Ethyl chloroformate → Carbonic acid (1R,2S,3S,4R,5S)-5-[4-chloro-3-(4-ethoxy-benzyl)-phenyl]-2,3,4-trihydoxy-6,8-dioxa-bicyclo[3.2.1]oct-1-ylmethyl ester ethyl ester

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To a vigorously stirred solution of (1S,2S,3S,4R,5S)-5-[4-chloro-3-(4-ethoxy-benzyl)-phenyl]-1-hydroxymethyl-6,8-dioxa-bicyclo[3.2.1]octane-2,3,4-triol (1A, 288 mg, 0.659 mmol) in collidine (6.6 mL) cooled to −35 degrees Celsius was added drop-wise over 10 minutes ethylchloroformate (0.112 mL, 1.19 mmol). The reaction mixture was allowed to stir overnight at room temperature. The reaction was quenched with an aqueous solution of saturated citric acid and extracted with ethyl acetate (2 times). The combined organic layers were washed with brine, dried over magnesium sulfate, filtered and concentrated under reduced pressure. The crude material was purified by flash chromatography over silica gel using the biotage automated chromatography unit (50 g silica gel column) and eluting with a gradient of 0 to 20% methanol in dichloromethane. 134 mg (40% yield) of desired product as a white solid.

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