Benzylic cleavage and McLafferty rearrangement under electron ionization conditions in the fragmentation of 5,6-dialkyl-2,4-diarylpyrimidines

Several 5,6-dialkyl-2,4-diarylpyrimidines were prepared and their electron ionization (EI) mass spectra reported. The benzylic cleavage takes place ea sily together with an important McLafferty rearrangement. The involvement o f the nitrogen atom appears to be important in the fragmentation of 5-methy l-substituted pyrimidines, In contrast, the 6-methyl-substitute pyrimidines undergo benzylic cleavage without hydrogen transfer. Thus, the difference in the mass spectrometric behaviour allows the identification of these isom eric compounds which, in contrast, exhibit only small differences in their NMR spectra. Copyright (C) 1999 John Whey & Sons, Ltd.