Microwave-enhanced efficient regioselective synthesis of 1,3,4-trisubstituted 2-mercaptoimidazoles on a soluble support

A novel efficient synthetic method for regioselective synthesis of optically active 2-mercapto-imidazoles with three points of structural diversity was investigated on a polyethylene glycol (PEG) support. The key synthetic steps involve (i) synthesis of thiourea derivatives of polymer-supported amino acids with isothiocyanates and (ii) one-pot regioselective condensation of PEG-linked thiourea with abromo ketones to furnish the 2-mercaptoimidazole skeleton under microwave conditions. An excellent regioselectivity was observed during this one-pot condensation reaction which was further supported by NOE studies. In addition to three sets of structural diversity, supplementary chirality at the a-position of the 2-mercaptoimidazole skeleton is the key feature of this synthesis. A representative set of 2-mercaptoimidazoles was efficiently assembled on soluble support utilizing various l-amino acids, isothiocyanates and a-bromoaryl ketones with good yields.