59. “The Synthesis and Protonation of 1,1-Di(1-pyrrolyl)alkenes”
    Schärer, J.-C.; Etienne, R.; Burger, U.
    Helv. Chim. Acta 1985, 68, 2282-2286.

It is shown that lithiation of di(1-pyrrolyl)methane (3) can be directed either towards the C(α) ring positions or to the central CH₂ group, depending upon the solvent and the complexing agents chosen. Di(1-pyrrolyl)-methyllithium (6), resulting from CH₂ deprotonation, is intercepted by aldehydes and converted to the title alkenes in a few straightforward steps. Protonation of 1,1-di(1-pyrrolyl)ethylene (10) is found to occur under kinetic control at the terminal olefinic position. In HBF₄. Me₂O the resulting 5-azionafulvene-type ion 14 can be observed by low-temperature NMR spectroscopy. In FSO₃H, however, protonation is directed under thermodynamic control to both pyrrole rings. The resulting symmetrical dication 13 persists even at room temperature.

DOI : 10.1002/hlca.19850680823 

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