Counterion effects in iminium-activated electrophilic aromatic substitutions of pyrroles.
Electrophilic substitution of pyrroles by α,β-unsaturated iminium ions is slow in acetonitrile when only weakly basic counterions are present. When the reactions are carried out in the presence of KCF(3)CO(2), fast deprotonation of the intermediate σ-adducts occurs, and the rate constant for the rate-determining CC bond-forming step can be predicted from the electrophilicity parameter E of the iminium ion and the N and s parameters of the pyrroles.
Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13 (Haus F), 81377 München, Germany.
Sami
S
Lakhdar
Herbert
H
Mayr