4.1. Synthesis of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose (1)

A solution of d-glucose (5 g, 27.78 mmol) in dry acetone (250 ml) was added concentrated sulfuric acid (1.2 ml) at room temperature. The reaction mixture was stirred vigorously at room temperature for 6 h. Anhydrous copper(II) sulfate (15 g) was added to the reaction mixture and stirring was continued at room temperature for 18 h. The reaction mixture was then neutralized with sodium bicarbonate and the inorganic materials were filtered off. The filtrate was evaporated under reduced pressure to leave a white solid, which was partitioned between CH₂Cl₂ and H₂O. The organic layer was dried over Na₂SO₄, filtered and evaporated under reduced pressure providing the title compound as a white solid. Recrystallization from hexane gave the pure diacetal.