Reaction Steps
A solution of DABCO (11.8 g, 0.105 mol) in anhydrous toluene (300 cm3) was heated at reflux for 1 hour with continual stirring. The solution was allowed to cool to room temperature, to which (±)-3-iodo-2-cyclopenten-1-ol (6) (6.35 g, 30.4 mmol) was added. Following this, trimethylsilyl chloride (4 mL) was added slowly, after which the reaction mixture was allowed to stir for 15 minutes. On the side, a solution of ethyl butylphosphinate (3) (21.0 g, 0.140 mol) in DCM (150 cm3) was dried over anhydrous sodium sulfate, filtered and the solvent removed in vacuo. Following this, ethyl butylphosphinate (6.83 g, 45.5 mmol) and tetrakis(triphenylphosphine)palladium(0) (876 mg, 2.5 mol %) were then added to the reaction mixture. The reaction mixture was heated at 70° C. for 24 hours after which a second portion of tetrakis(triphenylphosphine)-palladium(0) (876 mg, 2.5 mol %) was added and heating continued for a further 24 hours. The reaction mixture was filtered while still hot and aqueous ethanol (100 cm3), followed by acetic acid (10 cm3) were added to the filtrate, which were then concentrated in vacuo. The product was isolated by short column vacuum chromatography on silica gel (10% ethanol/ethyl acetate) to yield the title compound (7) as a pale yellow oil (4.74 g, 67%; 4.45 g, 63%): 1H-NMR (300 MHz, CDCl3) δH 0.87 (3H, 2×t, J=7.2 and 7.2 Hz & 7.2 and 7.2 Hz, PCH2CH2CH2CH3), 1.17-1.89 (10H, m, C(5)—H′, POCH2CH3, PCH2CH2CH2CH3, PCH2CH2CH2CH3, PCH2CH2CH2CH3), 2.37 (2H, m, C(5)—H and C(4)—H′), 2.62 (1H, m, C(4)—H), 3.45 (1H, br. s, C(3)—OH), 4.02 (2H, m, POCH2CH3),4.95 (1H, m, C(3)—H), 6.62 (1H, d, J=9.7 Hz, C(2)—H); 13C-NMR (75 MHz, CDCl3) δC 13.45 (s, PCH2CH2CH2CH3),16.39 and 16.47 (d, 3JPOCC=6.23 Hz, POCH2CH3), 23.32 and 23.36 (d, 2JPC=3.38 Hz, PCH2CH2CH2CH3), 23.64 and 23.86 (d, 3JPC=15.98 Hz, PCH2CH2CH2CH3), 27.10 and 28.30 (d, JPC=90.23 Hz, PCH2CH2CH2CH3), 31.65 and 31.80 (d, 3JPC=11.70 Hz, C(4)), 33.89 and 33.95 (d, 2JPC=4.58 Hz, C(5)), 60.55 (s, POCH2CH3), 76.61 and 77.03 (d, 3JPC=31.58 Hz, C(3)), 136.94 and 138.51 (d, JPC=117.3 Hz, C(1)), 148.81 (s, C(2)); 31P-NMR (121 MHz, CDCl3) δP 43.93 and 44.18; MS (CI, CH4) m/z 233.1 (100%) (MH+), 215.2 (47), 464.9 (39), 261.2 (18). Synthesis of (±)-ethyl [3-(t-butyldimethylsilyloxy)cyclopentenyl]butylphosphinate (8)
