A regioselective [4 + 2] annulation approach to 5-acylindolizine-7-carbonitriles: generation of poly-substituted pyridines.

The reaction of β-ketonitrile and N-substituted pyrrole-2-carboxaldehyde in the presence of piperidinium acetate in CH3CN permitted regioselective access to 5-acylindolizine-7-carbonitrile through a domino Knoevenagel condensation-intramolecular aldol cyclization sequence. A wide range of new indolizine derivatives with a poly-functionalized pyridine moiety were readily synthesized in an atom-economical fashion, thereby expanding the indolizine chemical space for further applications.