One‐Pot Synthesis of N ‐(Imidazo[1,2‐ a ]pyridin‐3‐yl)‐ and N ‐(Imidazo[2,1‐ b ][1,3]thiazol‐5‐yl)sulfonamides

The reaction of 2‐aminopyridines or 2‐aminothiazole with N ‐(2,2‐dichloro‐2‐phenylethylidene)arensulfonamides affords the corresponding products of nucleophilic addition to the azomethine group, N ‐[2,2‐dichloro‐2‐phenyl‐1‐(heterylamino)ethyl]sulfonamides, in good yields. The latter are easily cyclized to (imidazo[1,2‐ a ]pyridin‐3‐yl)sulfonamides and (imidazo[2,1‐ b ]thiazol‐5‐yl)sulfonamides in the presence of alkali, whereas the expected isomeric (imidazo[1,2‐ a ]pyridin‐2‐yl)sulfonamides and (imidazo[2,1‐ b ]thiazol‐6‐yl)sulfonamides are not formed. A one‐pot two‐stage method for the synthesis of target heterocyclic compounds without the isolation of intermediates has been developed. A tentative mechanism of the formation of annulated heterocyclic derivatives has been proposed.