1H and 13C n.m.r. studies have proved that ethyl 9-dimethylaminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a] pyrimidine-3-carboxylates (2)-(5) and the corresponding pyrrolo homologue (6) exist in the form of E-isomers whereas the azepino[1,2-a]pyrimidine derivative (7) appears as an equilibrium mixture of Z- and E-isomers. On the basis of 15N chemical shifts an analogous tautomeric structure has been established for the 9-dimethylaminomethylene derivatives (2)-(7) and the ethyl 9-arylaminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a] pyrimidine-3-carboxylates (8)-(12) as well. 15N Shifts were sensitively affected by the Z-E isomerism and structural changes in remote parts of the molecule, too. Protonation of compounds (2)-(12) takes place on the N(1) atom, forming a 1,6,7,8-tetrahydro structure.
|Number of pages||4|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - Jan 1 1983|
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