6533b855fe1ef96bd12afd80
RESEARCH PRODUCT
Identity Double-Proton Transfer in (3Z)-3-Hydroxy-1,4-di(quinolin-2-yl)but-3-en-2-one
Borys OśmiałowskiRyszard GawineckiErkki Kolehmainensubject
Chemical shiftOrganic ChemistryQuinolineAb initioGeneral ChemistryNuclear magnetic resonance spectroscopyTautomerCatalysisOxalateTransition statechemistry.chemical_compoundchemistryComputational chemistryPyridinedescription
Although there is a very fast (on the NMR timescale) double-proton transfer in (1Z,3Z)-3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one (the product of the condensation of ethyl oxalate with 2-lithiomethylquinoline), it is the only species present in chloroform solution. Comparison of the product of condensation of ethyl oxalate with 2-lithiomethyl derivatives of pyridine (recent studies) and quinoline (present studies) shows that benzoannulation considerably affects the tautomeric equilibrium. The observed changes are not only quantitative but also qualitative. Moreover, contrary to the proton transfer in the pyridine tautomers, this process is fast in the quinoline tautomers. Comparison of the experimental and ab initio/DFT GIAOcalculated 1 3 C and 1 5 N chemical shifts for the transition states in the protontransfer reactions between (1Z,32)-3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one and its tautomers support the theory that a concerted identity reaction takes place between the enolimine-enaminone and enaminone-enolimine tautomeric forms. As a consequence, the most stable tautomeric form, (1Z,3Z)-1,4-di(quinolin-2-yl)buta-1,3-diene-2,3-diol, is not present in the tautomeric mixture.
year | journal | country | edition | language |
---|---|---|---|---|
2003-05-29 | Chemistry - A European Journal |