Ring-Contraction of Hantzsch Ester and Derivatives to Pyrrole via Electrochemical Extrusion of Ethyl Acetate out of Aromatic Rings

An electrochemical ring-contraction of HE and its derived pyridine is developed, giving polysubstituted pyrrole. This process provides an orthogonal utilization of Hantzsch ester to the well-documented application as side chain or hydrogen donors. The formal transformation shows an extrusion of ethyl acetate out of the pyridine ring in single step. The reaction provides a number of polysubstituted pyrroles have never been accessed, including the pharmaceutical intermediates and photoswitch. An unusual 4-electron continuous reduction drives the unprecedented anionic dearomatization/ring-contraction/rearomatization pathway. This transformation represents a new utlization of HE with very high atom economy with harmless side product ethyl acetate.