Mesoions and ketene valence isomers. Pyrrolo[1,2-a]pyridinylium olates and (2-pyridyl)carbonylketenes

Abstract

The zwitterionic title compounds 5a–d are obtained by FVT of picolinoylacetates 3a–d. Compounds 5a–d undergo nucleophilic addition reactions by C–N bond cleavage to afford pyridine derivatives 6–12. The thermal and photochemical ring opening of 5a to the ketene valence isomer 4a is demonstrated by matrix isolation IR spectroscopy and supported by excellent agreement with DFT calculations.