Methanol → (2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanal

To a solution of the crude triacetyl glucal 3 (9.54 g, 35.0 mmol) in CH3CN (150 mL) was successively added LiBr (3.65 g, 42.0 mmol), MeOH (2.25 g, 70.2 mmol), and p-toluenesulfonic acid monohydrate (p-TsOH.H20, 954 mg) at room temperature. After being stirred for 3 h, the reaction mixture was concentrated to a small volume, diluted with cold 5% NaHCO3 solution, and extracted with CHCl3. The organic extract was washed with ice-water, dried over MgSO4, and evaporated in vacuo. The residue was chromatographed on silica gel (150 g) using 30% AcOEt-hexane to give 8 (9.01 g, 92% from D-glucose) (α-anomer:β-anomer=ca. 10:1). 8a was isolated as a single isomer, while 8b was obtained as a mixture of 8a and 8b.