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The Synthesis and Protonation of 1,1‐Di(1‐pyrrolyl)alkenes
Author(s) -
Schärer JeanClaude,
Etienne Robert,
Burger Ulrich
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680823
Subject(s) - chemistry , protonation , deprotonation , dication , methyllithium , pyrrole , ring (chemistry) , solvent , medicinal chemistry , nuclear magnetic resonance spectroscopy , photochemistry , stereochemistry , ion , organic chemistry
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 CH 2 group, depending upon the solvent and the complexing agents chosen. Di(1‐pyrrolyl)‐methyllithium ( 6 ), resulting from CH 2 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 HBF 4 . Me 2 O the resulting 5‐azionafulvene‐type ion 14 can be observed by low‐temperature NMR spectroscopy. In FSO 3 H, however, protonation is directed under thermodynamic control to both pyrrole rings. The resulting symmetrical dication 13 persists even at room temperature.