To a solution of racemic (2′R,3R,4′S)-6-bromo-4′-(3-chlorophenyl)-2′-(1-methyl cyclopropyl)-2,3-dihydro-2,6′-dioxospiro[indole-3,3′-piperidine]-1-methoxyethyl trimethylsilane (200 mg, 0.34 mmol) and allyl bromide (1.2 g, 10 mmol) in DMF (15 mL) was added Cs2CO3 (4 g, 12.1 mmol). The mixture was stirred at room temperature for 2 h, then poured into water (100 mL), extracted with ethyl acetate for 3 times. The organic layer was washed with water, dried over Na2SO4, concentrated to give crude product as a light yellow solid (210 mg).
