Biaryl sulfonamides from O‐acetyl amidoximes: 1,2,4‐Oxadiazole cyclization under acidic conditions

A series of 4-cyanobenzenesulfonamides (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h) was converted to the corresponding O-acetylated amidoximes (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h). The reaction of 1a was exemplarily investigated with respect to the formation of a byproduct, which was identified as 1,2,4-oxadiazole derivative 3a. This observation led to the development of an improved procedure for the preparation of 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h. Compounds 2 could be transformed to 1,2,4-oxadiazoles 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h in high yields and purity upon heating in acetic acid. J. Heterocyclic Chem., (2011).