Selective synthesis of methyl dithienyl-glycolates

An efficient selective synthesis of methyl dithienyl-glycolates has been developed. The interest of this two steps protocol resides in the possibility of synthesized either methyl 2,2-dithienyl glycolate – the target intermediate for the preparation of anticholinergic agents – or its regio-isomer methyl 2,3-dithienyl glycolate – the most critical precursor of anticholinergic drug impurity.