Depsidone synthesis. Part 15. New metabolites of the lichen Buellia canescens(Dicks.) De Not: novel phthalide catabolites of depsidones

Abstract

The isolation, from the lichen Buellia canescens(Dicks.) De Not., and structural determination of the new depsidones 2,7,9-trichloro-3-hydroxy-8-methoxy-1,6-dimethyldibenzo[b,e][1,4]dioxepin-11-one (dechlorodiploicin)(1) and its methyl ether dechloro-O-methyldiploicin (9), together with the novel phthalides 4-chloro-7-(3,5-dichloro-4,6-dimethoxy-2-methylphenoxy)-5-methoxyisobenzofuran-1(3H)-one (buellolide)(13) and 4,6-dichloro-7-(2,4-dichloro-3,6-dimethoxy-5-methylphenoxy)-5-methoxyisobenzofuran-1(3H)-one (canesolide)(18) are described. The synthesis of buellolide (13) is also described. It is postulated that buellolide (13) and canesolide (18) arise by catabolism of their congeneric depsidones, in the latter case with Smiles rearrangement.