CYCLIZATION OF ORTHO-SUBSTITUTED N-ARYLBENZIMIDOYL NITRENES .2. PREFERENTIAL CYCLIZATIONS AT AN ORTHO-POSITION BEARING A METHOXYCARBONYL GROUP

The 1-aryl-5-phenyltetrazoles (1), in which the 1-aryl group bears an ortho-methoxycarbonyl, nitro-, carboxamido-, or cyano-group, have been prepared and photolysed. The products are 2-phenylbenzimidazoles (2), which, it is suggested, result from two types of ring-closure of the intermediate benzimidoyl nitrenes: cyclisation at the free ortho-position, or cyclisation at the blocked ortho-position, followed by migration of the substituent from carbon to nitrogen. When the ortho-substituent is a methoxycarbonyl group, the second type of process competes effectively with the first. A minor product of the photolysis of these tetrazoles in acetonitrile is the corresponding 1-aryl-5-methyltetrazole (3) in which a mole of the solvent has been incorporated.