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

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.