Abstract
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A solid support under microwave (MW) irradiation without solvent allowed the synthesis of the 2,3‐epoxy‐propyl‐thioimidazole 4, regioselectively, and prohibited its cyclization to give the imidazo[2,1‐b]thiazine 3 from the reaction of 4,5‐diphenylimidazole‐2‐thione (1) with 1‐chloro‐2,3‐epoxy‐propane (2). The formation of the latter required basic conditions whereby it became the sole product; the change of the basic catalyst changed the ratio of the two products under both conventional and microwave (MW) conditions. A regioselective allylation of 1 with allyl bromide in presence of triethylamine gave the S‐allyl 8, while in presence of potassium carbonate led to the S,N‐bis(allylated) derivative 9. The intramolecular ring closure of 8 in presence of sulfuric acid afforded the imidazothiazole 16. Protection of the sulfur in 1 and subsequent reaction with allyl bromide gave the N‐allylated derivative and with 2 gave N‐3‐chloro‐prop‐1‐yl derivative that shed light on the preferred route for the formation of 3 and 4. The reactivity encountered during the alkylation of 1 with 2 has been theoretically investigated by using the AM1 method.