Studies on Thiocyanation of Heterocyclic Compounds. III Syntheses of Imidazo-[2, 1-b] benzothiazole and Thiazolo[3, 2-a] benzimidazole Derivatives, and Thiocyanation and Bromination of Their Compounds.

Abstract

2-Methylimidazo [2, 1-b] benzothiazole (III₁) was prepared in a good yield by heating 2-imino-3-(2-propynyl)-2, 3-dihydrobenzothiazole hydrobromide (II) obtained from 2-aminobenzothiazole (I) and propargyl bromide with two equivalent amounts of sodium ethoxide in ethanol. Three kinds of 2-phenylimidazo [2, 1-b] benzothiazoles (III_2-4) were obtained in a good yield by treatment of I with phenacyl bromide in butanol for 2 hr at 110-115°. Thiocyanation of III_1-4 was carried out by the bromine method and the urea method, and the corresponding 3-thiocyanato derivatives (IV_1-4) were obtained in a good yield. 3-Methylthiazolo [3, 2-a] benzimidazole (VIII) was prepared in a good yield from 2-(2- propynylthio) benzimidazole hydrobromide (VII·HBr) and two equivalents of sodium ethoxide. Thiocyanation of VIII and the corresponding 3-phenyl derivatives (X_1-3) did not proceed, the starting materials being recovered, whereas 2-bromo derivatives (XI<1-4>) were obtained in a good yield by bromination of VIII and X_1-3.