To a solution of 2,2-difluoro-2-(1-hydroxy-3,3,5,5-tetramethylcyclohexyl)acetic acid (3.192 g) and Et3N (4.44 mL) in THF (100 mL), ethyl chloroformate (1.12 mL) was added at room temperature and the mixture was stirred for an hour. To the reaction mixture, a THF (50 mL) solution of the compound (2.607 g) obtained in Example 2-(3) was added dropwise at room temperature and the mixture was stirred at room temperature for 64 hours. To the reaction mixture, saturated aqueous sodium bicarbonate (200 mL) was added and the organic layer extracted with AcOEt (200 mL) was washed with brine (200 mL), dried (MgSO4), filtered and concentrated to give a crude product, which was further purified by NH-form silica gel chromatography (AcOEt/hexane); the resulting compound was recrystallized (Et2O/pentane) to give the titled compound (2.969 g, colorless powder.)
