Fluorinated heterocyclic compounds. A photochemical synthesis of 3-amino-5-perfluoroaryl-1,2,4-oxadiazoles

A photochemical methodology for the synthesis of 3-amino- (or 3-N-substitut ed amino) 5-pentafluorophenyl-1,2,4-oxadiazoles is reported. Irradiation of 3-pentafluorobenzoylamino-4-methyl-1,2,5-oxadiazole (Furazan) at 254 nm in methanol and in the presence of ammonia, primary or secondary aliphatic am ines produces 3-amino-, 3-(N-alkylamino)-, 3-(N,N-dialkylamino)-5-pentafluo rophenyl-1,2,4-oxadiazoles. The photoreaction follows the fragmentation pat tern of the furazan ring with the extrusion of acetonitrile and the formati on of a counterpart fragment which the nitrogen nucleophile will capture. D epending on the nature of the reagent, displacement of a fluoride anion at the C(S)-pentafluorophenyl moiety of the first-formed oxadiazoles by the ni trogen nucleophile and/or the solvent also takes place. By the same photoch emical approach, the synthesis of the 3-methoxy-5-pentafluorophenyl-1,2,4-o xadiazole is also described. (C) 2001 Elsevier Science Ltd. All rights rese rved.