title: 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-4H-chromenes.
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-4H-chromenes. In the EI spectra the hexahydroquinolines undergo the loss of the substituent attached at the C4 position, while the 4H-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 4H-chromenes. The ESI-MS/MS spectra reveal results similar to the EI and CI spectra, since the 4H-chromenes undergo RDA reactions while the hexahydroquinolines form a very stable even-electron pyridium ion derived from the loss of the C4 substituent.
authors.affiliation: Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
authors.forename: N
authors.initials: N
authors.lastname: Martin
authors.forename: R
authors.initials: R
authors.lastname: Martínez-Alvarez
authors.forename: C
authors.initials: C
authors.lastname: Seoane
authors.forename: M
authors.initials: M
authors.lastname: Suárez
authors.forename: E
authors.initials: E
authors.lastname: Salfran
authors.forename: Y
authors.initials: Y
authors.lastname: Verdecia
authors.lastname: Kayali Sayadi N