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

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 OO lysis in the Criegee intermediate. In addition, oxygen-18 labelling experiment revealed that a homolytic OO lysis in the Criegee intermediate yields muconic anhydride. These results suggest that the cleavage fashion of the OO 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.

Graphical abstractWe examined the factors that determine the regioselectivity of the oxygenation reaction of 1,2-quinone by peroxybenzoic acids in order to provide mechanistic insights into the regioselective cleavage of catechols catalysed by the enzymes. The results suggest that the cleavage fashion of the OO bond in the Criegee intermediate determines the regioselectivity of the oxygen atom insertion into 1,2-quinones. Figure optionsDownload full-size imageDownload as PowerPoint slide