Magnesium sulfate (160 g, 1.33 mol) and concentrated sulfuric acid (9.9 mL, 190 mmol) were added to a solution of (2S,3R,4S)-2,3,4,5-tetrahydroxyvaleraldehyde (99.0 g, 659 mmol) in acetone (1.2 L) at room temperature. The reaction mixture was stirred for 12 hours. After completion of the reaction, filtration was carried out and the filter cake was washed with acetone (300 mL x 2). The filtrates were combined and the pH was adjusted to 7 with 25% ammonia, at which point a solid precipitated and filtered again. The solids were washed with acetone (150 mL x 2). All the filtrates were combined and concentrated under reduced pressure to afford the target product (3aS,3bR,7aS,8aS)-2,2,5,5-tetramethyltetrahydro-3aH-[1,3]dioxolo[4',5':4,5]furo[3,2-d][1,3]dioxolane (Ib) as a yellow oil (128.0 g, 84.3% yield).
