Brønsted Acid Catalyzed Asymmetric Diels–Alder Reactions: Stereoselective Construction of Spiro[tetrahydrocarbazole-3,3′-oxindole] Framework

The chiral phosphoric acid catalyzed asymmetric Diels–Alder reactions of 2-vinylindoles with methyleneindolinones have been established, which efficiently construct the spiro­[tetrahydro­carbazole-3,3′-oxindole] architecture with one quaternary and three contiguous stereogenic centers in high yields (up to 99%) and excellent stereoselectivities (up to >95:5 dr, 97% ee). This reaction not only provides an efficient strategy to access enantioenriched spiro­[tetrahydro­carbazole-3,3′-oxindoles] based on hydrogen-bonding activation mode but also supplies successful examples of catalytic asymmetric Diels–Alder reactions for constructing complex spiro-frameworks with optical purity.