The Structure and Synthesis of 4-Oxypannaric Acid 2-Methyl Ester, a Dibenzofuran From the Lichen Leproloma diffusum

Abstract

The structure of the major dibenzofuran present in the lichen Leproloma diffusum has been shown to be that of 4-oxypannaric acid 2-methyl ester (2-methyl hydrogen 3,4,9-trihydroxy-1,7-dimethyldibenzofuran-2,6-dicarboxylate) (2). The structure of (2) was confirmed by total synthesis, achieved through a biomimetic-type approach using palladium(II) acetate in the key cyclization step. Partial synthesis of the corresponding dimethyl ester (8) was effected starting from natural pannaric acid 6-methyl ester (6).