Coupling Reactions of Alkynylsilanes Mediated by a Cu(I) Salt: Novel Syntheses of Conjugate Diynes and Disubstituted Ethynes

Palladium-Catalyzed Cross-Coupling of Aryl Bromides and Chlorides with Trimethylsilylalkynes under Mild Conditions

Herein, we disclose a palladium-catalyzed cross-coupling of aryl bromides and chlorides with trimethylsilylalkynes under mild reaction conditions. This method utilizes commercially available and air stable palladium precatalysts and avoids the use of copper cocatalysts. Moreover, it allows for the synthesis of a wide range of disubstituted alkynes in high yields with excellent functional group tolerance. The utility of the developed method was further demonstrated via the late-stage alkynylation of pharmaceuticals and natural bioactive compounds.

A Simple and Practical Bis-N-Heterocyclic Carbene as an Efficient Ligand in Cu-Catalyzed Glaser Reaction

Conjugated diyne derivatives are important scaffolds in modern organic synthetic chemistry. Using the Glaser reaction involves the coupling of terminal alkynes which can efficiently produce conjugated diyne derivatives, while the use of a stoichiometric amount of copper salts, strong inorganic base, and excess oxidants is generally needed. Developing an environmentally friendly and effective method for the construction of symmetrical 1,3-diynes compounds by Glaser coupling is still highly desirable. In this study, we present an economical method for the production of symmetric diynes starting from various terminal acetylenes in a Glaser reaction. A simple and practical bis-N-heterocyclic carbene ligand has been introduced as efficient ligands for the Cu-catalyzed Glaser reaction. High product yields were obtained at 100 °C for a variety of substrates including aliphatic and aromatic terminal alkynes and differently substituted terminal alkynes including the highly sterically hindered substrate 2-methoxy ethynylbenzene or 2-trifluoromethyl ethynylbenzene and a series of functional groups, such as trifluoromethyl group, ester group, carboxyl group, and nitrile group. The established protocol is carried out in air under base-free condition and is operationally simple. These research work suggest that bis-N-heterocyclic carbene could also an appealing ligand for Glaser reaction and provide a reference for the preparation of symmetric 1,3-diynes in industrial filed.

Fused diethynylbenzenes and phenanthrenes via arynes with alkynylsilanes

A method for the hydroalkynylation and catalytic cyclization reactions of hexadehydro-Diels-Alder-derived benzynes is described. Diethynylbenzene derivatives are generated in a one-step reaction via trimethylsilyl-alkyne groups with benzyne formed by heating the appropriate tetrayne substrate. Trimethyl(phenylethynyl)silane loses TMS and binds to the electron-deficient site on HDDA-derived benzynes, and then phenanthrene was synthesized under mild reaction conditions by transition-metal-free, base promoted intramolecular cyclization.

A Deprotection-free Method for High-yield Synthesis of Graphdiyne Powder with In Situ Formed CuO Nanoparticles

With a direct band gap, superior charge carrier mobility, and uniformly distributed pores, graphdiyne (GDY) has stimulated tremendous interest from the scientific community. However, its broad application is greatly limited by the complicated multistep synthesis process including complex deprotection of hexakis-[(trimethylsilyl)ethynyl]benzene (HEB-TMS) and peeling of GDY from the substrates. Here, we describe a deprotection-free strategy to prepare GDY powder by directly using HEB-TMS as the monomer. When CuCl was used as the catalysts in DMF solvent, the yield of GDY powder reached ≈100 %. More interestingly, uniformly dispersed CuO nanoparticles with an average diameter of ≈2.9 nm were in situ formed on GDY after the reaction. The prepared CuO/GDY was demonstrated an excellent co-catalyst for photocatalytic hydrogen evolution, comparable to the state-of-art Pt co-catalyst. The deprotection-free approach will widen the use of GDY and facilitate its scaling up to industrial level.

Iron-Catalyzed Cadiot-Chodkiewicz Coupling with High Selectivity in Water under Air

An iron-based catalytic system was developed for the cross-coupling of 1-bromoalkynes with terminal alkynes to selectively generate unsymmetrical 1,3-butadiynes in water under air. It was found that a combination of 1-bromoalkynes derived from less acidic terminal alkynes with more acidic counterparts would greatly enhance yields and selectivity for unsymmetrical 1,3-butadiynes. The reaction was also applicable for the synthesis of unsymmetrical 1,3,5-hexatriynes through coupling of 1-bromoalkynes and trimethylsilyl-protected 1,3-butadiynes in a one-pot manner.

Pd-PEPPSI N-Heterocyclic Carbene Complexes from Caffeine: Application in Suzuki, Heck, and Sonogashira Reactions

The first synthesis of Pd-PEPPSI N-heterocyclic carbene complexes derived from the abundant and renewable natural product caffeine is reported. The catalysts bearing 3-chloro-pyridine, pyridine and N-methylimidazole ancillary ligands were readily prepared from the corresponding N9-Me caffeine imidazolium salt by direct deprotonation and coordination to PdX2 in the presence of N-heterocycles or by ligand displacement of PdX2(Het)2. The model Pd-PEPPSI-caffeine complex has been characterized by x-ray crystallography. The complexes were successfully employed in the Suzuki cross-coupling of aryl bromides, Suzuki cross-coupling of amides, Heck cross-coupling and Sonogashira cross-coupling. Computational studies were employed to determine frontier molecular orbitals and bond order analysis of caffeine derived Pd-PEPPSI complexes. This class of catalysts offers an entry to utilize benign and sustainable biomass-derived Xanthine NHC ligands in the popular Pd-PEPPSI systems in organic synthesis and catalysis.

Recent Advances in Transition-metal-catalyzed C-C Bond Formation via C(sp2 )-F Bond Cleavage

The activation of a carbon-fluorine bond is one of the most challenging topics in modern synthetic organic chemistry due to their low reactivity compared to other carbon-halogen bonds. In this review, we present the recent developments since 2015 on cross-coupling reactions that form C-C bonds via cleavage of C(sp² )-F bonds. Not only the conventional activation of C(sp² )-F bonds, but also decarbonylative or carbonyl-retentive cleavage of C(acyl)-F bonds will be introduced. This paper mainly describes new protocols for the formation of C(sp² )-C(sp³ ), C(sp² )-C(sp² ), and C(sp² )-C(sp) bonds via transition-metal-catalyzed cleavage of C(sp² )-F bonds.

A General and Highly Selective Palladium-Catalyzed Hydroamidation of 1,3-Diynes

A chemo-, regio-, and stereoselective mono-hydroamidation of (un)symmetrical 1,3-diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α-alkynyl-α, β-unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density-functional theory (M06L-SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3-diynes.

Tailored Palladium Catalysts for Selective Synthesis of Conjugated Enynes by Monocarbonylation of 1,3-Diynes

For the first time, the monoalkoxycarbonylation of easily available 1,3-diynes to give synthetically useful conjugated enynes has been realized. Key to success was the design and utilization of the new ligand 2,2'-bis(tert-butyl(pyridin-2-yl)phosphanyl)-1,1'-binaphthalene (Neolephos), which permits the palladium-catalyzed selective carbonylation under mild conditions, providing a general preparation of functionalized 1,3-enynes in good-to-high yields with excellent chemoselectivities. Synthetic applications that showcase the possibilities of this novel methodology include an efficient one-pot synthesis of 4-aryl-4H-pyrans as well as the rapid construction of various heterocyclic, bicyclic, and polycyclic compounds.

Palladium/copper-cocatalyzed decarbonylative alkynylation of acyl fluorides with alkynylsilanes: synthesis of unsymmetrical diarylethynes

Alkynylation of acyl fluorides with alkynylsilanes via palladium/copper-cocatalysed carbon–fluorine bond cleavage and sequential decarbonylation, which provide an efficient route to various unsymmetrical diarylethynes, have been disclosed.

Graphdiyne: synthesis, properties, and applications

Graphdiyne (GDY), a new two-dimensional (2D) carbon allotrope, has been receiving increased attention. Its unique sp-sp2 carbon atoms, uniform pores, and highly π-conjugated structure provide promising potential in practical applications, such as gas separation, catalysis, water remediation, humidity sensor, and energy-related fields. In the recent years, considerable efforts have been expended toward the development of well-defined GDY. However, GDY materials still face numerous challenges, including the need for a more thorough understanding of the growth mechanism, strategies for synthesizing one- or few-layer single-crystalline GDY films, characterization of basic physicochemical properties, and achievement of promising applications. This review aims at providing a comprehensive update on the synthesis of GDY and GDY-based materials, as well as their properties, including structural, electronic, mechanical, and spectral properties, and their applications in nanotechnology.

Benzotriazole as an Efficient Ligand in Cu-Catalyzed Glaser Reaction

Benzotriazole has been established as an efficient ligand in Cu-catalyzed cross-coupling of terminal alkynes to form 1,3-dialkynes using CuI as the catalyst and K2CO3 as the base at room temperature in an open round-bottom flask. The established protocol has the following notable advantages: simple to handle, easy work-up, mild reaction condition, high substrate scope, requirement of less quantity of ligand and also Cu-catalyst, less expensive, and high reaction yield.

Probing enantioselectivity in rhodium-catalyzed Si–C bond cleavage to construct silicon-stereocenters: a theoretical study

Density functional theory (DFT) calculations indicate that favorable oxidative addition/reductive elimination process from arylrhodium complex determines the enantioselectivity.

Designing Cross-Coupling Reactions using Aryl(trialkyl)silanes

Organo(trialkyl)silanes have several advantages, including high stability, low toxicity, good solubility, easy handling, and ready availability compared with heteroatom-substituted silanes. However, methods for the cross-coupling of organo(trialkyl)silanes are limited, most probably because of their exceeding robustness. Thus, a practical method for the cross-coupling of organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses how aryl(trialkyl)silanes can be used in cross-coupling reactions. A pioneering example is Cu^II catalytic conditions with the use of electron-accepting aryl- or heteroaryl(triethyl)silanes and aryl iodides. The reaction forms biaryls or teraryls. This design concept can be extended to Pd/Cu^II -catalyzed cross-coupling polymerization reactions between such silanes and aryl bromides or chlorides and to Cu^I -catalyzed alkylation using alkyl halides.

Copper(i)/succinic acid cooperatively catalyzed one-pot synthesis of organoselenium-propargylamines via A3-coupling

Selenium propargylamines were synthesized via an A³-coupling approach using piperidine, p-methoxybenzaldehyde, and trimethylsilyl selenium–acetylene, catalyzed by copper(i) chloride and succinic acid as an additive, in good to excellent yields.

Visible light mediated desilylative C(sp2)–C(sp2) cross-coupling reactions of arylsilanes with aryldiazonium salts under Au(i)/Au(iii) catalysis

Desilylative C(sp²)–C(sp²) cross-coupling reactions of arylsilanes with aryldiazonium salts under Au(i)/photoredox catalysis have been reported.

Deprotonative Silylation of Aromatic C-H Bonds Mediated by a Combination of Trifluoromethyltrialkylsilane and Fluoride

A method for the deprotonative silylation of aromatic C-H bonds has been developed using trifluoromethyltrimethylsilane (CF₃SiMe₃, Ruppert-Prakash reagent) and a catalytic amount of fluoride. In this reaction, CF₃SiMe₃ is considered to act as a base and a silicon electrophile. This process is highly tolerant to various functional groups on heteroarenes and benzenes. Furthermore, this method can be applied to the synthesis of trimethylsilyl group-containing analogs of TAC-101, which is a bioactive synthetic retinoid with selective affinity for retinoic acid receptor α (RAR-α) binding. We also report further transformations of the silylated products into useful derivatives.

Highly efficient synthesis of unsymmetrical 1,3-diynes from organoalane reagents and alkynyl bromides mediated by a nickel catalyst

Highly efficient and simple cross-coupling reactions of alkynylbromides with organoalane reagents for the synthesis of unsymmetrical 1,3-diynes derivatives using Ni(OAc)₂ (2–5 mol%)/(o-furyl)₃P (4–10 mol%) as a catalyst are reported.

Synthesis of Multisubstituted Olefins through Regio- and Stereoselective Addition of Interelement Compounds Having B-Si, B-B, and Cl-S Bonds to Alkynes, and Subsequent Cross-Couplings

Multisubstituted olefins are fundamental motifs in organic compounds. In this account, we describe the synthesis of organic molecules bearing an olefinic moiety by the transition-metal-catalyzed regio- and stereoselective addition of a variety of interelement compounds to alkynes. Regio- and stereoselective silaboration, diborylation, and chlorothiolation have been achieved by using the transition-metal catalysts. The subsequent cross-coupling reactions of the boron-containing alkenes to install various aryl groups afforded the corresponding tri- and tetraarylated olefins. This account describes our research on the highly regio- and stereoselective synthesis of multifunctionalized olefins such as tetraarylethenes with four different aryl groups.

Experimental and theoretical studies of spectroscopic properties of simple symmetrically substituted diphenylbuta-1,3-diyne derivatives

A series of symmetrically substituted diphenylbuta-1,3-diyne (DPB) derivatives possessing electron-donating (N,N-dimethylamino or methoxy) or electron-accepting (nitrile, ester or aldehyde) groups have been prepared and studied with emphasis on their spectral and photophysical properties. The photophysical characteristics of these compounds have been studied in relation to their structures and influence of solvents or temperature. The observed spectral and photophysical properties are explained with the help of potential energy maps in the ground and excited states obtained from density functional theory (DFT, B3LYP, def2TZVP basis set) calculations. The structure-property relationship of all of the compounds is discussed and compared with appropriate diphenylacetylene derivatives.