<Review>Asymmetric Diels-Alder Reactions Using Chiral α, β-Unsaturated Sulfoxides as Efficient Dienophiles

This review reports on our recent studies on asymmetric Diels-Alder reactions of chiral α, β-unsaturated sulfoxides. For the preparation of these sulfoxides as Diels-Alder dienophiles, the Andersen method as well as a novel route by diastereoselective oxidation of 2-exo-hydroxy-10-bornyl vinyl sulfides with 3-chloroperoxybenzoic acid is presented. The latter methodology has been successfully applied to synthesis of two types of novel sulfoxides bearing labile fuctionality, I.e., α-sulfinylmaleate and α -sulfinylmaleimide derivatives. These sulfinyl dienophiles effect Diels-Alder reactions with a high degree of diastereoselectivity. Especially, the chiral α-sulfinylmaleimides readily react with Diels-Alder dienes of rather low reactivity, to give the corresponding cycloadducts under conventional conditions. Also described are applications of these asymmetric Diels-Alder reactions to natural product synthesis