Electron Impact Induced Loss of C-5/C-8 Substituents of 1,2,3,4-Tetrahydroisoquinolines, V: Synthesis and Mass Spectrometric Fragmentation of Dihydroisoindole Derivatives
✍ Scribed by Frank Knefeli; Klaus K. Mayer; Wolfgang Wiegrebe
- Publisher
- John Wiley and Sons
- Year
- 1989
- Tongue
- English
- Weight
- 696 KB
- Volume
- 322
- Category
- Article
- ISSN
- 0365-6233
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✦ Synopsis
C-8-substituted N-methyl-l,2,3,4-tetrahydroisoquinoline radical cations lose the complete substituent in a one step reactlion giving rise to an unexpected ion at m/z 146, which is probably identical with the dihydroisoindolylmethylcation A. The dihydroisoindoles 1. 10, and 16 were prepared as potentially alternative precursors of ion A. However, the ion at m/z 146 in their EI mass spectra is of very low intensity, so CIDexperiments for smciural comparison could not be performed. The electron impact induced fragmentations of 1.10, and 16 arr discussed.
ElektronenstoR-induzierter
Verlust der Substituenten an C-5 und C-8 bei 1,2,3,4TetrahydroisochinoIinen, 5. Mitt.: Synthese und massenspktrometrische Fragmentierungen von Dihydroisoindol-Derivaten An C-8 substituierte N-Methyl-l,2,3,4-tetrahydroisochinolin-Radikalkationen verlieren den gesamten Substituenten in einstufiger Reaktion unter Bildung eines unerwarteten Ions bei d z 146, dessen postulierte Identit% mit dern Dihydroisoindolylmthyl-Kation A gepriift weden sollte. Die Dihydroisoindole 1,lO und 16mzigliche Vorlaufer von Awurden synthetisierk In ihren EI-MS tritt das Ion bei m/z 146 rnit nur sehr geringer Intensit;it auf, CIDMessungen zum Strukturvergleich konnten daher nicht durchgefii werden. Die ElektronenstoO-induzie-n Fragmentierungen von 1.10 und 16 werden diskutiert.
N-Methyl-1,2,3,4-tetrahydroisoqlllinolines substituted at C-5 and/or C-8 lose these substituents upon electron impact (EI) induced ionization forming fragment ions of high intensity which correspond to a formally "simple" cleavage of the Ck-X-bond. If X is a carbon chain these ions can be more prominent than ions resulting from benzylic cleavage').
This unexpected behaviour points towards functional group interaction in the M+. prior to bond breaking, an assumption supported by the fact that the percentage of the total ion current corresponding to the (M-X)+-ions is increased by reducing the electron energy from 70 eV to 10 eV. These results are typical of rearrangements preceding fragmentation and are in contrast to simple bond Therefore, we proposed that dihydroisoinde lylmethyl cations might be formed from C-%substituted Nmethyl-1,2,3,4-tetrahydroisoquinolines under EI conditions (Scheme 1):
In order to verify this hypothesis by CID-MIKES') we synthesized C-4-substituted dihydroisoindoline derivatives as precursors which are expected to form ion A by a favoured cleavage after EI. Here we describe the synthesis of some pertinent molecules. Scheme 1 1) 4-(N-Benzoyl-aminomethyl)-Z,3-dihydro-2-methylla-isoindole (1) This compound is supposed to form ion A by benzylic cleavage (Scheme 2): +) Collision Induced Dissociation -Mass Analyzed Ion Kinetic Energy Spectroscopy3).