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, 38 mmol) in methylene chloride) (250 mL) containing triethylamine (10 mL, 72 mmol) is added 4-bromobenzenesulfonyl chloride (15 g, 57.5 mmol). Stirring is continued at 20°-25° C. for 20 hours, the solution is poured onto 250 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 200 mL each of saturated sodium bicarbonate solution, to ensure complete removal of 4-bromobenzenesulfonyl chloride and then saturates sodium chloride solution. Drying the solution with magnesium sulfate and concentration in vacuo gives 26.3 g of the product as a light orange solid.
