16378-06-6

5650-52-2

To a suspension of phosphorus pentoxide (P2O5, 25.4 g, 179.0 mmol) in methanesulfonic acid (100 mL) was added 3-(thiophen-3-yl)propionic acid (5.0 g, 32.0 mmol) and the reaction mixture was stirred for 1 hour at room temperature. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure and the residue was purified by fast column chromatography (eluent: 20-30% ethyl acetate/hexane) to afford 4,5-dihydropenta[B]thiophen-6-one (1.34 g, 30% yield) as a brown solid. The structure of the product was confirmed by 1H NMR (300 MHz, MeOH): δ 8.14 (d, J = 4.8 Hz, 1H), 7.17 (d, J = 4.8 Hz, 1H), 2.94-3.15 (m, 4H); mass spectra (EI) m/z = 139.2 [M + 1]+.