Two-Step Regioselective Synthesis of 3-(Sulfonylamino)imidazo[1,2-a]pyrimidines from 2-Aminopyrimidines and N-(2,2-Dichloro-2-phenylethylidene)arensulfonamides

The reaction of 2-aminopyrimidines with N-(2,2-dichloro-2-phenylethylidene)arenesulfonamides 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 give imidazo[1,2-a]pyrimidin-3-ylsulfonamides in the presence of NaOH, whereas the expected isomeric imidazo[1,2-a]pyrimidin-2-ylsulfonamides are not formed. A tentative mechanism for the formation of annulated heterocyclic derivatives through Dimroth rearrangement has been proposed.