Fast-atom bombardment mass spectrometry of new polydentate Schiff bases .5. The case of bis-aldimines containing oxamide groups

Four macrocyclic tetraimine Schiff bases containing oxamidic groups were synthesized by [2+2] condensation of N,N'-bis(2- aminoethyl)oxamide or N,N'-bis(2-amino-1,1-dimethylethyl)oxamide with 2,6-diformyl-4-chlorophenol or 2,6-diformyl-4-methylphenol and characterized by elemental analyses and IR and NMR spectrometry; their [2+2] cyclic nature was inferred (especially) by fast-atom bombardment (FAB) mass spectrometry. The FAB-induced fragmentation patterns of the protonated molecules, investigated with the aid of metastable ion studies, evidence characteristic behaviours related to the presence of oxamidic groups or of 1,1-dimethylethyl species. (C) 1997 by John Wiley & Sons, Ltd.