1,2,4-Oxadiazol-5-ones, photolysis

Substituted benzimidazoles have been reported to be readily obtained by photolysis of l,2,4-oxadiazol-5-ones. Thus, irradiation of dioxane solutions of 3,4-diphenyl-l,2,4-oxadiazol-.5-one (CCXLVII ) and of 3-carbalkoxy-2-phenyl-l, 2,4-oxadiazol-5-one (CCXLIX) with ultraviolet light yielded 2-phenyl- (CCLa),5 and 2-carbalkoxybenzimidazoles (CCLb), 6 respectively. 

Complex products were also obtained from electron-poor dienes50. Photolysis of (t-Bu2Si)3 with tetrazine 8 gave a complex mixture of products, from which 9 and 10 could be isolated (equation 20). In 10, one of the CF3 groups has been completely degraded, with simultaneous rearrangement of the ring skeleton. The reaction with oxadiazole 11 also took an unexpected course (equation 21). 

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