3-Aroyl-5-hydroxyflavones: Synthesis and mechanistic studies by mass spectrometry

Article abstract of DOI:10.1002/(SICI)1096-9888(199709)32:9<930::AID-JMS549>3.0.CO;2-E

The synthesis and mass spectra of three 3-aroyl-5-hydroxflavones are reported. The interpretation of the mechanistic pathways for the fragmentation of the metastable molecular ions of these compounds was achieved through the analysis of their mass-analysed ion kinetic energy (MIKE) spectra and of the B²/E spectra of a few fragment ions. Labelling of the hydroxyl proton with deuterium and the analysis of the MIKE spectra of a model compound with chlorine atoms in the 2',6'- and 2',6'-positions led to a mechanism for the losses of OH^. and HCO^. which involves hydrogen migration from the 2'- or 6'-position to the 6-carbonyl oxygen atom. A mechanism for the loss of a neutral molecule of anisole from the molecular ion of the 3-aroyl-5-hydroxyflavone with a methoxyl group in the 4'- and 4'-positions is also suggested. For the flavones with hydrogen or chlorine substituents at these positions, loss of a phenyl (or chlorophenyl) radical occurs instead.