Trimethylsilyl triflate → [(5S)-3-(5-bromopyridin-2-yl)-4,5-dihydroisoxazol-5-yl]methyl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside

Participants

Reaction Steps

To a solution of [(5S)-3-(5-bromopyridin-2-yl)-4,5-dihydroisoxazol-5-yl]methanol (Intermediate 11, 0.369 g, 1.43 mmol) and 2,3,4,6-tetra-O-acetyl-1-O-(2,2,2-trichloroethanimidoyl)-α-D-glucopyranose (R. R. Schmidt and J. Michel, Angew. Chem. Int. Ed. Engl. 19 (1980), 731–732) in dry dichloromethane (20 mL) over molecular sieves (perled, 4 Å) was added dropwise at −20° C. a solution of trimethylsilyl trifluoromethanesulfonate in dichloromethane (0.02 M, 10 mL). The reaction mixture was allowed to reach room temperature over 2 hours, additional catalyst solution (5 mL) was added and it was left overnight at room temperature. The reaction was quenched by addition of triethylamine (3 drops), filtered and solvent was removed under reduced pressure. Chromatography on silica gel with hexanes/acetone 2:1 gave crude [(5S)-3-(5-bromopyridin-2-yl)-4,5-dihydroisoxazol-5-yl]methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside, as a mixture with intermediate 11. To a solution of this mixture in dry methanol (5 mL) was added potassium carbonate (20 mg) and it was vigorously stirred for 4 hours at room temperature. The reaction mixture was neutralized over Amberlite CG-50-II (H+-form), filtered and solvent was removed under reduced pressure. Chromatography on silica gel with dichloromethane/methanol 8:1 gave the product as a colourless solid (157 mg).

Provenance & Evidence