| Abstract: | 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. |
