Potassium Carbonate → 2,2-Dimethyl-propionic acid (2S,3S,4R,5R)-3,5-dimethoxy-2,4-dimethyl-hept-6-ynyl ester

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To 2,2-Dimethyl-propionic acid (2S,3S,4R,5R)-3,5-dimethoxy-2,4-dimethyl-6-oxo-hexyl ester (2.0 g, 6.94 mmol) in anhydrous methanol (100 ml) at 0° C. and under an atmosphere of nitrogen was added diethyl 1-diazo-2-oxopropylphosphonate (1.6 ml, 10.4 mmol) and potassium carbonate (1.44 g, 10.4 mmol). The reaction was stirred at 0° C. for 1 hour and then room temperature for 2 hours, after which it was quenched with saturated ammonium chloride and extracted with diethyl ether (3×). The combined organic layers were dried over magnesium sulphate, filtered and concentrated in vacuo. The product was purified by flash chromatography (SiO2, iHex/EtOAc, 15:1) to afford 1.67 g (85%) as a clear oil. 1H NMR (300 MHz, CDCl3) δ 4.22 (dd, J=10.7 Hz, 3.6 Hz, 1H), 4.07 (dd, J=10.7 Hz, 5.8 Hz, 1H), 3.87 (dd, J=9.6 Hz, 2.0 Hz, 1H), 3.46 (s, 3H), 3.44 (m, 1H), 3.40 (s, 3H), 2.48 (d, J=2.0 Hz, 1H), 1.97 (m, 2H), 1.23 (s, 9H), 1.00 (d, J=6.9 Hz, 3H), 0.92 (d, J=6.9 Hz, 3H).

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