Metal Salt Mediated Radical Reactions of 2-Substituted-1,4-Naphthoquinones

The silver(II)- and manganese(III)-mediated radical reactions of 2-substituted-1,4-naphthoquinones are described. Acyl radicals generated by the oxidative decarboxylation of alpha-keto acids with silver(I) nitrate and persulfate undergo efficient radical addition to the C=C bond of 2-(1-hydroxyalkyl)-1,4-naphthoquinones and 2- (1-amidoalkyl)-1,4-naphthoquinones. This reaction provides an effective method for the synthesis of naphtho[2,3-c]furan-4,9-diones and benzo[f]isoindole-4,9-diones. In the presence of O-2, manganese(III) acetate oxidation of beta-keto esters also generates acyl radicals, which then undergo radical addition to 2-(1-amidoalkyl)-1,4-naphthoquinones, and subsequently, benzo[f]isoindole-4,9-diones are produced.