ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19760590512
