A solution (0.2 M) of methyl 6-benzyl-5-phenyl-6H-thieno[2,3-b]pyrrole-2-carboxylate in acetic acid was treated with acetic anhydride (10 eq.), cyclohexanone (10 eq.) and 85% phosphoric acid (2.3 eq.). The mixture was heated at 80° C. for 3 h, then was poured into ice cold ammonium hydroxide. The product was extracted with AcOEt and the combined organic phase was washed sequentially with aqueous HCl (1 N), aqueous NaHCO3 (saturated solution) and brine then dried and concentrated. The crude was purified by flash chromatography on silica gel (1:30 acetone/toluene) affording the title compound (95%) as a solid.
