A new method has been developed for constructing vicinal quaternary stereocenters with an oxindole–butanolide hybrid framework through asymmetric vinylogous addition of a siloxyfuran to an indol-2-one in the presence of a readily available N,N′-dioxide–Ni(OTf)2 complex catalyst. Various oxindole–lactones were obtained in up to 98% yield with >19:1 dr and 97% ee under mild reaction conditions. A possible transition-state model is proposed to explain the origin of the asymmetric induction.
Key words
asymmetric catalysis - nickel catalysis - ligands - bromooxindoles - lactones - vinylogous addition