Electron-impact mass spectra of substituted 1-alkyl-2-arylsulphonylamino-1,4,5,6-tetrahydropyrimidines

Fragmentation pathways of the title compounds under electron impact were compared to those of their (1-aryl)substituted analogs reported earlier. The main fragmentation route of the M+. ions is the sulphamide N-S bond cleavage leading to [M - ArSO2](+) ions. No loss of the alkyl substituents from the tetrahydropyrimidine ring of M+. ions was observed, but there were abundant (>10% total ion current) peaks of [M - SO2 - R](+) ions apparently formed via unstable [M - SO2](+.) and [M - R](+) species, as demonstrated by the metastable ion spectra, Fragmentation of cyclic alkylguanidinium ions [M - ArSO2](+) involves consecutive losses of CH2N2 and C2H4 fragments, the former process preceding the latter. This stepwise fragmentation pattern distinguishes (1-alkyl)substituted tetrahydropyrimidines from their (1-aryl)substituted analogs, which produced comparable amounts of [M - ArSO2 - C2H4](+) and [M - ArSO2 - CH2N2](+) ions as the precursors of [M - ArSO2 - C3H6N2](+) ions. (C) 1998 John Wiley & Sons, Ltd.