Depsidone synthesis. XXIII. The oxidation of 2,2'-dihydroxy-4,4'-dimethoxy-6,6'-dimethylbenzophenone

Oxidation of 2,2'-dihydroxy-4,4'-dimethoxy-6,6'-dimethylbenzophenone (1) with alkaline ferricyanide gave the expected 4',6-dimethoxy-4,6'-dimethylspiro[benzofuran-2(3H),1'-cyclohexa-3',5'-diene]-2',3(2H)-dione (2) as well as 2'-hydroxy-6-methoxy-4,5'-dimethylspiro[benzofuran-2(3H),1'-cyclopent-4'-ene]-3(2H),3'-dione (3). The structure of compound (3) was deduced from its spectroscopic properties and was confirmed by X-ray diffraction.