Electron ionisation mass spectral studies of bridgehead-fused Delta2-norbornanethiazolines

The electron ionisation (EI) mass spectra of a series of bridgehead-fused Delta2-norbornanethiazolines, a new class of bridgehead-norbornane derivatives, have been studied and their cleavage mechanisms rationalised on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation tandem mass spectrometric experiments. The fragmentation patterns of isomeric pairs of 6,6- and 10,10-dimethylnorbornanethiazolines are almost identical, probably due to an initial isomerisation of molecular ion previous to the fragmentation. In general, the dominant peaks in the spectra of all the studied compounds originate from initial alpha-cleavages of C(5)-C(6) or C(1)-C(10) bonds, followed by concomitant homolytic cleavage of C(1)-C(9) and C(7)-C(10) bonds. The driving force for this fragmentation pathway, directed by the gem-dimethyl group, is the formation of a highly stabilised thiazolilmethyl cation which constitutes the base peak in all the spectra and allows the identification of these interesting ligands.