Phenylacetaldehyde → 2-Phenyl-1-(thiophene-2-sulfonylamino)-ethyl-phosphonic Acid Diethyl Ester

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To a suspension of sulfonamide (vi) (500 mg; 0.31 mmol) in acetyl chloride (5 mL) was slowly added diethyl phosphite (400 μL; 0.31 mmol). The reaction was cooled to 0° C. and then phenylacetaldehyde (450 μL; 0.39 mmol) was added dropwise. The reaction was gradually warmed to ambient temperature and after 6 hrs the homogeneous solution was concentrated. The residue was diluted with dichloromethane (25 mL) then washed successively with water (10 mL), saturated sodium bicarbonate (10 mL) and brine (10 mL). The combined organic extracts wre dried (MgSO4), evaporated and initially purified by flash chromatography (ethyl acetate-hexanes; 3:2). A second purification by flash chromatography (acetone-hexanes; 3:7) yielded diethyl phosphonate (xii) (437 mg, 35%) as a colorless solid; 1H NMR (400 MHz, CDCl3) δH 1.22 (t, J=7 Hz, 3H, OCH2CH3), 1.26 (t, J=7 Hz, 3H, OCH2CH3), 2.89 (dt, J=8, 14 Hz, 1H, CHPh), 3.12 (dt, J=6, 14 Hz, 1H. CHPh), 3.96-4.23 (m, 5H, NCHP and OCH2CH3), 6.38 (dd, J=2, 9.5 Hz, 1H, NH), 6.92-6.93 (m, 1H, Ar—H), 7.12-7.20 (m, 5H, Ar—H), 7.33-7.34 (m, 1H, Ar—H), 7.43-7.45 (m, 1H, Ar—H).

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