Regioselective synthesis of 3-(heteroaryl)-iminothiazolidin-4-ones

Cyclization of unsymmetrical thioureas affords 3-(heteroaryl)-iminothiazolidin-4-ones with excellent levels of regiocontrol. In the absence of base, 2-(pyridylmethyl) and 2-(aminomethyl)benzimidazolyl substituents on the thiourea scavenge acid that is generated upon sulfur alkylation with bromoesters. The resulting conjugate acid plays an important role in influencing the regiochemical outcome and overall rate of the reaction.