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.