INTRAMOLECULAR AROMATIC-SUBSTITUTION AND AMINO-CLAISEN REARRANGEMENT IN SUBSTITUTED N-(2-PROPYNYL)ANILINES ON ELECTRON-IMPACT

N-(2-Propynyl)anilines undergo amino-Claisen rearrangement to a minor extent in the ion source, losing a molecule of HCN under electron impa ct conditions. However, metastable molecular ions with energies closer to threshold undergo Claisen rearrangement giving rise to more abunda nt [M - HCN](+.) ions in the first field-free region, Loss of a hydrog en from the molecular ion gives rise to the base peak in the mass spec trum of N-(2-propynyl)aniline. The hydrogen that is expelled for the f ormation of the [M - H](+) ion is observed to be from the amino nitrog en, propargylic carbon and the ortho-carbon of the ring, The last proc ess leads to a cyclic fragment involving intramolecular aromatic subst itution, Double oxygen migration from the nitro group to the triple bo nd, due to the ortho effect, yields an abundant ion at m/z 105 in N-(2 -propynyl)-o-nitroaniline. The proposed fragmentation pathways and ion structures are substantiated by high-resolution data, B/E and B-2/E l inked-scan spectra, collisionally activated dissociation-B/E linked-sc an spectra and deuterium isotopic labelling.