A solution of (2R)-2-[2-(tert-butoxy)-2-oxoethyl]-5-cyclohexylpentanoic acid (Preparation 1) (300 mg, 1.00 mmol) in dichloromethane (15m) was treated with 1,1′-carbonyidiimidazole (162 mg, 1.00 mmol) and the solution was stirred at room temperature for 2 hours. N′-hydroxy-2-(phenylsulfonyl)ethanimidamide (J.Heterocycl.Chem.; 16; 1979; 1197-1200) (214 mg, 1.00 mmol) was then added and the mixture was stirred for 17 hours. The solvent was removed under reduced pressure and the residue was heated neat at 130° C. under a nitrogen atmosphere for 2 hours. The crude product was then purified by column chromatography on silica gel eluting with dichloromethane:methanol (99:1) to afford the title compound (78 mg).
