Photochemical Reactions Of 1h-2,3-Benzodiazepines - Valence Isomerization Of A 1,2-Diazabutadiene To A Diazetine

1H-2,3-Benzodiazepines (1) rapidly undergo photoisomerisation to 2a,7-dihydro[1,2]diazeto[4,1-a]isoindoles (7), in contrast to their carbocyclic analogues (benzocycloheptenes), which react predominantly by [1,7] hydrogen migration and ring contraction. The photoproducts (7) decompose thermally either by extrusion of YCN (where Y is the 2-substituent) or via reversion to their benzodiazepine precursors, which subsequently eliminate nitrogen or rearrange.