31. “Valenzisomere aromatischer systeme. Die Synthese des Pyrrolo-3-azabenzvalens”
    Burger, U.; Dreier, F.
    Helv. Chim. Acta 1979, 62, 540-545.

4-Azapentalenyl anion (4) is shown to react with dichloromethane/butyl lithium in two fundamentally different ways depending on whether diethyl ether or tetrahydrofuran is chosen as solvent. In the first case a tetracyclic valence isomer of indolizine, i.e. pyrrolo-3-azabenzvalene (6) is formed together with indolizine (8) itself. In THF however, a pyrrylbutenyne (9), isomeric with the products mentioned above is obtained in a stereospecific reaction. Once again the appearance of indolizine (8) accompanies the reaction. Mechanistic implications, based on the finding that the heterovalene 6 is not a precursor of the pyrrylbutenyne 9, are discussed.

DOI : 10.1002/hlca.19790620222 

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