D-Glucal

Preparation of 2,3,4,6-tetra-acetyl-1-bromo-α-D-glucopyranose (9):

Compound 8 (pentaacetylglucose) (10 g, 25.6 mmol) was dissolved in anhydrous dichloromethane (60 mL). Under ice bath conditions, a solution of 33% (w/v) of hydrogen bromide acetic acid (4.9 mL, 2.0 equiv.) was slowly added. The reaction was allowed to proceed at room temperature for 6 hours.

After the reaction was completed, an ice solution of saturated sodium bicarbonate was added to the reaction system to quench the reaction. The mixture was then extracted with dichloromethane and water to obtain an oily compound 9 (10.1 g, 96% yield, mass percentage) Rf 0.6 (PE/EA2/1), which was used directly in the next step. Preparation of 3,4,6-tris-acetyl-glucoseene (10): Compound 9 (5 g, 12.16 mmol) was dissolved in acetone, and zinc powder (7.63 g, 9.6 equiv.) and a saturated NaH2PO4 solution (30 mL) were added at room temperature. The reaction was allowed to proceed for 12 hours at room temperature. Afterward, the mixture was filtered, extracted with dichloromethane and a saturated NaHCO3 solution, dried over anhydrous Na2SO4, and concentrated by rotary evaporation to obtain an oily compound 10 (3.1 g, 94% yield, mass percentage) Rf 0.3 (PE/EA5/1), which was used directly in the next step. Preparation of D-glucoseene (11): At room temperature, MeONa (158.75 mg, 2.94 mmol, 0.4 equiv.) was added to a methanol solution (15 mL) of compound 10 (2 g, 7.35 mmol). The reaction was carried out for 1.5 hours. After the reaction was completed, the pH was adjusted to 7.0 with H+ ion exchange resin, filtered, and concentrated by rotary evaporation to obtain oily compound 11 (1 g, yield 93%, mass percentage).