A cooperative N-heterocyclic carbene/palladium catalysis system

Abstract

N-heterocyclic carbenes (NHC) have been extensively studied as organocatalysts and ligands for transition metals, but the successful integration of NHCs and late transition metals in cooperative catalysis remains an underexplored area. We have developed a cooperative palladium-catalyzed allylation of NHC-activated aldehydes to access a variety of 3-allyl dihydrocoumarin derivatives. Kinetic experiments support a cooperative pathway for this transformation.

Recent advances in employing homoenolates generated by N-heterocyclic carbene (NHC) catalysis in carbon–carbon bond-forming reactions

“…The competing pathway of homoenolate [3+2] annulation to produce g-lactones was suppressed by introducing an equimolar quantity of a protic acid additive (acetic acid) to the combination of triazolium precatalyst 32 and an acetate base in the reaction. 40 39 A proof of concept process that proceeds via cooperative catalysis involving NHC and a palladium catalyst was developed by Scheidt in 2014.…”

Synergistic N‐Heterocyclic Carbene/Palladium‐Catalyzed Reactions of Aldehyde Acyl Anions with either Diarylmethyl or Allylic Carbonates

“…3-Methylbutanal also served as as uitable substrate (3ca). [8,9] Aromatic aldehydes did not participate in the reaction (data not shown). Functional groups such as alkene and thiomethyl substituents at the terminus of the aliphatic chain aldehyde substrates were tolerated (3fa, 3ga).…”

Kooperative Katalyse mit N‐heterocyclischen Carbenen

“…Die Gruppen von Hamada, [73] Glorius [74] und She [75] zeigten, dass NHC-und Pd-Katalyse miteinander kompatibel sind. [77] Um zu vermeiden, dass der Katalysator unwirksam wird, stellten wir die Hypothese auf,d ass die Anwesenheit eines zusätzlichen zweizähnigen Liganden eine irreversible Pd-NHC-Bindung verhindern kann. Das erste Beispiel einer kooperativen Aktivierung stammt von Liu und Mitarbeitern.…”