Dibenzo[d,f][1,2,3]triazepine and the attempted generation of 2,2′-didehydrobiphenyl

Abstract

Dibenzo[d,f][1,2,3]triazepine, the first reported 1,2,3-triazepine, has been prepared in high yield by addition of ammonia to bis-diazotised 2,2′-diaminobiphenyl. Various mechanisms are considered for this reaction since complexities are revealed when ammonia is replaced by methylamine.

The instability of the triazepine ring and its tendency to act as a masked diazonium compound accounts for the complexity of diazotisation of 2,2′-diaminobiphenyl which, under various conditions, gives carbazole, benzocinnoline, 2-amino-2′-azidobiphenyl, benzocinnoline N-imide, 1,3-bis-(2-aminobiphenyl-2-yl)triazene, and 9,20-dihydrotetrabenzo[d,f,k,m][1,2,3,8,9,10]hexa-azacyclotetradecine, a new heterocyclic system (Scheme 1). The dibenzotriazepine reacts as a masked diazonium compound with hydrobromic acid and copper, hydriodic acid, hydrazine, diethyl malonate, and on catalytic hydrogenation (Scheme 2).

The N(5)-methyl derivative of the triazepine is formed by methylation but attempts to introduce other N-substituents have so far been unsuccessful. In particular, failure to isolate the unstable N(5)-amino-derivative has precluded the generation of 2,2′-didehydrobiphenyl.