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.