An Ireland−Claisen Approach to Lignans:  Synthesis of the Putative Structure of 5-epi-Eupomatilone-6

Abstract

A novel Ireland-Claisen approach to the putative structure of eupomatilone-6 is described. The rearrangement established the C3 and C4 stereocenters and concomitantly generated a vinyl epoxide. The C5 oxygen was installed by cyclization of the pentenoic acid carboxyl group onto the vinyl epoxide in an S(N)2' fashion to afford the C5-epi stereochemistry. The natural C5 stereochemistry was accessed via a substrate directed dihydroxylation.

Brønsted Acid-Catalyzed Allylboration: Short and Stereodivergent Synthesis of All Four Eupomatilone Diastereomers with Crystallographic Assignments

“…Eupomatilones exist under ambient conditions as equilibrating couples of biaryl atropisomers. Previous synthetic studies have raised ambiguities on the relative stereochemistry of the lactone's three substituents, − as originally assigned by NMR spectroscopy . Our route to all four diastereomers of 1 , supported with thorough X-ray crystallographic evidence, provides closure on the eupomatilones' stereochemical determination.…”

Gymnothelignans A–O: Conformation and Absolute Configuration Analyses of Lignans Bearing Tetrahydrofuran from Gymnotheca chinensis

“…laurina, , respectively. Owing to their attractive structures, there have been total syntheses of all of the members of eupomatilones − except eupomatilone-1. The absolute configuration of eupomatilone-6 has only just been recently proposed .…”

Tandem Enyne Metathesis and Claisen Rearrangement: A Versatile Approach to Conjugated Dienes of Variable Substitution Patterns

“…In propionates 20 , silyl ketene acetal formation under standard conditions (LiHMDS, TBSCl THF/HMPA, −78 °C) was problematic and resulted in poor conversions. We overcame these difficulties using the conditions described by McIntosh (KHMDS/TMSCl, toluene, −78 °C) to give more efficient silyl ketene acetal generation, thereby obtaining the Claisen product in 82% yield. Esterification using TMSCHN 2 gave the methyl ester S- 21 , which was used for analysis.…”

“…Application. Chiral cyclohexadiene diol derivatives are versatile intermediates used in the synthesis of many natural products . Enantioselective oxidation of monosubstituted benzenes using P. putidia are very powerful, providing access to 3-substituted-3,5-cyclohexadiene-1,2-diols (see J ) .…”