Asymmetric Construction of Bispiro[oxindole-pyrrolidine-rhodanine]s via Squaramide-Catalyzed Domino Michael/Mannich [3 + 2] Cycloaddition of Rhodanine Derivatives with N-(2,2,2-Trifluoroethyl)isatin Ketimines

Enantioselective Mannich reaction between rhodanines and isatin-derived ketimines to construct vicinal tetrasubstituted stereocenters

An organocatalytic enantioselective Mannich reaction between rhodanines and isatin-derived ketimines was developed. With 2 mol% of a quinine-based tertiary amine-thiourea catalyst C2, 3,3-disubstituted oxindoles with vicinal tetrasubstituted stereocenters were obtained in moderate-to-excellent yields (43-99%) with excellent diastereoselectivities (98 : 2-99 : 1 dr) and good-to-excellent enantioselectivities (up to 97% ee). The readily available substrates, low catalyst loading and high stereoselectivity are the major features.