The Stabilizing Effects in Gold Carbene Complexes

Oxidation States: Intrinsically Ambiguous?

The oxidation state ( OS ) formalism is a much-appreciated good in chemistry, receiving wide application. However, like all formalisms, limitations are inescapable, some of which have been recently explored. Providing a broader context, we discuss the OS and its interpretation from a computational perspective for transition metal (TM) complexes. We define a broadly applicable and easy-to-use procedure to derive OS s based on quantum chemical calculations, via the use of localized orbitals, dubbed the Intrinsic OS . Applying this approach to a cobalt complex in five OS s, isolated by Hunter and co-workers (Inorg. Chem.2021, 60, 17445), we find that the calculated Intrinsic OS matches the formal OS , consistent with the experimental characterization. Through analysis of the delocalized orbitals, the ligand field of the Co(III) complex is found to be "inverted", despite every cobalt-ligand bond being classically dative from the localized perspective-a bonding scenario very similar to that of [Cu(CF3)4]-. This is not atypical but rather a natural consequence of these metals bonding in the high-valent region, and we propose a more restrictive definition of (locally) inverted bonding. Additionally, two bonding descriptors within the Intrinsic Bonding Orbital (IBO) framework (σ-gain and π-loss) are introduced, which enable facile quantification of electron-sharing covalency across a broad range of TM complexes.

Tf2O-mediated [4+2]-annulation of anthranils with 2-chloropyridines: enabling access to pyridoquinazolinones and euxylophoricine B

We present an efficient approach for synthesizing pyridoquinazolinones in the presence of triflic anhydride utilizing anthranils and 2-chloropyridines as starting materials. In this process, Tf2O initially activates anthranils forming an electrophilic 1-((trifluoromethyl)sulfonyl)benzo[c]isoxazol-1-ium species. This species undergoes an in situ annulation reaction with 2-chloropyridines, resulting in therapeutically useful pyridoquinazolinones. The reaction is tolerant to various functional groups, allowing access to a wide range of substituted pyridoquinazolinones in good yields. Furthermore, the synthesis of euxylophoricine B, known to be an antitumor agent, was also achieved.

Facile synthesis and bonding of 4-ferrocenyl-1,2,4-triazol-5-ylidene complexes

Ferrocene-substituted carbenes have emerged as attractive, redox-active ligands. However, among the compounds studied to date, ferrocenylated 1,2,4-triazol-5-ylidenes, which are closely related to the archetypal imidazol-2-ylidenes, are still unknown. Here, we demonstrate that the triazolium salt [CHN(Me)NCHN(Fc)]I (2; Fc = ferrocenyl), obtained by alkylation of 4-ferrocenyl-4H-1,2,4-triazole (1) with MeI, reacts selectively with metal alkoxide/hydroxide precursors [(cod)Rh(OMe)]2 and [(IPr)Au(OH)] (cod = cycloocta-1,5-diene, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to produce the ferrocene-substituted 1,2,4-triazol-5-ylidene complexes [(cod)RhI{CN(Me)NCHN(Fc)}] and [(IPr)Au{CN(Me)NCHN(Fc)}]I in good yields. The complexes were characterised by NMR and IR spectroscopy, mass spectrometry, cyclic voltammetry, and single-crystal X-ray diffraction analysis. Density function theory (DFT) calculations were used to rationalise the electrochemical behaviour of the carbene complexes and to elucidate the bonding situation in these compounds. An analysis using intrinsic bond orbitals (IBOs) revealed that the 1,2,4-triazol-5-ylidene ligand exerted a strong trans influence and showed a synergistic stabilisation by the negative inductive and positive π-donor effects of the nitrogen atoms adjacent to the carbene carbon atom; these effects were enhanced by conjugation with the CHN bond at the exterior, similar to that in imidazol-2-ylidenes.

1,2-Silyl Rearrangement in Gold Carbene Chemistry: Synthesis of Furyl-Decorated Tetrasubstituted Silylallene Derivatives

The gold-catalyzed reaction of 2-en-4-ynones with alkynylsilanes provides fully substituted allene derivatives bearing furyl and silyl groups. This transformation would involve generation of a gold furyl carbene intermediate, which regioselectively undergoes a nucleophilic attack by the alkynylsilane at the electrophilic carbene carbon atom with the formation of a β-gold vinyl cation species. The subsequent release of the gold catalyst, accompanied by a 1,2-silyl shift, leads to the formation of tetrasubstituted allene products.

Dinuclear gold(I) complexes based on carbene and diphosphane ligands: bis[2-(dicyclohexylphosphano)ethyl]amine complex inhibits the proteasome activity, decreases stem cell markers and spheroid viability in lung cancer cells

Three new dinuclear gold(I) complexes (1-3) containing a carbene (1,3-Bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr)) and diphosphane ligands [bis(1,2-diphenylphosphano)ethane (Dppe), bis(1,3-diphenylphosphano)propane (Dppp) and bis[2-(dicyclohexylphosphano)ethyl]amine (DCyPA)], were synthesized and characterized by elemental analysis and, ESI-MS, mid FT-IR and NMR spectroscopic methods. The structures of complexes 2 and 3 were determined by X-ray crystallography, which revealed that the complexes are dinuclear having gold(I) ions linearly coordinated. The anticancer activities of the complexes (1-3) were evaluated in lung (A549), breast (MC-F7), prostate (PC-3), osteosarcoma (MG-63) and ovarian (A2780 and A2780cis) cancer models. Growth inhibition by the new complexes was higher than cisplatin in all cell lines tested. The mechanism of action of complex 3 was investigated in A549 cells using 2-dimensional (2D) models and 3D-multicellular tumor spheroids. Treatment of A549 cells with complex 3 caused: the induction of apoptosis and the generation of reactive oxygen species; the cell cycle arrest in the G0/G1 phase; the inhibition of both the proteasome and the NF-kB activity; the down-regulation of lung cancer stem cell markers (NOTCH1, CD133, ALDH1 and CD44). Complex 3 was more active than cisplatin also in 3D models of A549 lung cancer cells.

Revisiting sp2 Dilithio Methandiides: From Geometric Curiosity to Simple Bonding Description

The reported tetracoordinate dilithio methandiide complex from Liddle and co-workers (1) is investigated from a coordination chemistry perspective, to probe the origin of its intriguing geometry. Through the application of a variety of computational techniques, non-covalent (steric, electrostatic) interactions are found to be dominant. Further, we arrive at a bonding description which emphasizes the tricoordinate sp2 -hybridized nature of the central methandiide carbon, differing somewhat from the original proposal. Thus, 1 is distinct from other dilithio methandiides since it contains only one C-Li σ-bond, and is found to be comparable to a simple aryllithium compound, phenyllithium.

Bond-Dissociation Energies to Probe Pyridine Electronic Effects on Organogold(III) Complexes: From Methodological Developments to Application in π-Backdonation Investigation and Catalysis

In this work, we report on the synthesis of several organogold(III) complexes based on 4,4'-diterbutylbiphenyl (C^C) and 2,6-bis(4-terbutylphenyl)pyridine (C^N^C) ligands and bond with variously substituted pyridine ligands (pyrR). Altogether, 33 complexes have been prepared and studied with mass spectrometry using higher-energy collision dissociation (HCD) in an Orbitrap mass spectrometer. A complete methodology including the kinetic modeling of the dissociation process based on the Rice-Ramsperger-Kassel-Marcus (RRKM) statistical method is proposed to obtain critical energies E0 of the pyrR loss for all complexes. The capacity of these E0 values to describe the pyridine ligand effect is further explored, at the same time as more classical descriptors such as 1H pyridinic NMR shift variation upon coordination and Au-NpyrR bond length measured by X-ray diffraction. An extensive theoretical work, including density functional theory (DFT) and domain-based local pair natural orbital coupled-cluster theory (DLPNO-CCSD(T)) methods, is also carried out to provide bond-dissociation energies, which are compared to experimental results. Results show that dissociation energy outperforms other descriptors, in particular to describe ligand effects over a large electronic effect range as seen by confronting the results to the pyrR pKa values. Further insights into the Au-NpyrR bond are obtained through an energy decomposition analysis (EDA) study, which confirms the isolobal character of Au+ with H+. Finally, the correlation between the lability of the pyridine ligands toward the catalytic efficiency of the complexes could be demonstrated in an intramolecular hydroarylation reaction of alkyne. The results were rationalized considering both pre-catalyst activation and catalyst reactivity. This study establishes the possibility of correlating dissociation energy, which is a gas-phase descriptor, with condensed-phase parameters such as catalysis efficiency. It therefore holds great potential for inorganic and organometallic chemistry by opening a convenient and easy way to evaluate the electronic influence of a ligand toward a metallic center.

Combining ligand-enhanced backdonation and steric shielding to stabilize a mono-substituted Au(I) carbene

A mono-substituted Au(I) carbene was prepared by reacting HC(N₂)(Dmp) (Dmp = 2,6-dimesitylphenyl) with an (o-carboranyl)-diphosphine AuNTf₂ complex. It is stable up to -10 °C and was characterized by NMR spectrocopy. According to DFT calculations, the chelating P^P ligand enhances Au → C_carb backdonation, while the Dmp substituent provides kinetic stabilization but does not bias the electronic structure of the carbene complex.

Advancements in Gold-Catalyzed Cascade Reactions to Access Carbocycles and Heterocycles: An Overview

This review summarizes recent developments (from 2006 to 2022) in numerous important and efficient carbo- and heterocycle generations using gold-catalyzed cascade protocols. Herein, methodologies involve selectivity, cost-effectiveness, and ease of product formation being controlled by the ligand as well as the counter anion, catalyst, substrate, and reaction conditions. Gold-catalyzed cascade reactions covered different strategies through the compilation of various approaches such as cyclization, hydroarylation, intermolecular and intramolecular cascade reactions, etc. This entitled reaction is also useful for the synthesis of spiro, fused, bridged carbo- and heterocycles.

Spectroscopic Manifestations and Implications for Catalysis of Quasi-d10 Configurations in Formal Gold(III) Complexes

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand σ-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal Cu^III complex [Cu(CF₃ )₄ ]^1- , in which the metal center tries to populate its formally unoccupied 3d_x2-y2 orbital via σ-bonding, leading to a reduced d¹⁰ Cu^I description. However, Au L₃ -edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the Au^III species is still possible, showing that a genuine d¹⁰ configuration is not achieved. We also find an increased electron-sharing nature of the σ-bonds in the Au^I species, relative to their Ag^I and Cu^I analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5d_x2-y2 or 6s orbital, respectively, in bonding, indicating why Au^I and Au^III complexes often have similar reactivity.

How reduced are nucleophilic gold complexes?

Nucleophilic formal gold(-I) and gold(I) complexes are investigated via Intrinsic Bond Orbital analysis and Energy Decomposition Analysis, based on density functional theory calculations. The results indicate gold(0) centres engaging in electron-sharing bonding with Al- and B- based ligands. Multiconfigurational (CASSCF) calculations corroborate the findings, highlighting the gap between the electonic structures and the oxidation state formalism.

Umpolung in a Pair of Cobalt(III) Terminal Imido/Imidyl Complexes

Reaction of the Co^I complex [(TIMMN^mes)Co^I](PF₆) (1) (TIMMN^mes=tris‐[2‐(3‐mesityl‐imidazolin‐2‐ylidene)‐methyl]amine) with mesityl azide yields the Co^III imide [(TIMMN^mes)Co^III(NMes)](PF₆) (2). Oxidation of 2 with [FeCp₂](PF₆) provides access to a rare Co^III imidyl [(TIMMN^mes)Co(NMes)](PF₆)₂ (3). Single‐crystal X‐ray diffractometry and EPR spectroscopy confirm the molecular structure of 3 and its S=1/2 ground state. ENDOR, X‐ray absorption spectroscopy and computational analyses indicate a ligand‐based oxidation; thus, an imidyl‐radical electronic structure for 3. Migratory insertion of one ancillary NHC to the imido ligand in 2 gives the Co^IN‐heterocyclic imine (4) within 12 h. Conversely, it takes merely 0.5 h for 3 to transform to the Co^II congener (5). The migratory insertion in 2 occurs via a nucleophilic attack of the imido ligand at the NHC to give 4, whereas in 3, a nucleophilic attack of the NHC at the electrophilic imidyl ligand yields 5. The reactivity shunt upon oxidation of 2 to 3 confirms an umpolung of the imido ligand.

Gold(I) α-Trifluoromethyl Carbenes: Synthesis, Characterization and Reactivity Studies

Aryl trifluoromethyl diazomethanes 2-R (R=Ph, OMe, CF3 ) are readily decomposed by the (o-carboranyl)diphosphine gold(I) complex 1. The resulting α-CF3 substituted carbene complexes 3-R have been characterized by multi-nuclear NMR spectroscopy as well as X-ray crystallography (for 3-Ph). The bonding situation was thoroughly assessed by computational means, showing stabilization of the electrophilic carbene center by π-donation from the aryl substituent and backdonation from Au, as enhanced by the chelating P^P ligand. Reactivity studies under stoichiometric and catalytic conditions substantiate typical carbene-type behavior for 3-Ph.

Dichotomy of platinum(II) and gold(III) carbene intermediates switching from N- to O-selectivity

Pt(II) and Au(III)-mediated intermolecular divergent annulations of benzofurazans and ynamides highlighted the N- to O-selectivity of tunable metal carbene intermediates. PtCl₂ with a bulky phosphite ligand resulted in the specific synthesis of six-membered quinoxaline N-oxides and successfully suppressed the in-situ deoxygenation of N-oxides. On the other hand, an unique gold(III) catalyst (2,6-di-MeO-PyrAuCl₃) led to the five-membered ring products, benzimidazoles. A broad scope of functional groups was well compatible, delivering better yields and selectivities in contrast to conventional gold(I) catalysts. The different behavior of presumed platinum(II) and gold(III) carbenes with respect to chemoselectivity was intensively examined by experiments and DFT calculations. A detailed mechanistic study, based on DFT calculations, revealed that the highly electrophilic carbocation-like gold(III) carbene triggers an oxophilic cyclization, followed by a cascade ring contraction and acyl migration. On the contrary, the Pt carbene species is less cationic, favoring the formation of the six-membered ring via N-attack.

Benzofurazan, a cyclic heterocycle, can form open-chain metal carbene species in the presence of suitable catalysts. Here the authors show divergent reactivity when using gold(III) and platinum(II) catalysts, and perform computational and experimental mechanistic studies to explain the differing reactivity

Access to Indole-Fused Benzannulated Medium-Sized Rings through a Gold(I)-Catalyzed Cascade Cyclization of Azido-Alkynes

Because benzannulated and indole-fused medium-sized rings are found in many bioactive compounds, combining these fragments might lead to unexplored areas of biologically relevant and uncovered chemical space. Herein is shown that α-imino gold carbene chemistry can play an important role in solving the difficulty in the formation of medium-sized rings. Namely, phenylene-tethered azido-alkynes undergo arylative cyclization through the formation of a gold carbene intermediate to afford benzannulated indole-fused medium-sized tetracycles. The reactions allow a range of different aryl substitution patterns and efficient access to these otherwise difficult-to-obtain medium-sized rings. This study also demonstrates the feasibility of the semihollow-shaped C-dtbm ligand for the construction of a nine-membered ring.

Azido-Alkynes in Gold(I)-Catalyzed Indole Syntheses

The exploitation of nitrogen-functionalized reactive intermediates plays an important role in the synthesis of biologically relevant scaffolds in the field of pharmaceutical sciences. Those based on gold carbenes carry a strong potential for the design of highly efficient cascade processes toward the synthesis of compounds containing a fused indole core structure. This personal account gives a detailed explanation of our contribution to this sector, and embraces the reaction development of efficient gold-catalyzed cascade processes based on diversely functionalized azido-alkynes. Challenging cyclizations and their subsequent application in the synthesis of pharmaceutically relevant scaffolds and natural products conducted in an intra- or intermolecular fashion are key features of our research.

Main Avenues in Gold Coordination Chemistry

In this contribution, we provide an overview of the main avenues that have emerged in gold coordination chemistry during the last years. The unique properties of gold have motivated research in gold chemistry, and especially regarding the properties and applications of gold compounds in catalysis, medicine, and materials chemistry. The advances in the synthesis and knowledge of gold coordination compounds have been possible with the design of novel ligands becoming relevant motifs that have allowed the preparation of elusive complexes in this area of research. Strong donor ligands with easily modulable electronic and steric properties, such as stable singlet carbenes or cyclometalated ligands, have been decisive in the stabilization of gold(0) species, gold fluoride complexes, gold hydrides, unprecedented π complexes, or cluster derivatives. These new ligands have been important not only from the fundamental structure and bonding studies but also for the synthesis of sophisticated catalysts to improve activity and selectivity of organic transformations. Moreover, they have enabled the facile oxidative addition from gold(I) to gold(III) and the design of a plethora of complexes with specific properties.

Gold(I)-catalyzed intramolecular cyclization/intermolecular cycloaddition cascade as a fast track to polycarbocycles and mechanistic insights

Metal carbene is an active synthetic intermediate, which has shown versatile applications in synthetic chemistry. Although a variety of catalytic methods have been disclosed for the generation of carbene species from different precursors, there is an increasing demand for the development of efficient and practical approaches for the in-situ formation of metal carbene intermediates with structural diversity and unrevealed reactivity. Herein we report a gold-catalyzed cascade protocol for the assembly of polycarbocyclic frameworks in high yields under mild reaction conditions. Mechanistic studies indicate that the unique β-aryl gold-carbene species, generated via gold-promoted 6-endo-dig diazo-yne cyclization, is the key intermediate in this reaction, followed by a [4 + 2]-cycloaddition with external alkenes. In comparison to the well-documented metal carbene cycloadditions, this carbene intermediate serves as a 4-C synthon in a cycloaddition reaction. A variety of elusive π-conjugated polycyclic hydrocarbons (CPHs) with multiple substituents are readily accessible from the initially generated products by a mild oxidation procedure.

Recyclable heterogeneous gold(I)-catalyzed oxidative ring expansion of alkynyl quinols: a practical access to tropone and its analogues

The heterogeneous gold(i)-catalyzed oxidative ring expansion of alkynyl quinols has been achieved by using a benzyldiphenylphosphine-modified MCM-41-immobilized gold(i) complex [MCM-41-BnPh2P-AuNTf2] as the catalyst and 8-methylquinoline N-oxide as the oxidant under mild reaction conditions, yielding a variety of functionalized tropone derivatives in good to excellent yields. Extension of this methodology allows for facile construction of other seven- or six-membered ring systems including dibenzotropones, dibenzooxepines, phenanthrenes, and quinolin-2(1H)-ones. This new heterogeneous gold(i) complex can be readily recovered through a simple filtration process and recycled at least eight times without any apparent decrease in catalytic efficiency.

Gold(iii) promoted formation of dihydroquinazolinones: double X-H activation by gold

An efficient 2-furyl gold-carbene promoted synthetic method was developed for the formation of dihydroquinazolinones from enynones by dual insertion of anthranilamides. In this organic transformation a new C-O and two C-N bond formations occurred and dihydroquinazolinones were obtained with a quaternary centre in moderate to very good yields in one-pot synthesis.

The Molpro quantum chemistry package

Molpro is a general purpose quantum chemistry software package with a long development history. It was originally focused on accurate wavefunction calculations for small molecules but now has many additional distinctive capabilities that include, inter alia, local correlation approximations combined with explicit correlation, highly efficient implementations of single-reference correlation methods, robust and efficient multireference methods for large molecules, projection embedding, and anharmonic vibrational spectra. In addition to conventional input-file specification of calculations, Molpro calculations can now be specified and analyzed via a new graphical user interface and through a Python framework.

Fast Evaluation of Two-Center Integrals over Gaussian Charge Distributions and Gaussian Orbitals with General Interaction Kernels

We present efficient algorithms for computing two-center integrals and integral derivatives, with general interaction kernels K(r₁₂), over Gaussian charge distributions of general angular momenta l. While formulated in terms of traditional ab initio integration techniques, full derivations and required secondary information, as well as a reference implementation, are provided to make the content accessible to other fields. Concretely, the presented algorithms are based on an adaption of the McMurchie-Davidson Recurrence Relation (MDRR) combined with analytical properties of the solid harmonic transformation; this obviates all intermediate recurrences except the adapted MDRR itself, and allows it to be applied to fully contracted auxiliary kernel integrals. The technique is particularly well-suited for semiempirical molecular orbital methods, where it can serve as a more general and efficient replacement of Slater-Koster tables, and for first-principles quantum chemistry methods employing density fitting. But the formalism's high efficiency and ability of handling general interaction kernels K(r₁₂) and multipolar Gaussian charge distributions may also be of interest for modeling electrostatic interactions and short-range exchange and charge penetration effects in classical force fields and model potentials. With the presented technique, a 4894 × 4894 univ-JKFIT Coulomb matrix J_AB = (A|1/r₁₂|B) (183 MiB) can be computed in 50 ms on a Q2'2018 notebook CPU, without any screening or approximations.

Skeletal diversity in Pt- and Au-catalyzed annulations of allenedienes: dissecting unconventional mechanistic pathways

We describe the discovery of unprecedented annulation processes of 1,7-allenedienes, promoted by Pt or Au catalysts. These transformations revealed mechanistic pathways that had not been previously observed in reactions involving carbophilic catalysis. In particular, we have found that allenedienes bearing a silyl ether in the carbon tether connecting the diene and the allene divergently afford cyclopropane-embedded tricyclic derivatives, 6,6-fused bicarbocyclic products or 5,6-fused bicarbocyclic systems, depending on the type of Au or Pt catalyst used. We have carried out experimental and computational studies that shed light on the mechanistic reasons behind this rich and unusual skeletal divergence, and provide new lessons on the drastic influence of platinum ancillary ligands on the reaction outcome.

Oxidative Addition of Alkenyl and Alkynyl Iodides to a AuI Complex

The first isolated examples of intermolecular oxidative addition of alkenyl and alkynyl iodides to Au^I are reported. Using a 5,5'-difluoro-2,2'-bipyridyl ligated complex, oxidative addition of geometrically defined alkenyl iodides occurs readily, reversibly and stereospecifically to give alkenyl-Au^III complexes. Conversely, reversible alkynyl iodide oxidative addition generates bimetallic complexes containing both Au^III and Au^I centers. Stoichiometric studies show that both new initiation modes can form the basis for the development of C-C bond forming cross-couplings.

Anthranils: versatile building blocks in the construction of C–N bonds and N-heterocycles

This review article provides an overview of the recent progress in the transformations of anthranils, which have emerged as versatile building blocks in the assembly of various C–N bonds and medicinally active heterocyclic systems.

Allene-derived gold and platinum complexes: synthesis and first applications in catalysis

We report here the synthesis, full characterisation and first application in catalysis of novel Au(i), Au(iii) and Pt(ii) carbene-type complexes formed from bis(pyridyl)allenes. The catalytic activity of the new Au(i)-complexes in the cyclisation of 1,6-enynes, a benchmark reaction for new Au and Pt complexes, was comparable to Au(i)-state-of-the-art catalysts used in these reactions. Reactions with the new Au(iii)- and Pt(ii)-complexes occurred under milder conditions than those reported with AuCl3 and PtCl2.

σ-Noninnocence: Masked Phenyl-Cation Transfer at Formal NiIV

Reductive elimination is an elementary organometallic reaction step involving a formal oxidation state change of -2 at a transition-metal center. For a series of formal high-valent NiIV complexes, aryl-CF3 bond-forming reductive elimination was reported to occur readily (Bour et al. J. Am. Chem. Soc. 2015, 137, 8034-8037). We report a computational analysis of this reaction and find that, unexpectedly, the formal NiIV centers are better described as approaching a +II oxidation state, originating from highly covalent metal-ligand bonds, a phenomenon attributable to σ-noninnocence. A direct consequence is that the elimination of aryl-CF3 products occurs in an essentially redox-neutral fashion, as opposed to a reductive elimination. This is supported by an electron flow analysis which shows that an anionic CF3 group is transferred to an electrophilic aryl group. The uncovered role of σ-noninnocence in metal-ligand bonding, and of an essentially redox-neutral elimination as an elementary organometallic reaction step, may constitute concepts of broad relevance to organometallic chemistry.

Gold(i)-catalyzed stereoselective cyclization of 1,3-enyne aldehydes by a 1,3-acyloxy migration/Nazarov cyclization/aldol addition cascade

Stereoselective synthesis of bicyclo[3.3.0]octenones from chiral 1,3-enyne aldehydes bearing propargylic acetates is described. The method is based on a Au(i)-catalyzed domino sequence with concomitant transfer of chirality involving 1,3-acyloxy migration followed by Nazarov cyclization and an unprecedented aldol addition. The method furnishes densely functionalized bicyclic structures in high yields, with up to 97% ee and good diastereoselectivity.

Cationic Gold(I) Diarylallenylidene Complexes: Bonding Features and Ligand Effects

Using computational approaches, we qualitatively and quantitatively assess the bonding components of a series of experimentally characterized Au(I) diarylallenylidene complexes (N.Kim, R.A.Widenhoefer, Angew. Chem. Int. Ed. 2018, 57, 4722-4726). Our results clearly demonstrate that Au(I) engages only weakly in π-backbonding, which is, however, a tunable bonding component. Computationally identified trends in bonding are clearly correlated with the substitution patterns of the aryl substituents in the Au(I) diarylallenylidene complexes and good agreement is found with the previously reported experimental data, such as IR spectra, 13 C NMR chemical shifts and rates of decomposition together with their corresponding barrier heights, further substantiating the computational findings. The description of the bonding patterns in these complexes allow predictions of their spectroscopic features, their reactivity and stability.