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

✍ Scribed by Kalevi Pihlaja; Marja Himottu; Ferenc Fülöp; I. Huber; Gábor Bernáth; Vladimir Ovcharenko

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 511 KB
• Volume: 10
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/(sici)1097-0231(199604)10:6<721::aid-rcm543>3.0.co;2-s

✦ Synopsis

Stereochemical effects on the electron-impact (El)-induced fragmentation of cis/trans-and diendo/diexo-fused stereoisomers of several 2,3dihydrothiazolo[3,2+]pyrimidin-5-ones and 3,4-dihydropyrimido[2,1-b]thiazinh n e s annelated to various saturated and unsaturated carbocycles were studied. The retro-Diels-Alder fragmentations of the hydracarbon rings were found to be of low to medium stereospecficity. A number of highly selective fragmentation processes, some of them involving a McLafferty rearrangement as an initial step, were discovered, and several criteria for the differentiation between stereoisomers of cyclohexane-, cyclohexene-, norbomane-, and norbomene-fused compounds were proposed. The fragmentation pathways were confumed by accurate mass measurements and by metstable ion spectra.