General procedure for the synthesis of (2S,3S,4R,5R,6R)-6-(acetyloxymethyl)-3-hydroxytetrahydro-2H-pyran-2,4,5-triyl triacetate from 1,2-O-(1-ethoxyethylidene)-β-D-mannopyranose triacetate: to a solution of anhydrous acetone (27 mL) of the protoacid ester (4.4 g, 12 mmol), a slow addition of a 1 M aqueous hydrochloric acid (HCl) solution (2.7 mL), and the reaction was carried out under vigorous stirring (the water bath temperature was maintained at about 18 °C). The reaction mixture was continued to be stirred at room temperature for 5 min before being concentrated on a rotary evaporator, keeping the temperature below 20 °C. The concentrated solid was dissolved in chloroform (CHCl3, 25 mL) and washed with deionized water (2 x 10 mL). The organic phase was dried over anhydrous sodium sulfate (Na2SO4) and filtered, and the filtrate was concentrated on a rotary evaporator. The residue was ground with ether (Et2O) and recrystallized from ethanol (EtOH) to give the target product tetraacetylmannose (1.9 g, 45% yield) as a white solid. Thin layer chromatography (TLC) Rf value was 0.13 (unfolding agent: hexane/ethyl acetate = 1:1). The melting point is 134-136°C. High Resolution Mass Spectrometry (HRMS-ESI): m/z C14H20NaO10 ([M+Na]+) Calculated value 371.09542, measured value 371.09581 (error 0.39 mmu, 1.06 ppm).
