Some 5-unsubstituted acetylenic and vinylic 1,2,4-oxadiazoles
3-trans-Styryl-1,2,4-oxadiazoles (2) have been prepared by treating unsaturated amide oximes with trialkyl orthoformates or dimethylformamide dimethyl acetal, and from 1,2,4-oxadiazol-3-ylmethylene(triphenyl)phosphonium chloride (12). Phenylpropiolamide oxime with formyl fluoride gives 3-phenylethynyl-1,2,4-oxadiazole which, on nitration, gives as the main product 3-p-nitrophenylethynyl-1,2,4-oxadiazole (4; R = NO2). This compound has been converted into (4; R = Cl). p-Chlorophenylpropiolonitrile gives only 3-amino-5-p-chloro-phenylisoxazole (15) when treated with hydroxylamine, trans-3-(2- and -3-Thienyl)acrylonitrile react more readily with hydroxylamine than do the cis-acrylonitriles. Some cis-3-styryl-1,2,4-oxadiazoles have been obtained from the corresponding trans-compounds by photoisomerization.