Reaction of thionyl chloride with 2-acetyl-1- benzenesulfonylpyrrole semicarbazone (6 c) gave 4 - (1- benzenesulfonyl-2 - pyrrolyl) - 1, 2, 3 -thiadiazole (lc). Selenium dioxide oxidation of 2-acetylpyrazine semicarbazone (10) in acetic acid afforded 4- (2-pyrazinyl) - 1, 2, 3- selenadiazole (4). Reaction of thionyl chloride with compound 10 gave 4- (2-pyrazinyl) - 1, 2, 3- thiadiazole (3)....