Unprecedented 8,9′-Neolignans: Enantioselective Synthesis of Possible Stereoisomers for Structural Determination

Abstract

(+)-Wutaienin (<b>3</b>) and its C-7 methyl ether (<b>4</b>), isolated from <i>Zanthoxylum wutaiense</i>, were found to be unprecedented 8,9′-neolignans containing an (<i>S</i>)-2-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydro­benzofuran skeleton. Wutaienin (<b>3</b>) was present in the plant as an inseparable 1:1 mixture of the (7,8)-<i>syn</i>-diastereoisomers. The diastereoisomeric mixture was characterized by comparison with four possible diastereoisomers, which were enantioselectively synthesized from (<i>S</i>)-5-bromo-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydro­benzofuran using Evans’ oxazolidinone-assisted asymmetric aldol condensation to install the chiral centers at the C-7 and C-8 positions