2,2-Dimethoxypropane → 2-[(4R, 6S)-2,2-dimethyl-6-benzoyloxymethyl-1,3-dioxan-4-yl]acetic tert-butyl ester

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To a solution composed of 8.94 g (27.6 mmol) of (5S)-6-benzoyloxy-3,5-dihydroxyhexanoic tert-butyl ester produced in Example 15, 35.8 mL of 2,2-dimethoxypropane, and 2.5 mL of methylene chloride was added 269 mg (1.4 mmol) of p-toluenesulfonic acid-1H2O, and the mixture was stirred at 20° C. for 4 hours, after which 500 mL of saturated sodium hydrogen carbonate solution was added. The aqueous layer was separated and further extracted with 2 portions of methylene chloride, 20 mL each, and the organic layers were combined. The combined solution was dehydrated over anhydrous sodium sulfate and the solvent was distilled off under reduced pressure to give a colorless oil. This residue was purified by silica gel column chromatography (Kieselgel 60, product of Merck; hexane:acetone=10:1) to give 7.24 g of 2-[(4R,6S)-2,2-dimethyl-6-benzoyloxymethyl-1,3-dioxan-4-yl]acetic tert-butyl ester (white solid). Yield: 72%.

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