Transformation of 2,3-dibenzylbutyrolactone lignans containing a secondary hydroxyl group to phenyltetralin lignans and their reduction products with lithium aluminum hydride

Two 2, 3-dibenzylbutyrolactone lignans containing a secondary hydroxyl group at one of the benzylic positions, 5-hydroxyarctigenin (I) and 5-hydroxytrachelogenin (XI), were transformed to phenyltetralin lignans, α-conidendrin monomethyl ether (II) and 3-hydroxy-α-conidendrin monomethyl ether (XII), respectively, by acid treatment. The hemiacetal lignan, (1S, 2R, 3S, 3aR) 6, 7-dimethoxy-3-hydroxy-2-hydroxymethyl-1-3', 4'-dimethoxyphenyl-1, 2, 3, 4-tetrahydronaphthalene-3-carboxylic acid lactol (XV), was obtained in addition to isoolivil dimethyl ether (XIV), the normal reduction product, when 3-hydroxy-α-conidendrin dimethyl ether (XIII) was treated with lithium aluminum hydride, and a mechanism is proposed for this reaction.