Electron ionization-induced loss of a methyl radical from 1-cyclopropyl-4-substituted-1,2,3,6 tetrahydropyridine derivatives

The electron ionization mass spectra of 1-cyclopropyl-4-substituted-1,2,3,6-tetrahydropyridine derivatives are characterized by a base peak corresponding to [M-15]+. Evidence is presented to support a fragmentation process involving an initial cyclopropyl ring opening of the parent cyclopropylaminyl radical cation followed by intramolecular transfer of a hydrogen atom from the ring carbon atoms α to nitrogen to the primary carbon-centered radical and finally a fragmentation step proceeding by loss of a methyl radical and formation of a stable N-ethenyldihydropyridinium ion, the [M-15]+ fragment.