Claisen rearrangement induced by low‐energy collision of ESI‐generated, protonated benzyloxy indoles

Abstract

The Claisen rearrangement is a well-known process occurring in condensed phase. In the gas-phase protonated allyl phenyl ethers, propargyl phenyl ethers, and N-allyl aniline produced by positive ion chemical ionization undergo Claisen rearrangement. This reaction has been observed even in the case of odd-electron molecular ions. Phenyl allenyl ether molecular ions actually undergo Claisen rearrangement, producing intense [M - CO](+*) ions. In this investigation, the behavior of protonated benzyloxy indole and some of its derivatives, obtained in electrospray conditions, is described. Low-energy MS/MS experiments carried out on [M + H](+) species show CO loss and an unexpected water loss: both can be justified only by the occurrence of Claisen rearrangement. Deuterium labeling experiments confirm this mechanism. The influence of different substituents in the indole moiety is discussed.

Protonation of curcumin triggers sequential double cyclization in the gas-phase: An electrospray mass spectrometry and DFT study

“…Electrospray ionization (ESI) generates protonated/deprotonated molecules and introduces them to the gas-phase. The unimolecular transformations of both [M + H] + and [M − H] − ions and the mechanism of these reactions have been studied by various experimental approaches, including tandem mass spectrometry and DFT calculations In fact, acidcatalyzed transformations of organic molecules in solution can be predicted on the basis of mass spectrometric fragmentations of protonated molecules [22,23]. The use of mass spectrometer for studying various chemical reactions has led to the suggestion that it is "complete chemical laboratory" [24].…”

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

“…Gas phase Claisen rearrangements of protonated allyl phenyl ethers [26], protonated Nallylaniline [27], and protonated benzyloxy indoles have been investigated by mass spectrometry [28]. Similar gas phase Claisen rearrangement reactions have been reported in the dissociation process of radical cations formed by electron ionization mass spectrometry (EI-MS) [29][30][31][32][33].…”

Explanation through density functional theory of the unanticipated loss of CO2and differences in mass fragmentation profiles of ritonavir and its rCYP3A4-mediated metabolites

“…Also, several reports were found, which mentioned of unusual neutral losses like SO, SO 2 , H 2 SO 2 , CO, H 2 O, NH 3 , etc . from the central part of protonated or deprotonated ions . Many of these investigations also proposed mechanisms of occurrence of such unusual losses.…”

“…Many of these investigations also proposed mechanisms of occurrence of such unusual losses. In most studies involving loss of SO, SO 2 , H 2 SO 2 , CO and H 2 O, the proposition was a gaseous phase rearrangement, which was hypothesized to be energetically favoured . The elimination of NH 3 was justified through an ion–neutral complex formation …”