Gas Phase Decarbonylation and Cyclization Reactions of Protonated N-Methyl-N-Phenylmethacrylamide and Its Derivatives Via an Amide Claisen Rearrangement

Abstract

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.

Gas-phase fluorine migration reactions in the radical cations of pentafluorosulfanylbenzene (Aryl―SF5) and benzenesulfonyl fluoride (Aryl―SO2F) derivatives and in the 2,5-xylylfluoroiodonium ion

“…Most of these gas‐phase F‐atom migration reactions of aromatic fluorinated compounds have the common aromatic substitution mechanism. We have previously studied some kinds of these gas‐phase reactions, such as Smiles rearrangements, sulfonyl–sulfinate rearrangements, and Claisen rearrangement …”

Two competing ionization processes in ESI-MS analysis of N-(1,3-diphenylallyl)benzenamines: formation of the unusual [M−H]+ ion versus the regular [M+H]+ ion

“…Analysis of Table 2 reveals that the positive charge is mainly located on the N16 and C17 atoms in the [MþH] þ ion. Relative to [MþH] þ , there is much more charge on the C6 (A-ring) and the C22 (C-ring) atoms, and less charge on the N16 and C17 atoms in [MÀH] þ by comparing the boldface values in Table 2, indicating that the positive charge can be delocalized over the The subsequent cyclization of I-193 via intramolecular nucleophilic reaction 24,31,32 occurs to give an isomeric ion I-193 b, which undergoes further fragmentation to produce the ion at m/z 115 by losing benzene. Whereas, elimination of aniline does not occur easily in fragmentation of [1ÀH] þ via the breakage of the double bond C9 ¼ N16.…”

N"-[(3Z)-1-Acetyl-5-chloro-2-oxo-1,2-dihydro-3H-indol-3-ylidene]thiocarbonohydrazide

“…Further fragmentation of the ion at m/z 236 in MS 3 led to two main fragments at m/z 194 and 166 followed by their corresponding isotopic peaks. The peak at m/z 194 is due to a loss of an acetyl group, and the peak at 166 to a further loss of CO, which occurs in amides as Claisen rearrangement [25].…”