2,4,6-Trimethylpyridine → 2-Bromoethyl 2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl)-beta-D-galactopyranoside

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Reaction Steps

A solution of the crude acetobromo sugar 49 (20.5 g; 29.3 mmol) in dry methylene chloride (100 ml) was added dropwise (ca 20 min) to a cold (-78°) solution of silver trifluoromethanesulfonate (nonpurified, commercial material; 10.3 g; 40 mmol), 2,4,6-tri-methylpyridine (3.6 g; 30 mmol) and 2-bromoethanol (17.5 g; 140 mmol) in methylene chloride (250 ml) under nitrogen. The reaction mixture was stirred in the dark for 23 h during which time it had reached room temperature. The yellowish-white precipitate, that had formed, was removed and the resulting colorless solution was washed consecutively with 1M hydrochloric acid, water, saturated sodium hydrogen carbonate solution and water. Drying (sodium sulfate), filtration and evaporation gave a residue which crystallized spontaneously. Recrystallization from ethyl acetate, followed by evaporation of the mother liquor and recrystallization from methanol, gave a total of 16.6 g (77%) of the title compound 15. Melting point and optical rotation are shown in Table 1 and the 13C- and 1H-NMR data are shown in Table 2 and 3 , respectively.

Provenance & Evidence