A solution of racemic (2′S,3S,4′R)-6-chloro-4′-[5-chloro-2-(1-hydroxycarbonyl-1-methyl-ethoxy)-phenyl]-2′-(5-fluoro-2-methyl-phenyl)spiro[3H-indole-3,3′-piperidine]-2,6′(1H)-dione (16 g, 0.028 mol) prepared in Example 1f and CDI (9 g, 0.056 mol) in DMF (70 mL) was heated at 65° C. for 2 h. Then to this solution was added a mixture of methanesulfonamide (16 g, 0.168 mol) and NaH (5.6 g, 60%, 0.14 mol) in DMF (100 mL), which had been mixed and stirred at room temperature for 2 h. After the resulting mixture was stirred at room temperature for 2 h, it was poured into water and the aqueous solution was acidified to “pH” 1-2 by addition of concentrated HCl. After the aqueous phase was extracted with EtOAc twice, the combined organic layers were dried over anhydrous Na2SO4, concentrated and the residue was purified by recrystallized to give the title compound (11.4 g).
