Transformations of lignans. Part 4: Oxidative and reductive rearrangements of dibenzocyclooctadiene and spirodienone lignans

DDQ oxidation of a dibenzocyclooctadiene derived from a 2,3-dibenzylbutane-1,2,4-triol di-O-methyl ether gives an oxygen-bridged dibenzocyclooctadienone and an oxygen-bridged spirodienone. The same products may also be obtained directly from the dibenzylbutane derivative by treatment with excess DDQ. Acid treatment of the spirodienone leads to demethylation and rearrangement to an ortho-benzoquinone. Reductive rearrangement of the spirodienone produces an oxygen-bridged dibenzocyclooctadienone. These reactions yield unique cyclohexadienone lignans and illustrate readily achieved increases in complexity starting from a simple dibenzylbutane derivative.