Asymmetric Diels-Alder Reaction of 2-Methyl-3-indolylmethanols via in Situ Generation of o-Quinodimethanes

An asymmetric Diels-Alder reaction of 2-methyl-3-indolylmethanols and alpha,beta-unsaturated aldehydes has been developed that relies on in situ generation of active indole-2,3-quinodimethane intermediates under mild acidic conditions and uses a secondary chiral amine as iminium activation catalyst. An array of highly enantioenriched tetrahydrocarbazoles have been efficiently produced in fair to good yields.