Mass spectra of some new 3,4-dihydro-2[H]-pyridones

Electrospray ionization (ESI) and tandem mass spectrometry (MS/MS) experime nts, as well as electronic impact (EI) and chemical ionization (CI) techniq ues, have been applied to the title compounds 1a-h. The observation of diff erent fragmentation pathways in the three sets of spectra is in accord with different degrees of internal excitation of the investigated precursors. I n ESI (methanol as solvent) and CI (methane as reagent gas) spectra, the MH + ion represents the most important peak, while the fragments [M - OH](+) a nd [M - SO](+) are either. the base peak or a very abundant peak in the EI mass spectra of these compounds, ESI-MS/MS experiments on the parent ions [ MH](+) show that the loss of a fragment of 140 Da corresponding to p-toluen esulfenic acid is common from all the precursors. As well as competitive pa thways, the second generation ions have also been elucidated to allow some observations to be made concerning the relationships between structure type and mass spectrometric characteristics. Copyright (C) 2000 John Wiley & So ns, Ltd.