Depsidone synthesis. XXII. An alternative synthesis of gangaleoidin

Abstract

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