General procedure for the synthesis of tert-butyl (4R,6S)-6-formyl-2,2-dimethyl-1,3-dioxane-4-acetate from (4R,6S)-6-hydroxymethyl-2,2-dimethyl-1,3-dioxane-4-acetate: tert-butyl (4R,6S)-6-hydroxymethyl-2,2-dimethyl-1,3-dioxane-4-acetate ( 10.0 g, 0.0385 mol) was dissolved in a solvent mixture of dimethyl sulfoxide (15.0 g, 0.192 mol) and dichloromethane (100 mL) and the reaction system was subsequently cooled to 0 to -5 °C. After being maintained at this temperature for 15 minutes, diisopropylethylamine (17.42 g, 0.1347 mol) was slowly added and stirring was continued at 0 to -5 °C for 15 minutes. Another flask was taken and a suspension was prepared by sequentially adding pyridine-sulfur trioxide complex (12.25 g, 0.077 mol), pyridine (6.09 g, 0.077 mol) and dimethyl sulfoxide (15.0 g, 0.192 mol) at room temperature and stirring for 10 minutes. This suspension was slowly added to the aforementioned cooled dichloromethane solution, keeping the reaction temperature at 0 to -5°C and continuing to stir for 1 hour. Upon completion of the reaction, the reaction was quenched by the addition of water (50.0 mL) and stirred for 10 minutes. Liquid-liquid separation was then performed and the aqueous phase was back-extracted with dichloromethane (2 x 20 mL). The organic phases were combined, washed sequentially with water (3 x 100.0 mL), dried over anhydrous sodium sulfate, and concentrated under reduced pressure to remove the solvent to give the crude product. The crude product was dried under reduced pressure at 40 to 45 °C for 1 h. The final product was tert-butyl (4R,6S)-6-formyl-2,2-dimethyl-1,3-dioxohexane-4-acetate (9.22 g, 93.0% yield).
