Chiral N‐Heterocyclic Carbene‐Catalyzed Asymmetric Michael–Intramolecular Aldol‐Lactonization Cascade for Enantioselective Construction of β‐Propiolactone‐Fused Spiro[cyclopentane‐oxindoles]

A cascade asymmetric Michael–intramolecular aldol‐lactonization of enals with oxindolyl β,γ‐unsaturated α‐keto esters was developed. An optically pure aminoindanol‐derived triazolium‐based N‐heterocyclic carbene was used as the catalyst. The corresponding desired β‐propiolactone‐fused spiro[cyclopentane‐oxindoles] were obtained in moderate yields with excellent diastereoselectivities and enantioselectivities. Notably, the obtained enantio‐enriched highly functionalized complex molecules contain four contiguous stereocenters, including a spiro all‐carbon center and a quaternary carbon center.