Depsidone Synthesis. XXII An Alternative Synthesis of Gangaleoidin

Abstract

A new synthesis ofthe lichen depsidone gangaleoidin (1) (methyl 2, 4-dichloro-3-hydroxy-8-methoxy-1, 6-dimethyl-11-oxo-11H-dibenzo[b, e][1, 4]dioxepin-7-carboxylate) is described. It depends on the oxidation of methyl 4-hydroxy-3-(4ˊ, 6ˊ-dihydroxy-2ˊ-methylbenzoyl)-6-methoxy-2-methylbenzoate (7) to methyl 6-hydroxy-4, 6ˊ-dimethyl-4ˊ-methoxy-2ˊ, 3-dioxo-2, 3-dihydrospiro[benzofuran-2, 1ˊ-cyclo-hexa-3ˊ, 5ˊ-dienel-5ˊ-carboxylate (8), and the thermolysis of this compound to methyl 3-hydroxy-8-methoxy-1, 6-dimethyl-11-oxo-11H-dibenzo[b, e][1, 4]dioxepin-7-carboxy1ate (2), which had been previously converted into gangaleoidin (1) by chlorination. © 1981, CSIRO. All rights reserved.