Facile synthesis of novel 3‐quinoxalinyl‐1,5‐benzodiazepines via ring transformation. Stable tautomers in the 1,5‐benzodiazepin‐2‐one ring system

Novel 3-quinoxalinyl-1,5-benzodiazepines 4, 5, 6, 9, 10 were synthesized via the ring transformation of 3-(N,N-dimethylcarbamoyl)furo[2,3-b]quinoxaline hydrochloride (1). The 3-quinoxalinyl-1,5-benzodiazepine hydrochlorides 4 and 6 are the tautomers of the N1′-H (or N5-H) form and the C3-H form, respectively, which are stable in solid and solution. However, 4 (NH form) was found to be converted into 6 (C3-H form) by refluxing in acetic acid. The individual spectral evidences and different reactivity of these tautomers are described.