Cyclisation reactions involving the oxidation of carboxylic acids with lead tetra-acetate. Part I. The conversion of 2′-substituted biphenyl-2-carboxylic acids into 3,4-benzocoumarin

Abstract

The reaction of 2′-substituted biphenyl-2-carboxylic acids (where the 2′-substituent is H, CO2H, NO2, Cl, OMe, or CO2Me) with lead tetra-acetate in refluxing benzene solution, under a nitrogen atmosphere, affords 3,4-benzocoumarin as a major organic product. Only a trace is formed when the 2′-substituent is Me. o-Terphenyl-2-carboxylic acid gives no 3,4-benzocoumarin, but triphenylene is formed in good yield. It is suggested that these cyclizations involve the intermediacy of free radicals, Particularly AS The products of the thermal decomposition, in benzene solution, of the diacyl peroxides derived from 2′-substituted biphenyl-2-carboxylic acids, are similar to the products formed on reaction of the acids with lead tetra-acetate.