Cyclization of gold acetylides: synthesis of vinyl sulfonates via gold vinylidene complexes

A β-Glucosyl Sterol Probe for in situ Fluorescent Labelling in Neuronal Cells to Investigate Neurodegenerative Diseases

A β-glucosyl sterol probe bearing a terminal alkyne moiety for fluorescent tagging enables the investigation of the neuronal and intracellular localization of this class of compounds involved in neurodegenerative diseases. The compound showed localization in the neuronal cells, with marked differences in the uptake and metabolism leading to enhanced persistence with respect to the un-glycosylated sterol analogue. In addition, a different impact was observed towards lysosomes, with the simple sterol probe showing the enlargement of the lysosome structures, while the β-glucosyl sterol was less capable to alter the morphology of this specific organelle.

Carbofunctionalization of Terminal Alkynes via Rhodium Catalysis Enabling Formations of Four Different Bonds

Described here is the oxygenative carbofunctionalization of terminal alkynes mediated by combined rhodium catalysis that enables regioselective quadruple formation of C-C, C-H, C-O, and C-heteroatom bonds. Mechanistic studies suggest that a disubstituted rhodium vinylidene complex is generated upon C-C bond formation at the terminal alkyne with tethered electrophiles such as alkyl halides, aldehydes, imines, and Michael acceptors. Subsequent intermolecular transfer oxygenation of the rhodium vinylidene with pyridine N-oxide generates a rhodium-complexed ketene intermediate that reacts with a variety of heteroatom nucleophiles to give rise to cyclic carboxylic acid derivatives.

Impact of counteranions on N-heterocyclic carbene gold(i)-catalyzed cyclization of propargylic amide

N-Heterocyclic carbene (NHC) Au(i)-catalyzed organic synthesis has recently been receiving increasing attention, especially with the activation of alkynes. In contrast, counteranions, being widely problematic in Au(i)-catalyzed transformations, are commonly considered as innocent partners and are not respectably included in a computational model. Herein, we report density functional theory (DFT) investigations of the Au(i)-catalyzed cyclization of propargylic amides to exploit the mechanistic effect of several counteranions to shed some light for further future developments. Among the counteranions used in this study, NTf₂ ^-, ClO₄ ^-, TsO^-, TFA^-, TfO^-, MsO^-, and SbF₆ ^-, both the cyclization and protodeauration step favor the 5-exo-dig product over the 6-endo-dig product when the alkyne moiety is terminated with hydrogen. These anions reveal a crucial influence on the energy profile through lowering the barriers of the reaction. Mechanistically, the results obtained from all counteranions show that the protodeauration is slower than the cyclization. By using an energetic span model, the results clearly indicate that the rate-determining state is the protodeauration step for all counteranions, and thus protodeauration is the turnover-limiting step. The turnover frequency (TOF) results for the formation of the 5-exo-dig product show cyclization reactivity in the order of MsO^- > TFA^- > ClO₄ ^- > NTf₂ ^- > TfO^- > TsO^- ≫ SbF₆ ^-, whereas an order of TFA^- > MsO^- > NTf₂ ^- > TfO^- ≈ ClO₄ ^- > SbF₆ ^- ⋙ TsO^- is calculated for the protodeauration, suggesting that SbF₆ ^- and TsO^- are disfavored due to their slow protodeauration. In this regard, and for the 6-endo-dig pathway, our conclusions demonstrate an order of TfO^- > TFA^- > MsO^- > NTf₂ ^- > ClO₄ ^- > TsO^- ⋙ SbF₆ ^- for the cyclization and TFA^- > TsO^- > MsO^- > TfO^- > NTf₂ ^- > ClO₄ ^- ⋙ SbF₆ ^- for the protodeauration, advocating that the anions SbF₆ ^-, NTf₂ ^- and ClO₄ ^- are unlikely partners for the 6-endo-dig pathway because of their slow protodeauration. Finally, the findings here advise that any engineering of the counteranion to increase the efficiency of catalytic system would be more effective on the protodeauration step rather than the cyclization step.

α-Rhenabenzofuran with nonaromatic T0 and aromatic S1 states

The first α-rhenabenzofuran complexes 2-5 are obtained from one-pot reactions of ReCl₃(PMePh₂)₃ with o-ethynyl phenols. With a delocalized structure, these paramagnetic compounds are nonaromatic at the ground state, which is a triplet. But they exhibit an aromatic singlet excited state, revealed by DFT studies.

Multicomponent Synthesis of Unsymmetrical 4,5-Disubstituted Imidazolium Salts as N-Heterocyclic Carbene Precursors: Applications in Palladium-Catalyzed Cross-Coupling Reactions

Various novel (a)chiral 4,5-disubstituted 1-aryl-3-alkyl-imidazolium salts were synthesized via the multicomponent reaction of diketone derivatives, sterically congested arylamines, and alkylamines. Moreover, two novel unsymmetrical bulky cycloalkyl-based NHC-Pd complexes proved highly active as catalysts for Suzuki-Miyaura and Negishi cross-coupling reactions.

Discovery and mechanism of action studies of 4,6-diphenylpyrimidine-2-carbohydrazides as utrophin modulators for the treatment of Duchenne muscular dystrophy

Duchenne muscular dystrophy is a fatal disease with no cure, caused by lack of the cytoskeletal protein dystrophin. Upregulation of utrophin, a dystrophin paralogue, offers a potential therapy independent of mutation type. The failure of first-in-class utrophin modulator ezutromid/SMT C1100 in Phase II clinical trials necessitates development of compounds with better efficacy, physicochemical and ADME properties and/or complementary mechanisms. We have discovered and performed a preliminary optimisation of a novel class of utrophin modulators using an improved phenotypic screen, where reporter expression is derived from the full genomic context of the utrophin promoter. We further demonstrate through target deconvolution studies, including expression analysis and chemical proteomics, that this compound series operates via a novel mechanism of action, distinct from that of ezutromid.

Dual gold catalysis - an update

This review summarizes the recent developments in the field of dual gold activation chemistry. New developments including synthetic strategies, latest mechanistic insights, computational studies and the identification and isolation of key intermediates, are discussed.

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis.

Dual Gold-Catalyzed Formal Tetradehydro-Diels-Alder Reactions for the Synthesis of Carbazoles and Indolines

This work reports a dual gold-catalyzed tetradehydro-Diels-Alder reaction for the synthesis of nitrogen-containing aromatic heterocycles. Under the catalytic system (IPrAuNTf₂ /DIPEA), indolines and carbazoles as well as other N-containing aromatic heterocycles were prepared in high yields with good functional group tolerance. Unlike the traditional thermal tetradehydro-Diels-Alder reactions, diluted reaction concentration and radical prohibitors are not required for this protocol. Experimental data support a mechanism involving gold vinylidene species, which undergoes a 6 π electrocyclization, followed with 1,2-hydrogen shift.

Gold-Catalyzed Formal Dehydro-Diels-Alder Reactions of Ene-Ynamide Derivatives Bearing Terminal Alkyne Chains: Scope and Mechanistic Studies

A new protocol for the synthesis of a variety of N-containing aromatic heterocycles by a formal gold-catalyzed dehydro-Diels-Alder reaction of ynamide derivatives has been developed. Deuterium-labeling experiments and kinetic studies support the involvement of a dual gold catalysis mechanism in which a gold acetylide moiety adds onto an aurated keteneiminium.

N-Heterocyclic carbene copper-catalyzed direct alkylation of terminal alkynes with non-activated alkyl triflates

(NHC)-Cu-catalyzed C(sp)-C(sp³) bond formation has been successfully achieved under mild conditions. Nonactivated alkyl triflates, which could be easily derived from alcohols, were utilized as C-O electrophiles. Mechanistic studies suggested that copper acetylide was the active species. Scale-up reactions further demonstrated the practicality and efficiency of the developed strategy.

A Golden Access to Acenopentalenes

By employing gold catalysis, starting from dialkynylated acenes a series of novel un-symmetrical aceno-annulated dibenzopentalenes has been prepared. The achieved yields range from 62-68 %. The fused systems contain naphthalene, anthracene, tetracene, and pentacene units. All new compounds are soluble and stable under standard conditions. The optical properties of the systems are dominated by the dibenzopentalene core for the smaller representatives, while for the anthracene-pentacene-based aceno-benzopentalenes the optical properties of the acene group dominates. Preliminary morphology tests on thin films showed a reverse trend between crystal size and molecule size.

Gold-alkynyls in catalysis: alkyne activation, gold cumulenes and nuclearity

The use of cationic gold(i) species in the activation of substrates containing C[triple bond, length as m-dash]C bonds has become a valuable tool for synthetic chemists. Despite the seemingly simple label of 'alkyne activation', numerous patterns of reactivity and product structure are observed in systems employing related substrates and catalysts. The complications of mechanistic determination are compounded as the number of implicated gold(i) centres involved in catalysis increases and debate about the bonding in proposed intermediates clouds the number and importance of potential reaction pathways. This perspective aims to illustrate some of the principles underpinning gold-alkynyl interactions whilst highlighting some of the contentious areas in the field and offering some insight into other, often ignored, mechanistic possibilities based on recent findings.

Synthesis of azulene-substituted benzofurans and isocoumarins via intramolecular cyclization of 1-ethynylazulenes, and their structural and optical properties

The preparation of azulene-substituted benzofurans and isocoumarins was established by two types of intramolecular cyclization reaction of 1-ethynylazulenes.

Cyclization Reactions of Aryl Propargyl Acetates with Tethered Epoxide Induced by Ruthenium Complex

Reactions of the ruthenium complex [Ru]Cl ([Ru]=Cp(PPh₃ )₂ Ru; Cp=η⁵ -C₅ H₅ ) with several aryl propargyl acetates, each with an ortho-substituted chain of various length containing an epoxide on the aromatic ring and with or without methyl substitutents on the epoxide ring, bring about novel cyclizations. The cyclization reactions of HC≡CCH(OAc)(C₆ H₄ )CH₂ (RC₂ H₂ O) (R=H, 6 a; R=CH₃ , 6 b, where RC₂ H₂ O is an epoxide ring) in MeOH give the vinylidene complexes 5 a-b, respectively, each with the Cβ integrated into a tetrahydro-5H-benzo[7]annulen-6-ol ring. A C-C bond formation takes place between the propargyl acetate and the less substituted carbon of the epoxide ring. Further cyclizations of 5 a-b induced by HBF₄ give the corresponding vinylidene complexes 8 a-b each with a new 8-oxabicyclo-[3.2.1]octane ring by removal of a methanol molecule in high yield. For similar aryl propargyl acetates with a shorter epoxide chain, the cyclization gives a mixture of a vinylidene complex with a tetrahydronaphthalen-1-ol ring and a carbene complex with a tricyclic indeno-furan ring. For the cyclization of 18, with a longer epoxide chain, opening of the epoxide is required to afford the vicinal bromohydrin 22, then tandem cyclization occurs in one pot. Products are characterized by spectroscopic methods as well as by XRD analysis.

On the Gold-Catalyzed Generation of Vinyl Cations from 1,5-Diynes

Conjugated 1,5-diynes bearing two aromatic units at the alkyne termini were converted in the presence of a gold catalyst. Under mild conditions, aryl-substituted dibenzopentalenes were generated. Calculations predict that aurated vinyl cations are key intermediates of the reaction. A bidirectional approach provided selective access to the angular annulated product in high yield, which was explained by calculations.

Self-assembled core–shell-corona multifunctional non-viral vector with AIE property for efficient hepatocyte-targeting gene delivery

Core–shell-corona multifunctional nanoparticles were prepared and used for cell imaging and cell-targeting delivery of genes toward hepatocytes.

Five-State Rotary Nanoswitch

In our quest to develop artificial multistate devices, we synthesized the nanomechanical switch 1 that is characterized by a tetrahedral core equipped with four pending arms. The rotary arm with its azaterpyridine terminal is intramolecularly coordinated to a zinc(II) porphyrin station that is the terminus of another arm in 1. The two other arms carry identical sterically shielded phenanthroline stations. The 2-fold alternate addition of a copper(I) ion and [1,10]-phenanthroline (1 equiv each) results in the formation of five different switching states (State I→ State II→ State III→ State IV→ State V → State I), which force the toggling arm to move back and forth between the zinc(II) porphyrin and phenanthroline stations separated by a distance of 25 Å. All switching states constitute clean single species, except for State III, and thus are fully characterized by spectroscopic methods and elemental analysis. Finally, the initial state of nanoswitch was reset by addition of cyclam for complete removal of the copper(I) ions.