1,2,3-and 1,2,4-triazolium salts, pyrazoles, and quinoxalines from diarylnitrilimines and isocyanides: A study of the scope

Formation of the four title compounds has been found to be strongly dependent on substituents: 1,2,3-Triazolium salts 6 do not arise from nitrilimines 2 that have an electron-acceptor attached to either the C- or the N-phenyl group. Likewise tert-butyl and aryl isocyanides do not afford this class of compounds; from the former isocyanide, dequaternization products 7 are obtained instead, whereas from the latter 1,2,4-triazolium salts 11 are formed. Compounds 11 with a tert-butyl group at the ring are unstable too, giving rise to triazoles 13. Pyrazole formation (analogues of 14) is completely suppressed when both tert-butyl and aryl isocyanides are used, whereas access to this ring system works best with sec-alkyl isocyanides (the influence of substituents of 2 being almost negligible in this case). Formation of quinoxalines 23 which arise from intermediary 1,2-diazets 22 by ring expansion is much favoured on employment of 2 that bears a donator substituent at the N-phenyl group, and under this premise ring closure to 22 is virtually independent on the nature of the isocyanide. Formation of 23 is not observed with 2 having acceptor groups.