Stereoselective Synthesis of Bisfuranoxide (Aurochrome, Auroxanthin) and Monofuranoxide (Equinenone 5′,8′-Epoxide) Carotenoids by Double Horner–Wadsworth–Emmons Reaction

Abstract

The stereoselective synthesis of C40-all-trans-carotenoids with the formal hexahydrobenzofuran skeletons aurochrome, auroxanthin, and equinenone-5′,8′-epoxide is reported. The synthesis is based on a one-pot or stepwise double Horner–Wadsworth–Emmons (HWE) reaction of a terminal enantiopure C15-5,6-epoxycyclohexadienylphosphonate and a central C10-trienedial. The ring expansion of the epoxycyclohexadienylphosphonate, generated by a Stille cross-coupling reaction, to the hexahydrobenzofuran skeleton was promoted by the reaction conditions of the HWE reaction prior to double-bond formation.