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Herstellung der 1 H ‐Indazole durch Photolyse von 2‐Aminophenylketon‐ O ‐(äthoxycarbonyl)oximen und von 3,1,4‐Benzoxadiazepin‐2 (1 H )‐onen
Author(s) -
Pfoertner KarlHeinz,
Foricher Joseph
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650317
Subject(s) - chemistry , indazole , photodissociation , radical , isomerization , intramolecular force , medicinal chemistry , photochemistry , solvent , molecule , stereochemistry , organic chemistry , catalysis
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.