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In dichloromethane; at 20℃; for 1.5h;Inert atmosphere;Kinetics; |
General procedure: To a 10-mL, single-necked, round-bottomed flask fitted with a magnetic stir-bar, a nitrogen inletadapter and with a rubber septum was added diastereomerically pure 2,3,4,6-tetra-O-benzylglucosyltrichloroacetimidate 1 (alpha to yield beta product or to yield alpha product, 50 mg, 0.073 mmol)as a waxy glass followed by dry CH2Cl2 (0.75 mL, 0.03 M). The resultant suspension was stirredvigorously until it was a homogeneous, clear, colorless solution (ca. 30 min). To the resultantsolution was added carboxylic acid (0.077 mmol, 1.05 equiv) as a solid in a single portion. Theresulting clear solution was stirred at room temperature and monitored by TLC (20%EtOAc/Hexanes), then concentrated by rotary evaporation (15 mm Hg, 20-25 oC) after thereaction was judged to be complete. To the crude material (waxy glass) was added CH2Cl2 (5mL). After a further 30 min of stirring the solution was concentrated again by rotary evaporation(15 mm Hg, 20-25 oC). The resultant mucilaginous suspension was purified by flashchromatography on silica as follows; the crude material was loaded onto a pre-packed (2 x 8 cm,Si-gel, EtOAc/Hexanes (2/98) slurry, 15 psi) column as a suspension (CHCl3/Hexanes, 1/1, 2-3mL), rinsing with EtOAc/Hexanes (2/98). The column was then run with a gradient of increasingpolarity (EtOAc/Hexanes), as indicated in the individual procedures at no more than 5 psi. Thediastereomerically pure fractions were combined and triturated to a fine powder with hexanes. |