Cyclisation reactions involving the oxidation of carboxylic acids with lead tetra-acetate. Part II. The conversion of 5-arylvaleric acids into 1,2,3,4-tetrahydronaphthalenes

Abstract

The lead tetra-acetate oxidation, in benzene solution under a nitrogen atmosphere, of 5-phenylvaleric acid, 5-(p-nitrophenyl)valeric acid, 5-(β-naphthyl)valeric acid, and 5-(p-methoxyphenyl)-5-phenylvaleric acid affords as products 1,2,3,4-tetrahydronaphthalene, 6-nitro-1,2,3,4-tetrahydronaphthalene, 1,2,3,4-tetrahydroanthracene, and 1,2,3,4-tetrahydrophenanthrene, 1-(p-methoxyphenyl)-1,2,3,4-tetrahydronaphthalene, and 6-methoxy-1-phenyl-1,2,3,4-tetrahydronaphthalene respectively. The formation of these products is readily explained by the intramolecular cyclisation of free-radical intermediates produced on oxidative decarboxylation of the acids. In the oxidation of 5-phenylvaleric acid in cyclohexane an additional major product is 2-octyl 5-phenylvalerate, the formation of which may involve ring opening of cyclohexane.