Synthesis of N-Substituted Pyrrole-2,5-Dicarboxylic Acids from d-Galactaric Acid.

Pyrrole-2,5-dicarboxylic acid (PDCA) and its N-substituted derivatives are interesting building blocks for macromolecular applications. However, only a few published procedures describe the synthesis of PDCA derivatives. These procedures often suffer from low yields, the formation of unwanted side products, harsh reaction conditions, the use of toxic and expensive reagents, or the unavailability of certain derivatives. Here, a facile and scalable six-step synthetic route is described, starting from biobased d-galactaric acid, for the production of N-alkylated and N-arylated PDCAs, achieving total yields of up to 45%. In addition, the E-factor of the presented synthesis route is decreased by a factor of 14 compared to already established methods.