A solution (0.2 M) of methyl 5-(4-chlorophenyl)-4H-thieno[3,2-b]pyrrole-2-carboxylate in acetic acid was treated with acetic anhydride (2.5 eq.), cyclohexanone (10 eq.) and 85% phosphoric acid (2.1 eq.). The mixture was heated at 80° C. for 3.5 days. After cooling down it was poured into ice cold ammonium hydroxide. The product was extracted with AcOEt and the combined organic layers were washed sequentially with aqueous HCl (1 N), aqueous NaHCO, (saturated solution) and brine then dried and concentrated. The crude was purified by flash chromatography on silica gel (1:9 to 1:4 AcOEt/petroleum ether) affording the title compound (91%) as a solid.
