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Oxidation and acid‐catalyzed cyclization of aldehyde 2‐aminophenylhydrazones. Alternative syntheses for 1,2,4‐benzotriazines and benzimidazoles
Author(s) -
Cerri Riccardo,
Roido Alessandro,
Sparatore Fabio
Publication year - 1979
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570160534
Subject(s) - chemistry , aldehyde , hydrazone , benzaldehyde , catalysis , double bond , medicinal chemistry , ammonia , stereochemistry , organic chemistry
Aldehyde 2‐aminophenylhydrazones are easily oxidized by air to 3‐substituted 1,2,4‐benzotriazines. In two cases the intermediate 3,4‐dihydro‐1,2,4‐benzotriazines were isolated. In the absence of oxygen, acids catalyze the formation of 2‐substituted benzimidazoles with loss of ammonia. It is suggested that both reactions proceed via 1,2,3,4‐tetrahydro‐1,2,4‐benzotriazines (III), formed by addition of the amino group on the hydrazone double bond. Such cyclic forms (III) predominate over the open chain structures (II) in the cases of aliphatic and arylalkylaldehyde 2‐aminophenylhydrazones, as supported by nmr spectra, while benzaldehyde 2‐aminophenylhydrazone exists mainly or exclusively in the open chain form (II).