Synthesis of N-Substituted Pyrrole-2,5-dicarboxylic Acids from Pyrroles

Pyrrole-2,5-dicarboxylic acid (PDCA) is a heterocyclic aromatic dicarboxylic acid that may emerge as a new monomer for polyester production. Compared to its structurally related and bio-based furan-2,5-dicarboxylic acid (FDCA) that is already used for the production of polyethylene furanoate (PEF), PDCA shows excellent potential as its nitrogen can be targeted for further derivatization, thus enabling tuning of the properties of a PDCA containing polymer. In light of this, we recognized the need to explore efficient synthetic approaches for producing PDCAs in high yields. Here, we report a five-step synthesis route for N-substituted PDCAs starting from pyrrole, with total yields up to 42 %. The synthetic approach allowed the introduction of several different functional moieties to the pyrrole nitrogen, such as aliphatic saturated and unsaturated side-chains, as well as benzylic groups.