Studies on diazepines. VIII. Syntheses and rearrangements of 3H-1,2-pyrido- and 3H-1,2-thieno-diazepines

Article abstract of DOI:10.1248/cpb.27.2188

The previously unknown 3H-1,2-pyrido- and 3H-1,2-thieno- diazepines (3a:3H-1,2 pyrido [2,3-c] diazepine; 3b:3H-1,2 pyrido [3,2-c] diazepine; 3c:3H-1,2 thieno [2,3-c] diazepine; 3d:3H-1,2 thieno [3,2-c] diazepine) were prepared from the corresponding 1H-isomers. Treatment of 3 (the parent 3H-diazepine) with bases or acids resulted in tautomerization to give the 1H-diazepines 1 (the parent 1H-1,2 diazepine), and photolysis of 3 afforded the condensed 3-vinylpyrazoles 4 (the parent 3-vinylpyrazole). However, thermolysis of the pyridodiazepines (3a,3b) gave 4a(3-vinyl-1H-pyrido[2,3-c]pyrazole), 4b(3-vinyl-1H-pyrido[3,2-c]pyrazole), whereas the thieno-diazepines (3c,3d) gave the corresponding 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 corresponding 3-vinylpyrazoles (14). However, thermolysis or base treatment of 13 resulted in loss of nitrogen to give the corresponding cyclopentenothiophene (15) and acetal (16).

Full text of DOI:10.1248/cpb.27.2188

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