Reaction #163504

Reaction equation

2-O-acetyl-3,4,6-tri-O-benzyl-α-D-mannose

sodium methoxide

→

2-O-acetyl-3,4,6-tri-O-benzyl-α-D-mannose

3,4,6-tri-O-benzyl-α-D-mannose

Yield 127.1%

Solvents

methanol

methanol

Conditions

Workup

1. 1
   OtherAfter ˜2 hours the starting material was consumed
2. 2
   OtherThe reaction was quenched with Amberlite IR120 (H+) resin
3. 3
   Filtrationfiltered
4. 4
   Concentrationconcentrated to a syrup

Procedure

2-O-acetyl-3,4,6-tri-O-benzyl-α-D-mannose was prepared as described in Mayer et al., Eur J. Org. Chem. 10:2563 (1999). 25% w/v sodium methoxide in methanol (0.5 mL) was added to a solution of 2-O-acetyl-3,4,6-tri-O-benzyl-α-D-mannose (8.0 g, 23.3 mmol) in anhydrous methanol (50 mL). After ˜2 hours the starting material was consumed as shown by thin layer chromatography (TLC). The reaction was quenched with Amberlite IR120 (H+) resin, filtered, and concentrated to a syrup to give 3,4,6-tri-O-benzyl-α-D-mannose 50 (6.67 g, 99%). To compound 50 was added toluene (150 mL) followed by dibutyltin oxide (3.88 g, 16.28 mmol), and the mixture was heated under reflux for 3 h using a Dean-Stark condenser. The resulting solution was cooled, concentrated to a syrup, and dissolved in dry DMF (50 mL). Cesium fluoride (2.28 g, 12.1 mmol), tetrabutylammonium iodide (5.47 g, 14.8 mmol), and methyl 4-bromocrotonate (2.46 mL, 22.2 mmol, tech grade) were added to the mixture and heated to −60° C. for 18 hours. The mixture was allowed to cool and the solid filtered off. It was diluted with isopropyl ether/EtOAc 3.7:1 (380 mL) and washed with semi-saturated sodium thiosulphate (240 mL). The aqueous phase was extracted with isopropyl ether/EtOAc 3.7:1 (2×190 mL) and the organic layers pooled and concentrated. The syrup was stripped with isopropanol (2×25 mL), and purified by flash column chromatography using a EtOAc in hexanes 0-50% to afford 51 as a syrup (4.58 g, 56.4%). 13C-NMR (100 MHz) 1J1C,1H (100 MHz), 157 Hz β<160 Hz, α>170 Hz)

Source