Mechanistic study on regioselective oxygenation reaction of 1,2-quinones with peroxybenzoic acids: Relevant to mechanisms of catecholdioxygenases

Abstract

The reaction of 1,2-quinone with peroxybenzoic acid affords two types of oxygenated products, muconic anhydride and 7-membered α-ketolactone, via a Criegee intermediate analogous to the proximal peroxy intermediate proposed for catecholdioxygenases. We examined factors that determine the regioselectivity of the oxygenation reaction of 1,2-quinone in order to provide mechanistic insights into the regioselective cleavage of catechols catalysed by the enzymes. Polar solvents, acid catalysts and electron-withdrawing groups on peroxybenzoic acids were found to enhance the selectivity for the formation of 7-membered α-ketolactone. These data indicate that 7-membered α-ketolactone is formed via a heterolytic O O lysis in the Criegee intermediate. In addition, oxygen-18 labelling experiment revealed that a homolytic O O lysis in the Criegee intermediate yields muconic anhydride. These results suggest that the cleavage fashion of the O O bond in the Criegee intermediate determines the regioselectivity of the reaction of not only 1,2-quinones with peroxybenzoic acids, but also the catecholate ligand with molecular oxygen in the enzymatic intermediate.