[CH2:1]([O:8][C:9](=[O:17])[CH2:10]P(OC)(OC)=O)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Li+].[OH-].CC[O:22][C:23]([CH3:25])=[O:24].Cl.[CH2:27]1[CH2:31]OC[CH2:28]1>>[CH2:1]([O:8][C:9](=[O:17])[CH:10]=[C:27]1[CH2:31][CH:25]([C:23]([OH:22])=[O:24])[CH2:28]1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A mixture of cyclobutaneone-3-carboxylic acid (5 g, 43.82 mmol), benzyl-2-(dimethoxyphosphoryl)acetate (13.58 g, 52.59 mmol), LiOH (4.20 g, 23.95 mmol) and 3 Å activated molecular sieves (25 g, powder form) in THF (250 ml) was heated to reflux under nitrogen for 4 h. The reaction was allowed to cool to RT and EtOAc (100 ml) followed by HCl (1N, 100 ml) were added. This mixture was filtered through celite. The phases were separated and the aqueous layer was extracted with EtOAc (4×50 ml). The combined organic layers were dried over Na2SO4, filtered and concentrated to yield a colorless oil. Dry flash chromatography over SiO2, eluting with Hept:EtOAc from 7:3 to 1:1 gave the desired product as a colorless oil (5.2 g, 39%); MS (ESI+) for C14H14O4 m/z 269.05 [M+Na]+; MS (ESI−) for C14H14O4 m/z 245.15 [M−H]−; HPLC purity 81% (ret. time, 1.85 min); 1H NMR (250 MHz, CHLOROFORM-d) δH ppm 2.95-3.62 (5 H, m), 4.96-5.31 (2 H, m), 5.75 (1 H, t, J=2.21 Hz), 7.27-7.45 (5 H, m).
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