Heterocyclization of 2-(Propargylsulfanyl)-1,3-thiazole Derivatives by the Action of Halogens

Reactions of 2-(propargylsulfanyl)-5-methyl-1,3,4-thiadiazole, N-5-(propargylsulfanyl)-1,3,4-thiadiazol- 2-yl]benzamide, 2-(propargylsulfanyl)-1,3-benzothiazole, and 2-(propargylsulfanyl)-4,5-dihydro-1,3- thiazole with iodine involved annulation of the unsaturated substituent with formation of fused thiazole ring. 2(5)-(Propargylsulfanyl)-1,3,4-thiadiazole derivatives reacted with bromine to give mixtures of heterocyclization products and bromine adducts to the triple bond. The bromination of 2-(propargylsulfanyl)-4,5-dihydro- 1,3-thiazole afforded only the bromine addition product to the triple bond.