Synthesis of 4,8-Bis(4-hydroxy-3-methoxyphenyl)-3,7-dioxabicyclooctan-2-ones and Determination of their Relative Configuration via Long-range

Article abstract of DOI:10.1039/P19930000653

A short synthesis of the furofuranoid lignan, 4-cis,8-cis-bis(4-hydroxy-3-methoxyphenyl)-3,7-dioxabicyclo<3.3.0>octan-2-one (MEL), was accomplished via a simple regioselective hydride reduction of the dilactone parent <4-cis,8-cis-bis(4-hydroxy-3-methoxyphenyl)-3,7-dioxabicyclo<3.3.0>octane-2,6-dione>, followed by deoxygenation of the lactone-lactol intermediate via silane hydride transfer.The 4-trans-8-cis(iso-MEL) and the 4-cis-8-trans(epi-MEL) isomers, and a fourth related compound, featuring a 3-fused 5-membered ring skeleton were additionally formed.All four compounds were fully characterized by use of 1D and 2D NMR techniques.Examination of the long-range coupled proton network by delayed COSY experiments allowed determination of the relative configuration of these 4,8-diaryl-3,7-dioxabicyclo<3.3.0>octan-2-one structures.The pathways followed by these long-range proton couplings and implications of the long-range and vicinal couplings with respect to favoured conformations are discussed.