Asymmetric synthesis of spiro[4H-chromene-3,3′-oxindoles] via a squaramide-organocatalytic three-component cascade Knoevenagel/Michael/cyclization sequence
摘要
Asymmetric synthesis of spiro[4H-chromene-3,3′-oxindole] derivatives was realized through an organocatalytic cascade Knoevenagel/Michael/cyclization reaction using a quinidine-derived squaramide. Under the optimized conditions, the reactions of isatins, malononitrile, and sesamol yield the desired spirooxindoles in good yields (75–87%) and moderate to high ee values (up to 90% ee).