MASS-SPECTRA OF SOME NEW HETEROCYCLES - CYCLOBUTAPYRIMIDINES AND THEIR DIELS-ALDER ADDUCTS WITH C-60

The electron impact mass spectra of new compounds, 2,4-dialkyl and 2,4 -diaryl substituted-5,6-dihydrocyclobuta[d]pyrimidines, are reported. The main fragmentation pathway leads to the formation of cyclobutadien e [C4H4](+) m/z = 52 as the base peak. The FAB spectra of the adducts of cyclobutapyrimidines with C-60 have also been recorded. In these sp ectra the dominant peaks are formed by a retro-Diels-Alder reaction an d by the apparent loss of the substituents attached at the pyrimidine, ring forming the ions m/z = 720 and m/z = 825, respectively. (C) 1998 John Wiley & Sons, Ltd.