Dichloromethane → 1,2:5,6-Bis-O-(1-methylethylidene)-alpha-D-allofuranose

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1,2:5,6-di-O-isopropylidene-α-D-glucofuranose 260 g (1 mole) was stirred for 24 h in DMSO 2000 ml and Ac2O 500 ml (5 mole) at RT. By that time, TLC (DCM (dichloromethane)/MeOH 95:5) indicated complete reaction of the starting material. The solution was then cooled to 0° C. and sodium borohydride 16 g (0.42 mole) was added portion wise. By that time, TLC (DCM/MeOH 95:5) indicated complete formation of the target compound, approx. 1 h, water 2500 ml was added and the solution was extracted with DCM 3×1000 mL. The combined organic phases was washed with water 2×1000 ml and brine and dried with magnesium sulfate and evaporated to an oil. To the oil was added tert-butyl methylether (300 mL) and extracted with water 2×750 mL. The combined water phases were extracted with dichloroethane 2×400 mL. The combined organic phases was dried with magnesium sulfate and evaporated to an oil. Crystallisations twice from cyclohexane, 500 ml and 300 ml respectively, gave 151 g (58%) of pure 1,2:5,6-di-O-isopropylidene-α-D-allofuranose.

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