6.10 C-C Bond Formation: Diels-Alder Reaction

The asymmetric Diels-Alder reaction is one of the most powerful organic transformations and is a versatile tool for the synthesis of many bioactive natural products. The asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imino compounds are also among the most powerful methodologies for the construction of optically active heterocycles, and there are extensive applications of these reactions in the synthesis of bioactive natural and unnatural compounds. In addition to conventional Lewis acid catalysis, organocatalysis has been successfully applied to the enantioselective Diels-Alder reaction. Through the use of chiral secondary and primary organoammonium salt catalysts and hydrogen-bonding catalysts, the enantioselective Diels-Alder reaction of dienes with α,. β-unsaturated carbonyl compounds can be promoted. Chiral secondary and primary organoammonium salt catalysts activate α,. β-unsaturated carbonyl compounds via the formation of an iminium cation intermediate, whereas chiral hydrogen-bonding catalysts activate these compounds via coordination of the carbonyl group.