Electron impact ionization mass spectrometry and intramolecular cyclization in 2-substituted pyrimidin-4(3 H)-ones

Electron impact ionization mass spectrometry indicates that the behavior of N-unsubstituted pyrimidin-4-ones with CH 2-R type substitution at C-2 differs from homologs that are N-substituted and/or 2-aryl- or 2-methyl-substituted. A dominant intramolecular cyclization was found to occur between 3 N (in agreement with the predominance of the 3NH tautomers) and the ortho positions of the aryl moiety in compounds with a CH 2-aryl substitution at C-2. Theoretical calculations with an AM1 SCFR method on 2-, 6-, and 2,6-disubstituted pyrimidin-4-ones support the mass spectrometric observations.