Herstellung der 1 H ‐Indazole durch Photolyse von 2‐Aminophenylketon‐ O ‐(äthoxycarbonyl)oximen und von 3,1,4‐Benzoxadiazepin‐2 (1 H )‐onen

1 H ‐Indazoles Obtained by Photolysis of 2‐Aminophenylketon‐ O ‐(ethoxycarbonyl)oximes and of 3, 1, 4‐Benzoxadiazepine‐2(1 H )‐ones Irradiation of ( E )‐ and ( Z )‐ O ‐(ethoxycarbonyl)oximes 1 of 2‐aminophenyl ketones in solution with UV, and/or visible light gives 1 H ‐indazole derivatives 2 in high yields ( Scheme 1 ). For this reaction the amino group must be un‐ or mono substituted. With the N , N ‐disubstituted ( E )‐ 1d ( Scheme 2 ) no 1 H ‐indazole formation is observed, because the radicals formed by its photolysis react in an unspecific manner with each other and with the solvent. From the behaviour of ( E )‐ 1d and from the lack of any E/Z ‐isomerization of 1 we conclude that the photoreaction starts with a splitting of the N, O‐bond in two separate radicals, whereas the radical pair produced by the also studied photolysis of 3,1,4‐benzoxadiazepine‐2(1 H )‐one derivatives 3 is fixed in the parent molecule, and therefore tends to recombine. This makes a prolonged irradiation necessary to convert the benzoxadiazepinones 3 into the 1 H ‐indazoles 2 . The different reaction rates of the ( E ) and ( Z )‐isomers of 1 (provided R 4 = H) are understood by means of different intramolecular H‐bridges.