Intramolecular rearrangement of two-ring 2,2-disubstituted 4-oxo-1,2,3,4-tetrahydropyrimidines under the influence of polyphosphoric acid

Intramolecular rearrangement of two-ring 2,3-disubstituted 4-oxo-1,2,3,4-tetrahydropyrimidines to pyridine derivatives, which takes place under the influence of polyphosphoric acid, was observed. It is shown that cycloalkanopyrimidones are converted primarily to two- or three-ring 2-pyridones and to small amounts of the corresponding 4-pyridones and 4-aminopyridines. A possible mechanism that enables one to explain the difference in the occurrence of the rearrangements primarily to 2- or 4-pyridones as a function of the absence or presence of aromatic character of the ring condensed with the pyrimidine ring is proposed.