1.2.4- Oxadiazoles Photochemistry

The photochemistry of 3-amino- <2002JOC6253> and some 3-iV-alkylamino-5-perfluoroalkyl-l,2,4-oxadiazoles <2004JOC4108> was investigated. The latter reaction led to 5-perfluoroalkyl-l,3,4-oxadiazoles followed eventually by their conversion into 5-perfluoroalkyl-l,2,4-triazoles. 1,3,4-Oxadiazoles were also obtained by photochemical interconversion of 3-acylamino-l,2,5-oxadiazole derivatives. Mechanisms of these reactions were proposed <2004JOC4108>. Examples of these interconversions are shown in Scheme 37. 

Buscemi, S., Vivona, N. and Caronna, T. (1996) Photoinduced molecular rearrangements. The photochemistry of some 1,2,4-oxadiazoles in the presence of nitrogen nucleophiles. Formation of 1,2,4-triazoles, indazoles, and benzimidazoles. Journal of Organic Chemistry, 61 (24), 8397-8401. 

Little interest has been shown this year in the photochemistry of five-membered heteroaromatic compounds. A theoretical study of the photoisomerization of 2-cyanopyrrole to 3-cyanopyrrole has been described.The formation of 2-acetyl-aminoquinazolin-4-ones on irradiation of 3-acetylamino-5-aryl-1,2,4-oxadiazoles (45) in methanol is thought to involve initial rearrangement to the corresponding 3-aroylamino-5-methyl-l,2,4-... 

This chapter deals with the photoisomerization reactions of pyrazoles, 1,2,4-oxadiazoles, pyridine, and its simple derivatives and pyridinium cations. The photochemistry of nitrogen-containing heteroaromatic compounds that also contain sulfur are considered in another chapter. 

The photochemistry of 3-benzoylamino-5-methyl-l,2,4-oxadizole 98 and 3-acetylamino-5-phenyl-1,2,4-oxadiazole 99 has also been investigated (Scheme 26). 

Newman, H., Photochemistry of 3,5-diphenyl-1,2,4-oxadiazole, I. Photolysis in aprotic media. Tetrahedron Lett., 2417, 1968. 

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