Persulphate oxidations. Part VI. Oxidation of biphenyl-2-carboxamides

Persulphate oxidation of a series of N- and ring-substituted biphenyl-2-carboxamides gave the corresponding phenanthridones in yields ranging from 2 to 97%. Usually the phenanthridone was accompanied by small quantities of the appropriate dibenzo[b,d]pyran-6-one, both products arising via the same amidyl radical, which can cyclise on nitrogen or on oxygen. Oxidation of 2′-substituted biphenyl-2-carboxamides usually led to the elimination of the 2′-substituent and preferential cyclisation on oxygen; similar treatment of 2-acylaminobiphenyls gave low yields of N-acylcarbazoles.