Regioselectivity of the reactions of 4,5-diphenylimidazole-2-thione with 1-chloro-2,3-epoxy-propane and 1-bromo-propene, efficient precursors for imidazo[2,1-b]thiazine and thiazole.: Effect of microwave and solid support

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 I with allyl bromide in presence of triethylamine gave the S-allyl 8, while in presence of potassium carbonate led to the SN-bis(allylated) derivative 9. The intramolecular ring closure of 8 in presence of sulfuric acid afforded the imidazothiazole 16. Protection of the sulfur in I and subsequent reaction with ally] bromide gave the N-allylated derivative and with 2 gave N-3-chloroprop-1-yl derivative that shed light on the preferred route for the formation of 3 and 4. The reactivity encountered during the alkylation of I with 2 has been theoretically investigated by using the AMI method.