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

✍ Scribed by Karl-Heinz Pfoertner; Joseph Foricher

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: German
• Weight: 563 KB
• Volume: 65
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19820650317

✦ Synopsis

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.