Metalloporphyrin-catalyzed oxidation of 2-cycloalkyl-3-hydroxynaphthoquinones

Mild H2O2 oxidation of a small series of 2-cycloalkyl-3-hydroxynaphthoquinones catalyzed by 5,-10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphineiron(III) chloride in methanol-dichloromethane leads in each case to the isolation of a dehydro-dimer identified as a 3-cycloalkyl-3-(2-cycloalkylnaphthoquinon-3-yl)oxy-2-oxo-2,3-dihydronaphtho-1,4-quinone and in some cases to a 2-cycloalkyl-2,3-dihydroxy-1-oxoindan-3-carboxylate. The mechanism of formation of the former is rationalized in terms of nucleophilic attack of unreacted hydroxynaphthoquinone anion upon an epoxide primary oxidation product, while that of the latter is proposed to involve nucleophilic attack of solvent methanal on the same epoxide followed by rearrangement.