Transformations of lignans. Part 11: Oxidation of diphyllin with hypervalent iodine reagents and reductive reactions of a resulting 1-methoxy-1-aryl-4-oxonaphthalene lactone

Treatment of diphyllin 4 with phenyliodonium diacetate (PIDA) in methanol affords a 1-methoxy-1-aryl-4-oxonaphthalene lactone 6. Reduction of 6 with lithium aluminium hydride yields, inter alia, 3,4-dihydrodiphyllin 13, while reaction with sodium in ethanol yields 8 as a major product. These reactions illustrate that selective oxidation followed by reduction provides a facile route for the conversion of a 1-arylnaphthalene lactone to novel functionalised naphthalene and dihydronaphthalene derivatives. Of particular interest is that the oxidation indirectly activates the methylene position (C-10) of the γ-lactone, which may then potentially be substituted to give a new series of lignans. Reaction of 6 with hydroxylamine and benzyloxyamine also proceeds by way of initial attack at C-10.