CYCLOADDITIONS OF 3,4-DIMETHOXYFURAN WITH BENZOQUINONES

Cycloadditions of 3,4‐dimethoxyfuran with benzoquinones Cycloaddition of 3,4‐dimethoxyfuran (3,4‐DF, 1) with 1,4‐benzoquinones furnishes isolable (2 + 4)‐adducts in high yield. The crystalline products with benzoquinone, 2‐methyl‐benzoquinone, 2,3‐dimethoxy‐benzoquinone have endo‐configuration, whereas 2,3‐dimethyl‐benzoquinone gives the exo‐adduct 4c exclusively. Halogens (Cl2, Br2) add rapidly across the highly nucleophilic double bond of 3 or 4 in stereospecific cis‐manner, and exclusively from the exo‐side. The product 5c shows no sign of enolization to the hydroquinone; but with 3a and 3d the hydroquinones 6 were found. Methanolysis of 5 leads to the stable acetals 7 and 8. On oxidation of the hydroquinones 7 the thermolabile quinones 10 were obtained. Preparative pyrolysis of 10a under relatively mild conditions (N2, 200°, 0.1 Torr) gives tetramethoxy ethene (11) and isobenzofuran‐4,7‐quinone 12, a yellowish, crystalline and stable compound. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim