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An overview of the retro‐Diels‐Alder reaction in semiunsaturated heterocyclic rings: mass spectra of new substituted 1,4,5,6,7,8‐hexahydroquinolines and their oxo‐analogues 5,6,7,8‐tetrahydro‐4 H ‐chromenes
Author(s) -
Martin N.,
MartínezAlvarez R.,
Seoane C.,
Suárez M.,
Salfran E.,
Verdecia Y.,
Kayali Sayadi N.
Publication year - 2000
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/1097-0231(20010115)15:1<20::aid-rcm189>3.0.co;2-b
Subject(s) - chemistry , substituent , electrospray ionization , mass spectrum , electron ionization , ionization , mass spectrometry , tandem mass spectrometry , medicinal chemistry , chemical ionization , ion , computational chemistry , organic chemistry , chromatography
Abstract Electron impact ionization (EI), chemical ionization (CI), electrospray ionization (ESI) and tandem mass spectrometry (MS/MS) were used to investigate a number of relatively large and structurally related new heterocycles such as substituted 1,4,5,6,7,8‐hexahydroquinolines and their oxa‐analogues 5,6,7,8‐tetrahydro‐4 H ‐chromenes. In the EI spectra the hexahydroquinolines undergo the loss of the substituent attached at the C4 position, while the 4 H ‐chromenes undergo a retro‐Diels‐Alder reaction (RDA) after elimination of the C4 substituent. Under chemical ionization conditions the RDA reaction is observed only for the 4 H ‐chromenes. The ESI‐MS/MS spectra reveal results similar to the EI and CI spectra, since the 4 H ‐chromenes undergo RDA reactions while the hexahydroquinolines form a very stable even‐electron pyridium ion derived from the loss of the C4 substituent. Copyright © 2001 John Wiley & Sons, Ltd.