First Stereocontrolled Syntheses of Unsymmetrically Substituted Bislactone Lignans: Stereocontrolled Syntheses of Four Possible Isomers of Methyl 4,8-Dioxoxanthoxylol

An efficient method for stereocontrolled syntheses of the unsymmetrically substituted bislactone subgroup of the furofuran lignan has been developed based on a stereoselective aldol reaction of the acid anhydride 8 or 9 and an aromatic aldehyde employing methyl 4,8-dioxoxanthoxylol ( 1a ), 4,8-dioxofargesin ( 1b ), methyl 4,8-dioxopiperitol ( 2a ) and their isomer 3a as the representative examples of the axial−equatorial 1, diequatorial 2, and diaxial 3 types of this series.