Photorearrangement oxadiazoles

An interesting synthesis of targeted 5-perfluoroalkyl-l,2,4-triazoles takes advantage of the aforementioned MNAC [70] photorearrangement of 3-methylamino-l,2,4-oxadiazoles 109 (R = Me) which, when irradiated at 313 nm in methanol and in the presence of various nitrogen nucleophiles (ZH in Scheme 12.32), produces triazoles 119 together with the 1,3,4-oxadiazoles 112 expected from the base-catalyzed RCRE route (Scheme 12.32) [71]. 

Pace, A., Buscemi, S. and Vivona, N. (2005) Heterocyclic rearrangements in constrained media. A Zeolite-directed photorearrangement of 1,2,4-oxadiazoles. Journal of Organic Chemistry, 70 (6), 2322-2324. 

Although simple derivatives such as the 2-amino-5-trifluoromethyl-l,3,4-oxadiazole 87 (Rp=CF3) can be prepared by reaction of trifluoroacetylhydrazine with BrCN, an interesting alternative is represented by the photorearrangement of the corresponding 1,2,4-oxadiazoles [26,45],... 

Very recent unpublished studies from our laboratories showed also the possibility to exploit the intrazeolite photorearrangement of 1,2,4-oxadiazoles [45] for the preparation of fluorinated diaryl-l,3,4-oxadiazole derivatives 90 (Scheme 27). 

Buscemi, S., Cicero, M. Vivona, N., and Caronna, X, Heterocyclic photorearrangements. Photochemical behavior of some 3,5-disubstituted 1,2,4-oxadiazoles in methanol at 254 nm, /. Heterocyclic Chem., 25, 931, 1988. 

Buscemi, S., Macaluso, G., and Vivona, N., Heterocyclic photorearrangements — photochemical behavior of some 3-acetylamino-5-aryl-l,2,4-oxadiazoles. A photoinduced iso-heterocydic rearrangement, Heterocycles, 29,1301, 1989. 

Buscemi, S., Cusmano, G., and Gruttadauria, M., Heterocyclic photorearrangements. Photoinduced rearrangement of 3-styryl-l-2,4-oxadiazoles,/. Heterocyclic Chem., 27, 861,1990. 

---