A mixture of EXAMPLE 2 in pyridine (9 mL/g) at 0° C. was treated with a mixture of para-methoxybenzenesulfonyl chloride (1.05 equivalents) in THF (1.4 mL/g) at 0° C. at a rate which kept the reaction temperature below 5° C., warmed to 25° C., stirred for 15 minutes, and concentrated. The concentrate was treated with n-propanol to provide a composition having 9% pyridine in the solvent mixture and to precipitate a solid. The mixture was cooled to 0° C. and filtered. The filtrant and washed with ethyl acetate (5-7 mL/g starting material) and dried at 45° C.
