Asymmetric Synthesis of Spiro-epoxyoxindoles by the Catalytic Darzens Reaction of Isatins with Phenacyl Bromides

The asymmetric Darzens reaction between phenacyl bromides and N-protected isatins was developed to synthesize potentially bioactive spiro-epoxyoxindoles. The optically active products were obtained in moderate to good yields and enantio-selectivities catalyzed by chiral N,N'-dioxide-Co(acac)(2) complexes. A retro-aldol process accompanying the ring-closure step was observed in the process. A chiral control step was determined to be the initial aldol addition.