Stereospecific fragmentation processes in cycloalkane/cycloalkene-fused isomers of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives

K. Pihlaja, V. V. Ovcharenko, G. Stájer

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10 Citations (Scopus)

Abstract

Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M ions. The observed 90% stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e.g., in the formation of [M - C 3H 5O] + ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.

Original languageEnglish
Pages (from-to)393-401
Number of pages9
JournalJournal of the American Society for Mass Spectrometry
Volume10
Issue number5
DOIs
Publication statusPublished - 1999

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Cycloparaffins
Isomers
Ions
Derivatives
X-Ray Diffraction
Ionization
Electrons
Conformations
Substitution reactions
Nuclear magnetic resonance
Decomposition
X ray diffraction

ASJC Scopus subject areas

  • Structural Biology
  • Spectroscopy

Cite this

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title = "Stereospecific fragmentation processes in cycloalkane/cycloalkene-fused isomers of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives",
abstract = "Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M +· ions. The observed 90{\%} stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e.g., in the formation of [M - C 3H 5O] + ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M +· ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.",
author = "K. Pihlaja and Ovcharenko, {V. V.} and G. St{\'a}jer",
year = "1999",
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T1 - Stereospecific fragmentation processes in cycloalkane/cycloalkene-fused isomers of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives

AU - Pihlaja, K.

AU - Ovcharenko, V. V.

AU - Stájer, G.

PY - 1999

Y1 - 1999

N2 - Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M +· ions. The observed 90% stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e.g., in the formation of [M - C 3H 5O] + ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M +· ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.

AB - Electron ionization-induced fragmentations were studied in a set of saturated pyrrolo[2,1-b][1,3]oxazin-6-one derivatives fused to either cycloalkane or cycloalkene rings, including seven pairs of cis/trans and endo/exo annelation isomers. Fragmentation patterns were confirmed by accurate mass measurements and metastable ion spectra. A number of striking differences were observed between the mass spectra of cyclohexene-fused isomers due to highly stereospecific retro-Diels-Alder (RDA) fragmentation of their M +· ions. The observed 90% stereospecificity is abnormally high in the light of the recent classification (A. Mandelbaum, 1994) of stereospecific RDA fragmentations according to the degree of substitution of the cyclohexene ring being cleaved. In the absence of RDA processes, the differences between the mass spectra of cyclohexane-fused isomers originated from heterocyclic fragmentations. The assumed mechanistic interpretation of the observed differences, e.g., in the formation of [M - C 3H 5O] + ions, was consistent with the condensed-state conformations of these isomers determined previously by NMR and X-ray diffraction studies. Because of rapid RDA decompositions of their rather unstable M +· ions, the spectra of the diendo/diexo norbornene-fused isomers were virtually identical.

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