Sodium borohydride → (2R,5R)-2-(t-butyl)-5-((1R)-3-hydroxycyclopentyl)-5-phenyl-1,3-dioxolan-4-one

To a solution of 169 mg of the (2R,5R)-2-(t-butyl)-5-((1R)-3-oxocyclopentyl)-5-phenyl-1,3-dioxolan-4-one, as obtained in Step 1 of Referential Example 1, in 2 ml of methanol, 71 mg of sodium borohydride was added under cooling with ice, followed by 30 minutes' stirring at the same temperature. The reaction liquid was diluted with diethyl ether, washed with water and with saturated brine, and dried over anhydrous magnesium sulfate. Distilling the solvent off under reduced pressure, 157 mg of the title compound was obtained as a colorless oily substance.