Umpolung Strategy for\nthe One-Pot Synthesis of Highly\nSteric Bispirooxindoles via the l‑Amino Acid Ester-Promoted\nIn Situ Reduction/Nucleophilic Addition/Cyclization Cascade Reaction

On the basis of a novel umpolung\nstrategy, an efficient l-amino acid ester-mediated in situ\nreduction of 2-(2-oxoindolin-3-ylidene)malononitrile\nand sequential nucleophilic addition/cyclization cascade reaction\nis reported. Various densely substituted cyclopentene bispirooxindoles\nand dihydrofuran bispirooxindoles with two quaternary spirocenters\nwere constructed in high yields (≤93%) with excellent diastereoselectivities\n(>20:1 dr). The method has advantages of readily available starting\nmaterials, mild reaction conditions, a one-pot process, a metal-free\nbiomimetic reducing agent, a wide substrate scope, and operational\nsimplicity (single filtration without column chromatography).