STEREOCHEMICAL EFFECTS IN THE ELECTRON IONIZATION MASS-SPECTRA OF CYCLOALKANE-(ALKENE)-FUSED 2,3-DIHYDRO-5H-THIAZOLO[3,2-A]PYRIMIDINE-5-ONES AND 3,4-DIHYDRO-2H,6H-PYRIMIDO[2,1-B]THIAZIN-6-ONES

Stereochemical effects on the electron-impact (ET)-induced fragmentati on of cis/trans- and diendo/diexo-fused stereoisomers of several 2,3-d ihydrothiazolo[3,2-a] pyrimidin-5-ones and 3,4-dihydropyrimido[2,1-b]t hiazin-6-ones annelated to various saturated and unsaturated carbocycl es were studied, The retro-Diels-Alder fragmentations of the hydrocarb on rings were found to be of low to medium stereospecificity, A number of highly selective fragmentation processes, some of them involving a McLafferty rearrangement as an initial step, were discovered, and sev eral criteria for the differentiation between stereoisomers of cyclohe xane-, cyclohexene-, norbornane-, and norbornene-fused compounds were proposed, The fragmentation pathways were confirmed by accurate mass m easurements and by metastable ion spectra.