Intramolecular benzyl cation transfer in the fragmentation of Cinchona alkaloid-based quaternary ammonium cations

The fragmentation reactions of Cinchona alkaloid-based quaternary ammonium cations were characterized by collision-induced dissociation mass spectrometry. Besides the common elimination of water and the formation of benzyl cations, the title compounds show two distinct fragmentation reactions resulting from intramolecular benzyl cation transfer. In one channel, the benzyl cation is transferred from the initial site (nitrogen) to the hydroxyl group leading to elimination of the corresponding benzyl alcohol. In another channel, precursor ion first dissociates into an intermediate ion–neutral complex consisting of the benzyl cation and the neutral partner. The intra-complex electrophilic aromatic substitution through benzyl cation attack leads to the formation of protonated benzylquinoline. Such dissociation occurs after the benzyl group migrates from a site with the highest benzylation nucleophilicity (nitrogen) to a different one (hydroxylic oxygen or aromatic ring carbon), which is a typical example of dissociative benzyl cation transfer.

Figure optionsDownload high-quality image (129 K)Download as PowerPoint slideHighlights
► Benzyl cation transfers from the initial site to the hydroxyl group leading to loss of the corresponding benzyl alcohol.
► The intra-complex electrophilic aromatic substitution through benzyl cation attack leads to the formation of protonated benzylquinoline.
► We found two typical examples of dissociative benzyl cation transfer.