Hans Bosshard

Dimethyl-Maleic Anhydride, A New Synthesis and Versatile Uses of an Old Compound

Abstract Maleic anhydride and many of its derivatives are valuable starting materials for heterocyclic synthesis. However, dimethyl-maleic anhydride has hitherto been a rather expensive and not readily accessible compound. Our new two-step (one-pot) synthesis now permits the preparation of dimethyl-maleic anhydride with an overall yield of 70–80%. The starting material is maleic anhydride, which is converted to dimethyl-maleic anhydride with the help of a tautomerisable amino-substituted heterocyclic compound. The reactivity of dimethyl-maleic anhydride, which differs considerably from that of maleic anhydride, is illustrated by some examples. This different reactivity is due to the repulsive steric interactions of the (Z)-vicinal methyl groups, as confirmed by single crystal X-ray analysis. Simple reduction of dimethyl-maleimides leads to hydroxy-pyrrolones, which show interesting herbicidal properties.