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Synlett 1992; 1992(6): 524-526
DOI: 10.1055/s-1992-21402
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Spiroanellated 1-Cyclopropyldihydro-2-azaazulenes: Cyclopropylimine Rearrangement to Cyclohepta [a] pyrrolizines1

Karsten Giller* , Mark S. Baird, Armin de Meijere
  • *Institut für Organische Chemie, Universität Hamburg, Martin-Luther-King-Platz 6, D-2000 Hamburg 13, Germany
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Publication Date:
08 March 2002 (online)

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Methyl 2-chloro-2-[1-(α-cyclopropylbenzylideneamino)-cyclopropyl]acetates 3 cyclize to spirocyclopropane-anellated 1-cyclopropyl-2-azaazulenes 4 upon α-dehydrohalogenation with potassium tert-butoxide. The cyclopropylimine moiety can be rearranged by nucelophilic attack of iodide and subsequent borohydride reduction of the resulting iminium-eneammonium salts to give methyl 1,2,3,5,5a,10b-hexahydrospiro [cyclohepta-[a]pyrrolizine-5,1′-cyclopropane]-5a-carboxylates 9 in good yields. This method is applicable to 1-cyclopropyl-3,4-dihydroisoquinoline 10 yielding two diastereomeric 1,2,3,5,6,10b-hexahydro-5-(1′-methoxycarbonylethenyl)-1-methylpyrrolo[2,1-a]isoquinolines cis-and trans-13.