The Pyridylketenyl Anion: Entry to Diverse N-Heterocycles

The pyridylketene has previously been isolated via matrix isolation and demonstrated potential in the synthesis of N-heterocycles. Herein, we report the synthesis and isolation of the pyridylketenyl anion through conventional synthetic methods, involving metalation and subsequent carbonylation of the readily available 2-pyridyl ylide. Quantum chemical calculations reveal extensive delocalization of the negative charge across the entire molecular framework, resulting in multiple nucleophilic sites that are best described by a series of resonance structures. IR spectroscopic and X-ray diffraction data corroborate this electronic structure, indicating a markedly compressed C-C-C-O moiety. The pronounced charge delocalization enables diverse reactivities and promotes cyclization pathways involving the pyridine nitrogen. Accordingly, the pyridylketenyl anion serves as a versatile precursor for the construction of heterocycles featuring triazolone, quinolizine, and indolizine motifs, underscoring its broad applicability as a building block in heterocycle synthesis.