Regio- and Chemoselectivity of Tandem N-Ketoalkylation/Cyclization of 2-Thioxoimidazoline-4-One

The reaction of 2-thioxoimidazolidin-4-one (thiohydantoin) with aliphatic, aromatic and heteroaromatic alpha-iodomethylketones has been investigated in the absence of bases or catalysts. The reaction proceeds as N-alkylation with subsequent intramolecular dehydrative cyclization. A series of new mono- and fused bicyclic iodide and triiodide salts was obtained based on the 5-oxo-2-thioxoimidazolidin-1-ium and imidazo[2,1-b]thiazolium cations. The observed regioselectivity has been rationalized and the mechanism was proposed.