Synthesis and properties of new heterocyclic betaines: 4-Aryl-5-(methoxycarbonyl)-2-oxo-3-(pyridin-1-ium-1-yl)-2,3-dihydro-1H-pyrrol-3-ides

Abstract New heterocyclic betaines, 4-aryl-5-(alkoxycarbonyl)-2-oxo-3-(pyridin-1-ium-1-yl)-2,3-dihydro-1H-pyrrol-3-ides, were synthesized in good yields by the reaction of alkyl 2H-azirine-2-carboxylates with 2-methoxy-2-oxo-1-(pyridin-1-ium-1-yl)ethan-1-ides, generated from the corresponding pyridinium salts. The betaines exist as the NH-tautomers both in solution and in the solid state. Two molecules of the betaine form a dimer by hydrogen bonds of the type N H⋯O in solid state. According to TD DFT calculations the long-wave absorption band in betaines mainly corresponds to the intramolecular charge transfer between the negatively charged pyrrole unit and the positively charged pyridinium group. The blue shift of the long-wave absorption in protic solvents was adequately described in terms of H-complex formation with the nucleophilic centre of the molecular skeleton.