An Original L‐shape, Tunable N‐Heterocyclic Carbene Platform for Efficient Gold(I) Catalysis

Abstract

The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C−N, C−O, and C−C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic AuI active species by ligand 1Me.

Gold(I) Complexes with Eight‐Membered NHC Ligands: Synthesis, Structures and Catalytic Activity

“…Gold complexes are excellent catalysts for the cyclization of a variety of enynes . This divergent transformation has been examined in the presence of phosphine‐, phosphite‐ and NHC‐based catalysts due to the growing applicability in the synthesis of complex molecules …”

N‐Heterocyclic Carbenes as Key Intermediates in the Synthesis of Fused, Mesoionic, Tricyclic Heterocycles

“…Reacting bromo derivative 1 with the potassium salt of the dimethyl malonate anion under milder conditions, that is, at room temperature, allowed the isolation of zwitterionic compound 3 , in which the malonate unit is grafted onto the 5‐position of the cationic heterobicycle. The C−C bond formation between the two parts occurred through an SN Ar pathway, as we reported previously for related nucleophiles . Two equivalents of the potassium malonate reagent were required in this case because the second equivalent served as a base to trap the acidic proton on the central malonate carbon atom in the intermediate after the SN Ar reaction.…”

“…We recently reported on 5‐functionalized imidazo[1,5‐ a ]pyridin‐3‐ylidene (IPy) ligands, the precursors of which were efficiently accessed through a key nucleophilic aromatic substitution (SN Ar ) on the 5‐bromoimidazo[1,5‐ a ]pyridinium cation ( A⋅ H) + (Scheme E) . Although the pre‐carbenic imidazolium ring was unaffected, we speculated on the possibility to access, at least transiently, the corresponding carbene A (or an analogue), and thus, to generate a formal 1,3‐dipole composed of the nucleophilic carbenic center and the electrophilic bromosubstituted pyridinic position.…”

An Original L‐shape, Tunable N‐Heterocyclic Carbene Platform for Efficient Gold(I) Catalysis

“…Thebarbituric heterocycle was chosen as it combines urea and malonate units into its structure,which actually may serve for further derivatization or during catalysis. [15] Theanionic gold(I) complex [AuCl(1)]Li ([4]Li)was then cleanly obtained by reacting the stable free NHC [1]Li with AuCl(tht) at low temperature. [12] Compound 1·H was fully characterized by spectroscopic and analytical techniques and its molecular structure was firmly established by single crystal X-Ray diffraction (XRD) (Figure 2).…”