CYCLO-ADDITION REACTIONS WITH 3,4-DIMETHOXYFURAN

On cycloaddition reactions with 3,4‐dimethoxyfuran We describe new cycloadditions of 3,4‐dimethoxyfuran (3,4‐DF, 1) with various dienophiles. In contrast to furan, the reaction of 3,4‐DF with maleic anhydride gives exo‐ and endo‐adducts at approximately the same rate. The thermodynamically more stable product is again the exo‐product. Less active dienophiles lead also to mixtures of exo‐ and endo‐adducts, except for citraconic anhydride (methylmaleic anhydride) which forms only the adduct with an endo‐methyl group. Dimethylmaleic anhydride could not be reacted with 3,4‐DF. All adducts with 3,4‐DF contain a hidden 1,2‐dicarbonyl group in the form of an endiolether. Its pronounced nucleophilic character allows a series of further additions. Noteworthy are the stereospecific cis‐additions of halogens and the preparation of several acetals. Ozonolysis of the enolether in 4 allows the preparation of the hitherto unknown 2r, 3trans, 4trans, 5cis‐tetrahydrofuran tetracarboxylic acid and derivatives thereof (5 and 6). Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim