To a stirring 20°-25° C. solution of the (4R-cis)-1,1-dimethylethyl 6-hydroxymethyl-2,2-dimethyl-1,3- dioxane-4-acetate (European Patent Application 0319,847) (10 g, 0.038 mol) in methylene chloride (250 mL) containing triethylamine (7 mL, 0.05 mol) is added 4-nitrobenzenesulfonyl chloride (10.5 g, 43 mmol). Stirring is continued at 20°-25° C. for 22 hours, the solution is poured onto 200 mL of water and the layers separated. The upper aqueous layer is extracted with 250 mL of methylene chloride and the combined organic layers are washed with 100 mL each of saturated sodium bicarbonate solution to ensure complete removal of 4-nitrobenzenesulfonyl chloride and then saturated sodium chloride solution. Drying the solution with magnesium sulfate and concentration in vacuo gives 18.7 g of the product as a brown oil which solidifies immediately.
