Structure–enantioselectivity correlation in NHC–Au(I) catalysis for 1,6-enynecyclizations

Hydrogen-Bonded Matched Ion Pair Gold(I) Catalysis

The enantioselective reaction of 1,6-enynes with O-, N-, and C-nucleophiles has been developed by matched ion pair gold(I) catalysis in which the chiral gold(I) cation and anion are H-bonded through a urea group. Very high levels of enantiocontrol are achieved (up to >99:1 er) for a broad scope of substrates. DFT studies demonstrate the importance of the H-bond donor group in anchoring the matched chiral cation- and anion-favoring additional noncovalent interactions.

Indolizy Carbene Ligand. Evaluation of Electronic Properties and Applications in Asymmetric Gold(I) Catalysis

We report herein a new family of carbene ligands based on an indolizine-ylidene (Indolizy) moiety. The corresponding gold(I) complexes are easily obtained from the gold(I)-promoted cyclization of allenylpyridine precursors. Evaluation of the electronic properties by experimental methods and also by DFT calculations confirms strong σ-donating and π-accepting properties of these ligands. Cationization of the gold(I) complexes generates catalytic species that trigger diverse reactions of (poly)unsaturated precursors. When armed with a methylene phosphine oxide moiety on the stereogenic center adjacent to the nitrogen atom, the corresponding bifunctional carbene ligands give rise to highly enantioselective heterocyclizations. DFT calculations brought some rationalization and highlighted the critical roles played by the phosphine oxide group and the tosylate anion in the asymmetric cyclization of γ-allenols.

Studies on gold(I) and gold(III) alcohol functionalised NHC complexes

Five pairs of novel chiral alcohol functionalised gold(i) and gold(iii) NHC complexes derived from chiral amino alcohols, were synthesized and characterised (NMR, IR, HRMS). Single crystal X-ray diffraction data of gold(i) and gold(iii) complexes are reported and discussed. The chiral imidazolium preligands were readily synthesized via the oxalamides, subsequent reduction and final orthoformate condensation. An improved method was used for generation of gold(i) NHC complexes (up to 92%) and further oxidation afforded the corresponding gold(iii) NHC complexes (up to 99%). All the Au(i) and Au(iii) NHC complexes proved far more catalytically active in a 1,6-enyne alkoxycyclization test reaction than our previously tested N,N- and P,N-ligated Au(iii) complexes. Comparative gold(i) and gold(iii) catalytic studies demonstrated different catalytic ability, depending on the NHC ligand flexibility and bulkiness. Excellent yields (92-99%) of target alkoxycyclization product were obtained with both gold(i) and gold(iii) complexes with the bulky N1-Mes-N2-ethanol based NHC ligand.

Enantioselective Alkoxycyclization of 1,6-Enynes with Gold(I)-Cavitands: Total Synthesis of Mafaicheenamine C

Chiral gold(I)-cavitand complexes have been developed for the enantioselective alkoxycyclization of 1,6-enynes. This enantioselective cyclization has been applied for the first total synthesis of carbazole alkaloid (+)-mafaicheenamine C and its enantiomer, establishing its configuration as R. The cavity effect was also evaluated in the cycloisomerization of dienynes. A combination of experiments and theoretical studies demonstrates that the cavity of the gold(I) complexes forces the enynes to adopt constrained conformations, which results in the high observed regio- and stereoselectivities.

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C2 and C1 symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented.

Dataset of asymmetric intramolecular [4+3] cycloaddition reactions catalyzed by NHC-gold(I) complexes

The shared data is the unpublished portion of the experimental section for the article with the title “NHC–Au(I) catalyzed enantioselective intramolecular [4 + 3] cycloaddition of furan propargyl esters”.[1] The preparation of the intermediates for chiral NHC-gold(I) complexes and the furan propargyl ester substrates are included in this article. The ¹H NMR and ¹³C NMR spectra of the gold complexes 17a-19c and the X-ray crystal data of 17a, 18a and cycloaddition product 24 are also provided in this article or in Mendeley Data. Finally, the chiral HPLC spectra used to determine enantiomeric excess and Cartesian coordinates of the optimized structure of 25 and 26 calculated by DFT calculation are also presented in the article.

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

Synthesis and Catalytic Activity of Chiral Dicarbene Dipalladium Complexes Incorporating the S-binaphthol Unit

A series of chiral di-N-heterocyclic carbene (NHC) dipalladium complexes, [{PdPyCl2}2(di-NHC)], in which di-NHC represents a di-imidazolylidene, featuring an (S)-3,3′-dimethyl-2,2′-dimethoxy-1,1′-binaphthalene spacer between the carbene units, have been prepared. The influence of ligand size on the catalytic activity of these complexes in the Suzuki reaction of phenylboronic acid with p-bromotoluene has been investigated. The most sterically hindered complex, bearing the di-isopropylphenyl group, showed the greatest catalytic activity, and it is active for various aryl halides with different electronic and steric properties.