Reactions of quinones with aromatic ethers. Part III. Arylbenzoquinones and dibenzofurans from 2,5- and 2,6-dichlorobenzoquinone and veratrole

Abstract

2,5-Dichlorobenzoquinone reacts with veratrole in 70% v/v aqueous sulphuric acid to form 2,5-dichloro-3-(3,4-dimethoxyphenyl)-1,4-benzoquinone (III; X = H, Y = Cl), 2,5-dichloro-3,6-bis-(3,4-dimethoxyphenyl)-1,4-benzoquinone [III; X = 3,4-(MeO)₂C₆H₃, Y = Cl], and 1,4-dichloro-7,8-dimethoxydibenzofuran-2-ol (IV; X = H, Y = Cl). Similar reactions with 2,6-dichlorobenzoquinone give 2,6-dichloro-3,5-bis-(3,4-dimethoxyphenyl)-1,4-benzoquinone [III; X = Cl, Y = 3,4-(MeO)₂C₆H₃], 1,3-dichloro-7,8-dimethoxydibenzofuran-2-ol (IV; X = Cl, Y = H), and 1,3-dichloro-7,8-dimethoxy-4-(3,4-dimethoxyphenyl)dibenzofuran-2-ol [IV; X = Cl, Y = 3,4-(MeO)₂C₆H₃]. In both cases the veratrole oxidation products 2,3,6,7,10,11-hexamethoxytriphenylene (I) and 2,5,6,9,12,13-hexamethoxydibenzo[fg,op]naphthacene-1,10-quinone (II) are also obtained. The dibenzofurans result from the acid-catalysed cyclisation of the corresponding arylbenzoquinones; similar cyclisations can be effected by visible light.