A new class of fused imidazoles by intramolecular nucleophilic ipso-substitution in 2-alkylsulfonylimidazoles: Synthesis of 2,3-dihydroimidazo[2,1-b][1,3]oxazoles

Starting from readily available thiouronium salts 1 and alpha-halocarbonyl compounds 2, a simple and efficient synthesis of 2-alkylthioimidazoles 3 wa s accomplished. Reduction of the carbonyl group, followed by oxidation of t he 2-alkylthioether moiety, afforded sulfones 8. Intramolecular nucleophili c ipso-substitution in 2-alkylsulfonylimidazoles 8 efficiently furnished a novel class of fused imidazoxazoles. This finding was extended towards the generation in solution of a small library of 2,3-dihydroimidazo[2,1b][1,3]o xazoles.