690 mg (6.8 mmol) of triethylamine and 713 mg (4.1 mmol) of diethyl chlorophosphate were added to a solution of 400 mg (3.4 mmol) of (S)-2-methylvaleric acid in 15 ml of dry benzene, and the resulting mixture was stirred at room temperature for one hour. 1.58 g (2.9 mmol) of (4R,6R)-6-{2-[(1S,2S,6S,8S,8aR)-1,2,6,7,8,8a-hexahydro-6-t-butyldimethylsilyloxy-8-hydroxy-2-methyl-1-naphthyl]ethyl}tetrahydro-4-t-butyldimethylsilyloxy-2H-pyran-2-one [prepared as described in Example B, above] and 250 mg (1.7 mmol) of 4-(1-pyrrolidinyl)pyridine were then added to the mixture. The mixture was then stirred at room temperature for 24 hours, after which the mixture was diluted with 20 ml of benzene. The diluted mixture was then washed with 20 ml of water, 20 ml of a 10% w/v aqueous solution of citric acid, a saturated aqueous solution of sodium hydrogencarbonate and a saturated aqueous solution of sodium chloride, in that order. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was removed by distillation under reduced pressure. The resulting residue was purified by flash column chromatography through silica gel, using a 6:1 by volume mixture of hexane and ethyl acetate as the eluent, to give 1.38 g (74% yield) of the title compound.
