ROLE OF LACTAM VS. LACTIM TAUTOMERS IN 2(1H)-PYRIDONE CATALYSIS OF AROMATIC NUCLEOPHILIC-SUBSTITUTION

3-Ethylaminocarbonyl-2(1H)-pyridone 1 and 3-ethoxycarboqyl-2(1H)-pyrid one 2 have been synthesised and tested as catalysts for the aromatic n ucleophilic substitution of fluoride by piperidine in 2-fluoro-5-nitro benzonitrile 3. A kinetic model which takes into account the dimerisat ion of the catalysts has been developed, which allows a quantitative a nalysis of measured data. 3-Ethylaminocarbonyl-2(1H)-pyridone 1 exists exclusively as a lactam tautomer, either monomeric or dimeric but 3-e thoxycarbonyl-2(1H)-pyridone 2 exists as a lactim monomer, whereas its dimer exists in the lactam form. Despite such differences, these two compounds exhibit similar catalytic efficiencies for the reaction stud ied, suggesting that lactim and lactam tautomers have comparable effic iencies in tautomeric catalysis.