Cyclisation reactions involving the oxidation of carboxylic acids with lead tetra-acetate. Part III. Oxidation of phenyl- and o-biphenylyl-substituted acetic and propionic acids, and of o-biphenylylmethylmalonic acid

Abstract

The lead tetra-acetate oxidation of phenylacetic acid and o-biphenylylacetic acid gives, as major products, esters, the formation of which is suggested as proceeding via the intramolecular decomposition of intermediate lead (IV) salts. Appreciable formation of benzyl-type radicals in these reactions appears unlikely, since products unambiguously derived from such radicals are found in low yield. 3-Phenylpropionic acid and 3-(o-biphenylyl)-propionic acid give rise to the corresponding phenethyl and o-biphenylylethyl radicals. The former substitute in the solvent benzene, whereas the latter undergoes an intramolecular cyclisation to form 9,10-dihydrophenanthrene. Oxidation of o-biphenylylmethylmalonic acid gives a good yield of phenanthrene, the formation of which via 9,10-dihydrophenanthrene-9-carboxylic acid is tentatively proposed.