Asymmetric Lignan Synthesis: Isolariciresinol Dimethyl Ether

Article abstract of DOI:10.1021/jo00368a018

An asymmetric synthesis of the lignan (+)-isolariciresinol dimethyl ether 1 in nine steps and 13percent yield (83percent optical purity) from veratraldehyde is described.Veratraldehyde was converted to 6-(3,4-dimethoxybenzyl)veratraldehyde 3 by bromination, acetal formation, metalation, and coupling to 3,4-dimethoxybenzyl bromide. 3 was irradiated in the presence of SO2 to give the 3-hydroxy-1-aryl-1,3-dihydrobenzothiophene 2,2-dioxide 4, which was converted to the (R)-1-phenylethoxy derivative 5b. 5b on heating with dimethyl fumarate gave a mixture of primarily two diastereomeric cycloadducts 7b and 7b', both of which had the 1,2-trans, 2,3-trans , 3,4-cis stereochemistry.The major adduct 7b was subsequently assigned the stereochemistry 1S,2R,3S,4S.Separation and hydrogenolysis of the major adduct gave the diester 8, 1S,2R,3R, which was reduced with LiAlH4 to give (+)-isolariciresinol dimethyl ether 1.A racemic synthesis was also carried out via the methoxy sulfone 5a and its trans isomer 5a' in 33percent yield.