The previously unknown 3H-1, 2-pyrido-(3a, b) and 3H-1, 2-thieno-(3c, d) diazepines were prepared from the corresponding 1H-isomers. Treatment of 3 with bases or acids resulted in tautomerization to give the 1H-diazepines (1), and photolysis of 3 afforded the condensed 3-vinylpyrazoles (4). However, thermolysis of the pyridodiazepines (3a, b) gave 4a, b, whereas the thienodiazepines (3c, d) gave the thienylpyrazoles (5) on irradiation via a [1, 5] hydrogen shift in the diazepine ring ; this mechanism was confirmed by a deuterium-labelling experiment. The 3-acetoxy-(13a) and 3-methoxy-(13b) 3H-1, 2-thienodiazepines were also prepared, and their photolysis afforded 3-vinylpyrazoles (14). However, thermolysis or base treatment of 13 resulted in loss of nitrogen to give compounds (15) and (16).