exo-Selective Diels-Alder Reaction Catalyzed by a Chiral Ammonium Salt

Significance

An organocatalytic asymmetric Diels-Alder reaction is described. The ammonium salt of chiral α,α-diarylprolinol silyl ether 1 and TFA mediate the cycloaddition of aromatic as well as aliphatic α,β-unsaturated aldehydes 2 and cyclopentadiene (3) to give bicyclic products of type 4 in good yields, exo-selectivities, and enantioselectivities. Acyclic dienes 6 can also be used, which lead to the formation of optically active functionalized cyclohexenes 7.