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
1. Department of Chemistry, Faculty of Science, University of Science and Technology —Mohamed Boudiaf;2. Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt;3. International Center for Chemical Sciences, HEJ Research Institute, University of Karachi, Karachi, Pakistan
Abstract:
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.
