Trichloroacetonitrile → 2,5-dimethyl-3-oxo-(2H)-furan-4-yl 2,3,4-tri-O-(4-methoxybenzyl)-alpha-L-fucopyranoside

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The solution of 2,3,4-tri-O-(4-methoxybenzyl)-L-fucopyranose trichloroacetimidate (a/β mixture, prepared from 85 mmol of 2,3,4-tri-O-(4-methoxybenzyl)-L-fucopyranose and trichloroacetonitrile in the presence of NaH in quantitative yield) in diethyl ether (100 ml) was added to a mixture of 2,5-dimethyl-4-hydroxy-3-oxo-(2H)-furan (85 mmol) and TMS-triflate (1.2 ml) in diethyl ether (200 ml) at −14° C. After 3 hours the cooling bath was removed and the stirring continued for 1 hour. The reaction mixture was diluted with ethyl acetate and extracted with sat. NaHCO3-solution (3×150 ml) and brine (150 ml). The organic phase was dried over Na2SO4 and evaporated. The resulting syrup was purified by column chromatography yielding 23.27 g of 2,5-dimethyl-3-oxo-(2H)-furan-4-yl 2,3,4-tri-O-(4-methoxybenzyl)-α-L-fucopyranoside as a thick yellow syrup in a 1:1 mixture of diastereoisomers. Selected NMR chemical shifts in CDCl3: anomeric protons: 5.32 and 5.57 ppm, J1,2=3.4 Hz; anomeric carbons: 113.81 and 113.95 Hz.

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