光学活性α, β-不飽和スルホキシドを用いる不斉ディールス・アルダー反応と天然物合成への応用

Abstract

Chiral sulfoxides have provided useful methods for asymmetric carbon-carbon bond formations. Among them chiral α, β-unsaturated sulfoxides have offered effective dienophiles in asymmetric Diels-Alder reactions. In the continuation of this study aiming at exploring a conceptually new approach to such sulfoxides, we focused on a (2-exo-hydroxy-10-bornyl) sulfinyl moiety instead of a p-tolylsulfinyl group which has widely been employed as a chiral auxiliary. The use of this chiral auxiliary (i. e. (2-exo-hydroxy-10-bornyl) sulfinyl) realized not only a facile preparation of chiral α, β-unsaturated sulfoxides but also the synthesis of chiral α-sulfinylmaleate and α-sulfinylmaleimide derivatives which effected Diels-Alder cycloadditions with high diastereoselectivity. Especially the α-sulfinylmaleimides readily reacted with the Diels-Alder dienes with rather low reactivity such as furan, to afford the corresponding Diels-Alder adducts under conventional conditions. The chirally functionalized adducts derived from the Diels-Alder reactions were transformed into some, biologically important natural products.