Antitumour benzothiazoles. Part 2. Formation of 2,2′-diaminobiphenyls from the decomposition of 2-(4-azidophenyl)benzazoles in trifluoromethanesulfonic acid

Abstract

Decomposition of 2-(2-azidophenyl)- and 2-(3-azidophenyl)-benzothiazoles in trifluoromethanesulfonic acid generates π-carbocations. These reactive intermediates have been trapped by triflate anion with the nucleophile substituting para to the original azido group to yield triflate-substituted arylamines. 2-(4-Azidophenyl)-benzothiazoles and -benzoxazoles behave differently: triflate-substituted arylamines are accompanied by symmetrical or unsymmetrical benzazolyl-substituted 2,2′-diaminobiphenyls as major products. These biphenyls have been identified by their characteristic ¹H and ¹³C NMR spectra. 2,2′-Diaminobiphenyls are formed by initial C–C coupling interactions between the π-carbocations and undecomposed 2-(4-azidophenyl)benzazoles and not by benzidine-type rearrangements as originally proposed. Symmetrical 2,2′-diaminobiphenyls have been oxidized by (diacetoxyiodo)benzene to give novel benzazolyl-substituted benzo[c]cinnolines.