VALENCE ISOMERS OF AROMATIC SYSTEMS - SYNTHESIS OF PYRROLO-3-AZABENZVALENE

Valence Isomers of Aromatic Systems. The Synthesis of Pyrrolo‐3‐azabenzvalene 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. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim