Cyclisation of biphenyl-2-carboxamides

N-Methylbiphenyl-2-carboxamide was cyclised by treatment with lead(IV) acetate–iodine reagent to a mixture of cis- and trans-2-methyl-4′-acetoxy-3-oxoisoindoline-1-spirocyclohexa-2′,5′-dienes, which were hydrolysed to the corresponding alcohols and N-methylphenanthridone. Cyclisation of biphenyl-2-carboxamide and its N-methyl derivative by treatment with t-butyl hypochlorite–iodine reagent gave the corresponding 2-iodophenanthridones. The formation of the products is explained on the basis of cyclisation of the amido-radical at the 1′- and 2′-positions of biphenyl-2-carboxamide and, in the case of t-butyl hypochlorite–iodine reagent, subsequent iodination of the phenanthridone with ICI.