A solution of 2,4-dideoxy-1-O-[(1,1-dimethylethyl)dimethylsilyl]-3-O-[(4-methoxyphenyl)methyl]-2,4-dimethyl-L-arabinitol (10.77 g, 28.19 mmol), DMSO (30 mL), NEt3 (11.39 g, 112.76 mmol) and methylene chloride is cooled to −10° C., and treated with SO3-Pyr (13.45 9, 84.58 mmol)in DMSO (60 mL) over 40 min. After additional 2 h at 0° C., the mixture is diluted with ether (300 mL), washed with 1 M aqueous NaHSO4 (100 mL), brine (100 mL), and concentrated. Flash chromatography (5% ethyl acetate in hexane) gives the desired compound (9 g, 84%) as a colorless oil.
