Stereoselective Syntheses of Cis- and Trans-Isomers of alpha-Hydroxy-alpha,beta-dibenzyl-gamma-butyrolactone Lignans: New Syntheses of (+/-)-Trachelogenin and (+/-)-Guayadequiol

Cis- and trans-isomers of alpha-hydroxy-alpha,beta-dibenzyl-gamma-butyrolactone lignans 1a,d-g and 2a,c,d were stereoselectively synthesized in good yields based on the electrophilic addition to the metal enolate of alpha-benzyl-gamma-butyrolactone derivatives 1l-o and 3 as a key step. This method was applied to the syntheses of (+/-)-trachelogenin and (+/-)-guayadequiol, representative examples of the trans- and cis-isomers of alpha-hydroxy-alpha,beta-dibenzyl-gamma-butyrolactone lignan series.