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

• Published in: Journal of heterocyclic chemistry 2003-07, Vol.40 (4), p.625-637
• Main Authors: Moderhack, Dietrich, Daoud, Ali
• Format: Article
• Language: English
• ISSN: 0022-152X; 1943-5193
• DOI: 10.1002/jhet.5570400411

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 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 see‐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.