Asymmetric Synthesis of Spiro[4H-Chromene-3,3′-oxindoles] via Squaramide-Organocatalyzed Three-Component Cascade Knoevenagel/ Michael/ Cyclization Sequence

An efficient stereoselective three-component reaction for the synthesis of spiro[4H-chromene-3,3’-oxindole] derivatives was realized through an organocatalyzed cascade Knoevenagel/Michael/cyclization reaction using a quinidine-derived squaramide as the catalyst. 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). Two pairs of selected enantiomers were subjected to evaluate their antiproliferative activities on three types of human cancer cell lines using the MTT assay. The results indicated that stereoselectivity and electrical effect showed significant impact on activity. Enanotiomer R-3f exhibited optimal cytotoxic activity against U2OS cell line, which was close to the inhibitory activity of positive control, Adriamycin.