Yield:84028-88-6 100%

Reaction Conditions:

with 2,6-dimethylpyridine in dichloromethane at -78 - 20; for 1.66667 h;

Steps:

7 Benzyl 2-deoxy-3-O-((R)-1′-ethoxycarbonylethyl)-4,6-O-benzylidene-2-(allyloxy-carbonylamino)-α-d-glucopyranoside (8)

1.7
Benzyl 2-deoxy-3-O-((R)-1'-ethoxycarbonylethyl)-4,6-O-benzylidene-2-(allyloxy-carbonylamino)-α-d-glucopyranoside (8)
Preparation of (-)-ethyl (S)-2-trifluromethanesulfonyl propionate:
To a solution of (-)-ethyl (S)-2-hydroxypropionate (0.23 mL, 2 mmol) in dry DCM (0.56 mL) was added 2,6-lutidine (236 μL, 2 mmol).
The reaction mixture was kept at -78 °C and Tf₂O (344 μL, 2 mmol) was added dropwise, stirred for 40 min, warmed up to rt and stirred for 1 h.
The mixture was diluted with dry DCM: Hexane ((1:1) 0.7 mL) and filtered through a short silica gel column (approx. pack 1 cm of silica gel pad).
Then the reaction mixture was washed with 0.7 mL of dry DCM: Hexane (1:1) and concentrated to give (-)-ethyl (S)-2-trifluromethanesulfonyl propionate quantitatively.
To a solution of 7 (175 mg, 0.4 mmol) in dry DCM (2.6 mL) was added NaH (35 mg, 1.5 mmol, 60% oil dispersion), stirred for 1.5 h, added more NaH (10 mg, 0.4 mmol) and stirred for 1 h at rt.
The mixture was then treated with neat (-)-ethyl (S)-2-trifluromethanesulfonyl propionate dropwise and stirred for 3 h at rt.
The reaction mixture was quenched by addition of ice and extracted with CHCl₃.
The organic solution was washed with saturated aq NaHCO₃ and brine, dried and concentrated.
The residue was purified by column chromatography (CHCl₃/EtOAc 7:0.5) to give 8 as a white solid (145 mg, 68%). _

References:

Enugala, Ramu;Pires, Marina J.D.;Marques, M. Manuel B. [Carbohydrate Research,2014,vol. 384,p. 112 - 118]