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Updated: Jul 10, 2026

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Influences on the regioselectivity of palladium-catalyzed allylic alkylations
Uli Kazmaier1, Daniel Stolz, Katja Krämer
1Institut für Organische Chemie, Universität des Saarlandes, Im Stadtwald, Geb. C4.2, 66041 Saarbrücken, Germany. u.kazmaier@mx.uni-saarland.de
Abstract:
Chelated amino acid ester enolates are excellent nucleophiles for palladium-catalyzed allylic alkylations. These enolates react rapidly at -78 degrees C and in general without isomerization of pi-allyl palladium complexes. Therefore, they are good candidates for mechanistic studies and regioselective reactions. Terminal pi-allyl palladium complexes are preferentially attacked at the least hindered position giving rise to linear products, as illustrated with several (E)-configured allylic substrates. Under isomerization free conditions the branched products are formed preferentially from the corresponding (Z)-allyl substrates. An interesting behavior is observed in the reaction of secondary allylic substrates. Aryl-substituted substrates show a significant memory effect which can be explained by an asymmetric pi-allyl complex. For alkyl-substituted substrates a strong dependence of the regioselectivity on the leaving group is observed, which can be explained by different conformations in the ionization step. Under isomerization free conditions the product ratio gives important information about this step.
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