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- Title
Zum Mechanismus der photochemischen Umwandlung von 2-Alkyl-indazolen in 1-Alkyl-benzimidazole. I. Struktur und Reaktivität eines Zwischenproduktes.
- Authors
Heinzelmann, Willy; Märky, Michael; Gilgen, Paul
- Abstract
Mechanistic studies on the photoisomerization of 2-alkyl-indazoles into 1-alkyl-benzimidazoles. I. Structure and reactivity of an intermediate. 2-Alkyl-indazoles ( 1) undergo photochemical isomerization to 1-alkyl-benzimidazole via previously unknown intermediates 3 ( Scheme 1). In the present paper the structure and reactivity of these intermediates are discussed. Low-temperature irradiation (−60°) of 1 b with 300 nm light gives 3 b in quantitative yield. 3 b is transformed during warm-up to 1 b and 2 b (UV.-evidence). The formations of 1 and 2 show the same temperature dependence but their ratio is found to be temperature-independent. In contrast to the above behaviour, low-temperature irradiation with 250 nm light of 3 b yields 1 b only (no 2 b). These findings are consistent with the proposed reaction mechanism 2 c in Scheme 2. On the basis of spectroscopic properties and the described reaction pathways, it appears that the most suitable structure for intermediate 3 is a 7,8-diaza-tricyclo[4.3.0.07,9]nona-2,4,6(10)-trien ( 9). In Scheme 4 the reaction pathway for the iudazole-benzimidazole-rearrangement is summarized.
- Publication
Helvetica Chimica Acta, 1976, Vol 59, Issue 5, p1512
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.19760590512