Preparation of dibenzocyclooctadiene lignans and spirodienones by hypervalent iodine oxidation of phenolic dibenzylbutyrolactones

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Abstract
Treatment of the dibenzylbutyrolactone 4 with Phl(OCOCF3)2 in trifluoroethanol gives as the major product either the dibenzocyclooctadiene 7a or the spirodienone 8, depending upon the time allowed for the reaction. The structures and stereochemistry of 7a and 8 have been determined by NMR methods and by X-ray crystallography. Reaction of a second dibenzylbutyrolactone 5 under the same conditions gives the products 10–12. These reactions provide the first syntheses of spirodienones such as 8 and 10 which have been postulated as intermediates in the biosynthesis of dibenzocyclooctadiene lignans.

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