Investigation of coordination of Mg(II) cations to 2-pyrimidinyloxy-N-arylbenzylamines by electrospray mass spectrometry: insights for Mg(II) catalyzed Smiles rearrangement reactions

An unexpected acid-catalyzed decomposition reaction of cilnidipine and pranidipine to the decarboxylative bridged tricyclic products via cascade rearrangements

A gas-phase Carroll rearrangement occurring during electrospray ionization tandem mass spectrometry led to the discovery of bridged tricyclic degradation products from cilnidipine and pranidipine.

Study of the gas-phase intramolecular aryltrifluoromethylation of phenyl(trifluoromethyl)iodonium by ESI-MS/MS

The gas-phase reactions of the reactive λ(3)-phenyl(trifluoromethyl)iodonium (PhI(+)(III)CF3, 1 at m/z 273) to the radical cation of iodobenzene (PhI(•+), 2 at m/z 204) via the loss of ·CF3 and the radical cation of trifluoromethylbenzene (PhCF3(•+), 3 at m/z 146) via the loss of ·I, were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Interestingly, the gas-phase intramolecular coupling reaction of CF3 with phenyl via the CF3 migration process of 1 at m/z 273 from iodine to the phenyl to give 3 at m/z 146 could only occur according to an intramolecular aromatic substitution mechanism. Density functional theory (DFT) calculations showed that the gas-phase intramolecular aryltrifluoromethylation of 1 at m/z 273 to 3 at m/z 146 occurred via a Meisenheimer complex intermediate (MC), where the triplevalent I center of 1 was reduced to monovalent I. Most importantly, the structure of 3 at m/z 146 derived from 1 at m/z 273 in ESI-MS/MS process was confirmed by comparison of its MS/MS with that of an authentic PhCF3(•+) at m/z 146 acquired from the electron ionization (EI)-MS/MS analysis of PhCF3. Thus, our studies revealed the intrinsic reactivity tendencies of λ(3)-phenyl(trifluoromethyl)iodonium under solvent-free conditions.

Gas phase decarbonylation and cyclization reactions of protonated N-methyl-N-phenylmethacrylamide and its derivatives via an amide Claisen rearrangement

Gas phase decarbonylation and cyclization reactions of protonated N-methyl-N-phenylmethacrylamide and its derivatives (M·H(+)) were studied by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). MS/MS experiments of M·H(+) showed product ions were formed by loss of CO, which could only occur with an amide Claisen rearrangement. Mechanisms for the gas phase decarbonylation and cyclization reactions were proposed based on the accurate m/z measurements and MS/MS experiments with deuterated compounds. Theoretical computations showed the gas phase Claisen rearrangement was a major driving force for initiating gas phase decarbonylation and cyclization reactions of M·H(+). Finally, the influence of different phenyl substituents on the gas phase Claisen rearrangement was evaluated. Electron-donating groups at the para-position of the phenyl moiety promoted the gas phase Claisen rearrangement to give a high abundance of fragment ions [M - CO + H](+). By contrast, electron-withdrawing groups on the phenyl moiety retarded the Claisen rearrangement, but gave a fragment ion at m/z 175 by loss of neutral radicals of substituents on the phenyl, and a fragment ion at m/z 160 by further loss of a methyl radical.