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Synthesis 1989; 1989(10): 735-738
DOI: 10.1055/s-1989-27376
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4-(1,9a-Dihydro-2H-quinolizin-2-ylidene)morpholinium Salts from 4-(1-Methyl-3-phenyl-3-trifluoromethylsulfonyloxy-2-propenylidene)morpholinium Trifluoromethanesulfonate

Fred Krebs* , Gerhard Maas
  • *Fachbereich Chemie, Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-6750 Kaiserslautern, Federal Republic of Germany
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Publication Date:
02 May 2002 (online)

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Treatment of title triflate 1 with two equivalents of pyridine yields the 4-(4-phenyl-1,9a-dihydro-2H-quinolizin-2-ylidene)morpholinium triflate (4). Similarly, quinoline and isoquinoline convert 1 into the benzodi- hydroquinolizine salts 6 and 7, respectively. This novel access to the 1,9a- dihydro-2H-quinolizine system is based on base-initiated cyclization of a dicationic intermediate such as 4-(3-pyridiniopropenylidene) morpholinium ditriflate 2. Tertiary amines catalyze the isomerization of 4 into the 3,4-dihydroquinolizinium triflate 8.