Bifunctional Ligand Enables Gold-Catalyzed Propargyl C-H Functionalization via Reactive Gold Allenylidene Intermediate.

Gold allenylidene species have been seldom exploited as reactive intermediates in synthetically versatile catalytic reactions. By employing alkynylbenziodoxoles as the substrates and bifunctional WangPhos as the metal ligand, this work demonstrated ready catalytic access to these intermediates of general substitution patterns and their electrophilic reactivities at the γ-carbon center with a diverse range of nucleophiles. The reaction is driven by the reductive decomposition of the benziodoxole moiety and achieves the replacement of a propargylic proton with an N/O/C-based nucleophile, hence realizing reactivity umpolung. Corroborated by Density Functional Theory (DFT) calculations, the reaction mechanism involves a mild propargylic deprotonation. In contrast to prior works employing a tertiary amine functionality, a weakly BrØnsted-basic amide group in WangPhos is surprisingly effective in deprotonation at the propargylic position under a gold-ligand cooperation regime.

Reactivities of α-Oxo BMIDA Gold Carbenes Generated by Gold-Catalyzed Oxidation of BMIDA-Terminated Alkynes.

An oxidative strategy is reported to access α-oxo BMIDA gold carbenes directly from BMIDA-terminated alkynes. Besides offering expedient access to seldom studied boryl metal carbenes, these BMIDA gold carbene species undergo facile insertions into methyl, methylene, methine, and benzylic C-H bonds in the absence of the Thorpe-Ingold effect. They also undergo efficient OH insertion, cyclopropanation, and F-C alkylations. This chemistry provides rapid access to structurally diverse α-BMIDA ketones, which are scarcely documented. In combination with DFT studies, the role of BMIDA is established to be an electron-donating group that attenuates the high electrophilicity of the gold carbene center.

[Sleep-improving mechanism of Chaiqin Ningshen Granules in insomnia rats: based on hippocampal metabonomics].

With the ultra high performance liquid chromatography-quadruple-electrostatic field orbitrap high resolution mass spectrometry(UHPLC-Q Exactive Orbitrap-MS)-based metabonomics technology, this study aims to analyze the effect of Chaiqin Ningshen Granules(CNG) on endogenous metabolites in insomnia rats of liver depression syndrome and explore the sleep-improving mechanism of this prescription. Parachlorophenylalanine(PCPA, ip) and chronic stimulation were combined to induce insomnia of liver depression pattern in rats, and the effect of CNG on the macroscopic signs, hemorheology, and neurotransmitters in the hippocampus of insomnia rats of liver depression syndrome was observed. After the administration, rat hippocampus was collected for liquid chromatography-mass spectrometry(LC-MS) analysis of the metabolomics. Principal component analysis(PCA), partial least squares discriminant analysis(PLS-DA), and orthogonal partial least squares discriminant analysis(OPLS-DA) were employed for analyzing the metabolites in rat hippocampus and screening potential biomarkers. MetPA was used to yield the related metabolic pathways and metabolic networks. The results show that the drugs can significantly improve the mental state, liver depression, and blood stasis of rats, significantly increase the content of 5-hydroxytryptamine(5-HT) and gamma aminobutyric acid(GABA) in hippocampus(except low-dose CNG), and significantly reduce the content of glucose(Glu)(except low-dose CNG). Among them, estazolam and high-dose CNG had better effect than others. Metabolomics analysis yielded 27 potential biomarkers related to insomnia. MetPA analysis showed 4 metabolic pathways of estazolam in intervening insomnia and 3 metabolic pathways of high-dose CNG in intervening insomnia, involving purine metabolism, glycerophospholipid metabolism, histidine metabolism, and caffeine metabolism. CNG can alleviate insomnia by regulating endogenous differential metabolites and further related metabolic pathways. The result lays a basis for further elucidating the mechanism of CNG in improving sleep.

Mechanism of Hypervalent Iodine Promoted Fluorocyclization of Unsaturated Alcohols: Metathesis via Double Acids Activation.

Lewis/Bronsted acid activation plays a key role in hypervalent iodine reagent-mediated reactions. In addition to generally accepted cis-activation or trans-activation, this study reveals another important Lewis/Bronsted acid activation mode, the double-activation. Different from the generally proposed iodine(III)iranium SN2 mechanism, the hypervalent difluoro-iodoarene-promoted fluorocyclization of unsaturated alcohol prefers to undergo the metathesis mechanism via an iodine(III)-π intermediate.

Hierarchical Gelation of a Pd12L24 Metal-Organic Cage Regulated by Cholesteryl Groups.

The creation of supramolecular assemblies by assembly of structurally simple components via supramolecular interactions provides an opportunity to develop functional materials with hierarchical complexibility. Herein, we report an assembly approach to supramolecular gels based on metal-organic cages with tunable hierarchical structures and properties. A Pd12L24 cage (L is cholesteryl-functionalized 3,5-bis(4-pyridyl)benzene) bearing 24 cholesteryl groups is used as a supramolecular building unit and molecular platform for functionalization with tunable functional behaviors. The Pd12L24 cage motifs spontaneously self-assemble into gels where orthogonal metal-organic coordination and cholesteryl-cholesteryl interactions are involved in the gelation. The Pd12L24 cage exhibits a reversible transition between solution and aggregated gel states in response to temperature. The gelation and the mechanical property are rarely regulated by deuterated solvents and tetramethylsilane. The mechanical property of the gel materials is tunable by varying the content of cholesteryl groups of Pd12L24. Functional moieties (e.g., luminescent TPE group) can be introduced on the cage, and the luminescent property changes while the structure is maintained. The Pd12L24 gel shows visible anion-responsive behaviors arising from the hierarchical structure.

Merging Distal Alkynyl Migration and Photoredox Catalysis for Radical Trifluoromethylative Alkynylation of Unactivated Olefins.

Disclosed herein is a novel, redox-neutral protocol for the visible-light-induced radical alkynylation of unactivated olefins. The intramolecular migration of an alkynyl group, by cleaving an inert C-C σ bond, is realized for the first time. A wide range of synthetically useful trifluoroethylated linear alkynes are readily obtained under mild reaction conditions.

Copper-Catalyzed Regioselective C-H Sulfonylation of 8-Aminoquinolines.

Copper(I)-catalyzed 5-sulfonation of quinolines via bidentate-chelation assistance has been developed. The reaction is compatible with a wide range of quinoline substrates and arylsulfonyl chlorides. Experimental and theoretical (DFT) investigation implicated that a single-electron-transfer process is involved in this sulfonylation transformation.

Rationalization of the selectivity between 1,3- and 1,2-migration: a DFT study on gold(i)-catalyzed propargylic ester rearrangement.

Gold catalyzed rearrangement of propargylic esters can undergo 1,3-acyloxy migration to form allenes, or undergo 1,2-acyloxy migration to access gold-carbenoids. The variation in migration leads to different reactivities and diverse cascade transformations. The effect of terminal substituents is very important for the rearrangement. However, it remains ambiguous how terminal substituents govern the selectivity of the rearrangement. This study presents a theoretical model based on the resonance structure of gold activated propargylic ester complexes to rationalize the rearrangement selectivity. Substrates with a major resonance contributor A prefer 5-exo-dig cyclization (1,2-migration), while those with a major resonance contributor B prefer 6-endo-dig cyclization (1,3-migration). This concise model would be helpful in understanding and tuning the selectivity of the metal catalyzed rearrangement of propargylic esters.

The effect of HSAB on stereoselectivity: copper- and gold-catalyzed 1,3-phosphatyloxy and 1,3-halogen migration relay to 1,3-dienes.

The origin of stereodivergence between copper- and gold-catalyzed cascade 1,3-phosphatyloxy and 1,3-halogen migration from α-halo-propargylic phosphates to 1,3-dienes is rationalized with density functional theory (DFT) studies. Our studies reveal the significant role of the relative hardness/softness of the metal centers in determining the reaction mechanism and the stereoselectivity. The relative harder Cu(I/III) center prefers an associative pathway with the aid of a phosphate group, leading to the (Z)-1,3-dienes. In contrast, the relative softer Au(I/III) center tends to undergo a dissociative pathway without coordination to a phosphate group, resulting in the (E)-1,3-dienes, where the E type of transition state is favored due to the steric effect. Our findings indicate the intriguing role of hard-soft/acid-base (HSAB) theory in tuning the stereoselectivity of metal-catalyzed transformations with functionalized substrates.

Solution structure of a thrombin binding aptamer complex with a non-planar platinum(ii) compound.

Thrombin Binding Aptamer (TBA) is a monomolecular well-defined two G-tetrad antiparallel G-quadruplex DNA that inhibits the activity of human α-thrombin. In this report, we synthesized a quasi-cross-shaped platinum(ii) compound (L'2LPt) with one cyclometalated and two carbene ligands. We found L'2LPt has selective affinity to bind the TBA G-quadruplex. A fibrinogen clotting assay revealed that L'2LPt can abrogate the inhibitory activity of TBA against thrombin. We solved the 1 : 1 L'2LPt-TBA complex structure by NMR, which revealed a unique self-adaptive property of L'2LPt upon binding to TBA. In the complex, a carbene ligand of L'2LPt rotates to pair with the cyclometalated ligand to form a plane stacking over half of the TBA G-tetrad and covered by lateral TT loops. It is notable that the heavy atom Pt stays out of the G-tetrad. Meanwhile, the other carbene ligand remains relatively perpendicular and forms a hydrogen bond with a guanine to anchor the L'2LPt position. This structure exhibits a quasi-cross-shaped Pt(ii) compound bound to the G-quadruplex with an unusual "wall-mounted" binding mode. Our structures provide insights into the specific recognition of antiparallel G-quadruplex DNA by a self-adaptive Pt(ii) compound and useful information for the design of selective G-quadruplex targeting non-planar molecules.

Incorporation of H2O and CO2 into a BN-embedded 3aH-3a1H-acephenanthrylene derivative.

A fused tetracyclic BN-species 1 featuring nucleophilic nitrogen and electrophilic boron centers behaves as a reactive N/B frustrated Lewis pair (FLP) for small molecule activation. Specifically, the O-H and C[double bond, length as m-dash]O bonds have been cleaved by 1 with the formation of fused borinic acid 2, borenium species 3, anionic boranuidacarboxylic acid 4 and oxadiazaborolidinone 5, respectively. Quantum-mechanical calculations are conducted to comprehensively understand the activation processes of small molecules by 1.

BNN-1,3-dipoles: isolation and intramolecular cycloaddition with unactivated arenes.

The mono-base-stabilized 1,2-diboranylidenehydrazine derivatives featuring a 1,3-dipolar BNN skeleton are obtained by dehydrobromination of [ArB(Br)NH]2 (Ar = 2,6-diphenylphenyl (Dpp), Ar = 2,6-bis(2,4,6-trimethylphenyl)phenyl (Dmp) or Ar = 2,4,6-tri-tert-butylphenyl (Mes*)) with N-heterocyclic carbenes (NHCs). Depending on the Ar substituents, such species can be isolated as a crystalline solid (Ar = Mes*) or generated as reactive intermediates undergoing spontaneous intramolecular aminoboration of the proximal arene rings via [3 + 2] cycloaddition (Ar = Dpp or Dmp). The latter reactions showcase the 1,3-dipolar reactivity toward unactivated arenes at ambient temperature. In addition, double cycloaddition of the isolable BNN species with two CO2 molecules affords a bicyclic species consisting of two fused five-membered BN2CO rings. The electronic structures of these BNN species and the mechanisms of these cascade reactions are interrogated through density functional theory (DFT) calculations.

Unraveling mechanisms of the uncoordinated nucleophiles: theoretical elucidations of the cleavage of bis(p-nitrophenyl) phosphate mediated by zinc-complexes with apical nucleophiles.

A theoretical approach was used to investigate the hydrolytic cleavage mechanisms of the bis(p-nitrophenyl) phosphate (BNPP-) catalyzed by Zn(ii)-complexes featuring uncoordinated nucleophiles. Ligand-based and alternative solvent-based nucleophilic attack reaction models are proposed. The pK a values of the Zn(ii)-bound water molecules or ligands in the [Zn(L n H)(η-H2O)(H2O)]2+ (n = 1, 2 and 3) complexes, as well as the dimerization tendency of the mononuclear Zn(ii)-complexes, were found to significantly influence the reaction mechanisms. The Zn(ii)-L3 complexes were found to be more favorable for the hydrolytic cleavage of the BNPP- via a ligand-based nucleophilic attack pathway. This was due to the lower pK a value for the deprotonation of the oxime ligand, the hard dimerization of the mononuclear Zn(ii)-L3 species, and the presence of an uncoordinated nucleophile. The origins of the uncoordinated reactions were systematically elucidated. The theoretical results reported here are in good agreement with experimental observations and more importantly, help to elucidate the factors that influence intermolecular nucleophilic attack reactions with coordinated/uncoordinated nucleophiles.

Ruthenium-Catalyzed Direct Synthesis of Semisaturated Bicyclic Pyrimidines via Selective Transfer Hydrogenation.

A new ruthenium-catalyzed direct and selective synthesis of semisaturated bicyclic pyrimidines, from α-aminopyridyl alcohols and nitriles, has been demonstrated. The synthesis proceeds with an easily available catalyst system, broad substrate scope, excellent functional tolerance, and no need for high pressure H2 gas. Control experiments indicate that the reaction proceeds via successive dehydrogenative annulation and transfer hydrogenation of the less electrophilic pyridyl nucleus, and the density functional theory (DFT) study reveals the origin of such a unique selectivity.

Unusual non-bifunctional mechanism for Co-PNP complex catalyzed transfer hydrogenation governed by the electronic configuration of metal center.

The mimic of hydrogenases has unleashed a myriad of bifunctional catalysts, which are widely used in the catalytic hydrogenation of polar multiple bonds. With respect to ancillary ligands, the bifunctional mechanism is generally considered to proceed via the metal-ligand cooperation transition state. Inspired by the interesting study conducted by Hanson et al. (Chem Commun., 2013, 49, 10151), we present a computational study of a distinctive example, where a Co(II)-PNP catalyst with an ancillary ligand exhibits efficient transfer hydrogenation through a non-bifunctional mechanism. Both the bifunctional and non-bifunctional mechanisms are discussed. The calculated results, which are based on a full model of the catalyst, suggest that the inner-sphere non-bifunctional mechanism is more favorable (by ∼11 kcal mol(-1)) than the outer-sphere bifunctional mechanism, which is in agreement with the experimental observations. The origin of this mechanistic preference of the Co(II)-PNP catalyst can be attributed to its preference for the square planar geometry. A traditional bifunctional mechanism is less plausible for Co(II)-PNP due to the high distortion energy caused by the change in electronic configuration with the varied ligand field. Considering previous studies that focus on the development of ligands more often, this computational study indicates that the catalytic hydrogenation mechanism is controlled not only by the structure of the ligand but also by the electronic configuration of the metal center.