[C:1]([O:5][C:6](=[O:14])[C:7]([CH2:12][OH:13])([CH2:10][OH:11])[CH:8]=[CH2:9])([CH3:4])([CH3:3])[CH3:2].N1C=CC=CC=1.Cl[C:22](Cl)([O:24]C(=O)OC(Cl)(Cl)Cl)Cl.[Cl-].[NH4+]>ClCCl>[C:1]([O:5][C:6]([C:7]1([CH:8]=[CH2:9])[CH2:12][O:13][C:22](=[O:24])[O:11][CH2:10]1)=[O:14])([CH3:4])([CH3:2])[CH3:3]A solution of 2,2-bis-hydroxymethyl-but-3-enoic acid tert-butyl ester (202 mg, 1 mmol) and pyridine (0.5 mL, 6 mmol) in dichloromethane (5 mL) was stirred at −78° C. under nitrogen. A solution of triphosgene (150 mg, 0.5 mmol) in dichloromethane (2.5 mL) was added dropwise and the reaction mixture was stirred at −78° C. for 1 h. The reaction mixture was warmed to room temperature and stirred at room temperature for 15 min and saturated ammonium chloride solution was added. The organic layer was separated, washed with hydrochloric acid (1 M), saturated sodium hydrogen carbonate solution and brine. The organic solution was filtered through a hydrophobic frit and the filtrate was evaporated. The residue was purified by silica gel chromatography using a gradient of iso-hexanes/ethyl acetate 4:1 to 3:2 to afford the title compound (204 mg, 89%) as a clear gum. 1H NMR (300 MHz, CDCl3): δ 1.48 (s, 9H), 4.38 (d, J=10.7 Hz, 2H), 4.71 (d, J=10.7 Hz, 2H), 5.39 (d, J=17.4 Hz, 1H), 5.47 (d, J=10.7 Hz, 1H), 5.77 (dd, J=17.4, 10.7 Hz, 1H). LCMS (m/z) 229.1 [M+H], Tr=2.04 min.
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