonatoporphyrin, Fe(TF5PS4P), clear ly depends on the electronic properties of the para-substituent. The r eaction is selective for para-quinone formation in the case of an elec tron-releasing group and for muconic dimethyl ester formation in the c ase of an electron-withdrawing group.