Photolysis and thermolysis of highly substituted 1H-1,2-diazepines

Photolysis of the methyldiazepine (5a) led directly to the pyrazole (7) whereas the ethoxycarbonyl- and acetyl-diazepines (5b) and (5c) gave cycloadducts (6b) and (6c); thermolysis of the diazepines (5) or the diaza[3,2,0]bicycloheptadienes (6) produced mainly ylides (8) and small amounts of 2,4,6-triphenylpyridine (9), except for (5a) which yielded (9) only.