Development of Sulfonic-Acid-Functionalized Mesoporous Materials: Synthesis and Catalytic Applications

Sulfonic acid based mesostructures (SAMs) have been developed in recent years and have important catalytic applications. The primary applications of these materials are in various organic synthesis reactions, such as multicomponent reactions, carbon–carbon bond couplings, protection reactions, and Fries and Beckman rearrangements. This review aims to provide an overview of the recent developments in the field of SAMs with a particular emphasis on the reaction scope and advantages of heterogeneous solid acid catalysts.     

Visible-light-mediated cascade difunctionalization/cyclization of alkynoates with acyl chlorides for synthesis of 3-acylcoumarins

A new visible-light-mediated radical cyclization of alkynoates with acyl chlorides is described for the one-pot construction of diverse 3-acylcoumarins with high efficiency and selectivity. This method is successful by sequential difunctionalization of an alkynes CC triple bond with the CCl bonds of acyl chloride and aromatic C(sp²)H bonds. The cyclization is proposed to simultaneously form two new carbon–carbon bonds, and involves radical acylation, 5-exo-trig cyclization, and ester migration.     

DFT-assisted design and evaluation of bifunctional copper(I) catalysts for the direct intermolecular addition of aldehydes and ketones to alkynes

Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation.     

Chiral vanadyl salen complex anchored on supports as recoverable catalysts for the enantioselective cyanosilylation of aldehydes. Comparison among silica, single wall carbon nanotube, activated carbon and imidazolium ion as support

The activity and enantiomeric excess (ee) (in some cases >85%) obtained for the asymmetric addition of trimethylsilyl cyanide to aldehydes using different heterogeneous chiral catalysts are compared. A library of recoverable catalysts was developed by immobilization of a chiral vanadyl salen complex having a terminal carbon-carbon double bond onto a series of scaffolds including silica, single-wall carbon nanotubes, activated carbon and room-temperature ionic liquids. The covalent linkage has been achieved by radical initiated addition of mercapto groups to CC. The highest enantiomeric excesses, similar to those obtained in the homogeneous phase, were achieved using silica as support or with the homogeneous tetra-tert-butyl salen catalyst dissolved in an imidazolium ionic liquid. The use of silica as support permits an easier separation and reuse of the catalyst from the reaction media.     

Oxygen‐Promoted Suzuki–Miyaura Reaction for Efficient Construction of Biaryls

As one of the most powerful and versatile methods for the construction of carbon–carbon bonds, the Suzuki–Miyaura cross‐coupling reaction has attracted great attention over the past three decades. In recent years, a huge amount of interest has been focused on the development of ligand‐free Suzuki–Miyaura reaction systems, which have the advantages of low cost, mild reaction conditions, and easy operation. So far, a number of ligand‐free Suzuki–Miyaura reaction systems have been developed by using simple palladium salts, nanopalladium, or supported palladium catalysts. In this account, we will review our recent research on the oxygen‐promoted ligand‐free Suzuki–Miyaura reaction. Interestingly, the oxygen‐promoting effect has been observed in different reaction media, including polyethylene glycol, organic/water mixed solvents and pure water. The oxygen‐promoted reaction systems demonstrate high efficiency for the construction of biaryls.

     

The use of palladium complexes in highly selective multistep organic synthesis

Palladium complexes are versatile catalysts for the selective construction of organic molecules. The use of a model system containing a norbornyl-palladium bond stable toward -hydrogen elimination allows the formation of a variety of molecules. Carbon monoxide is a particularly advantageous building block in these multistep reactions, because it helps to induce the formation of various types of carbon-carbon bonds. Some palladium-catalyzed multistep reactions, which proceed in sequence and have a common initial step,i.e., oxidative addition, are described.This review is based on material from a report delivered at the conference INEOS-94: The Modern Problems of Organometallic Chemistry (May 21–27, 1994, Moscow).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 412–420, March, 1995.     

Computational studies of cinchona alkaloid-catalyzed asymmetric Michael additions

Cinchona alkaloids exhibit remarkable catalytic activities in a wide range of organic transformations. This review summarizes the recent advances of computational studies in understanding the mechanism and origins of enantioselectivities in cinchona alkaloid-catalyzed asymmetric Michael additions. Key activation model and controlling factors of reactivity and selectivity are elucidated.     

Recent Developments and Optimization of Lipase‐Catalyzed Lactone Formation and Ring‐Opening Polymerization

To obtain materials useful for the biomedical field, toxic catalysts should be removed from the synthetic route of polymerization reactions and of their precursors. Lipase‐catalyzed ring‐opening polymerization and the synthesis of cyclic precursors can be performed with the same catalyst under different conditions. Here, we highlight the use of lipases as catalysts and optimization of their performance for both ring‐closing and ring‐opening polymerization, via varying parameters such as ring size, concentration, substrate molar ratio, temperature, and solvent. While the conditions for ring‐closing reactions and ring‐opening polymerizations of small molecules, such as ε‐caprolactone, have been extensively explored using Candida antarctica lipase B (CALB), the optimization of macrocyclization, especially for more bulky substrates is surveyed here. Finally, recent methods and polymer architectures are summarized with an emphasis on new procedures for more sustainable chemistry, such as the use of ionic liquids as solvents and recycling of polyesters by enzymatic pathways.

     

Iron catalyzed CN bond formation

Diversely functionalized nitrogen-containing heteroaromatic building blocks, fine chemicals and active pharmaceutical or agrochemical ingredients are conveniently prepared via CN bond formation as the key step. Since beginning of the last decade, there has been a flurry of intense research in forging CN bonds using iron catalysts due to their low cost, high natural abundance and non-toxic nature. The present review offers an overview of CN bond forming reactions involving aryl, allyl, propargyl and unactivated alkyl electrophilic substrates with nitrogen nucleophiles via the regular cross coupling reactions catalyzed by iron. In the miscellaneous section, a set of novel transformations facilitated by iron are included as well.     

A Versatile Co(bisalen) Unit for Homogeneous and Heterogeneous Cooperative Catalysis in the Hydrolytic Kinetic Resolution of Epoxides

Bisalen—very cooperative : A novel styryl‐substituted, unsymmetrical bisalen is shown to be a versatile precursor to both soluble and insoluble cooperative catalysts for the hydrolytic kinetic resolution of epoxides. The unique bisalen motif ensures all catalysts derived from it have the necessary molecular‐level ligand pairing needed for cooperative bimetallic catalytic reactions (see scheme).

     

Post‐Synthesis Functionalization of (Meth)acrylate Based Monoliths via Electron Beam Triggered Graft Polymerization

Porous polymeric monoliths were prepared via electron beam triggered free radical polymerization of (meth)acrylates. Post‐synthesis functionalization of these supports was accomplished via electron beam initiated free radical graft polymerization of methacryloyl‐substituted NHC precursors. The grafted precursors were converted into the corresponding copper complexes. Cu‐loadings were between 1.3 mg · g⁻¹ and 1.5 mg · g⁻¹. These supported catalysts were used in selected CO hydrosilylation and cyanosilylation reactions using a continuous flow setup.

     

All Kinds of Reactivity: Recent Breakthroughs in Metal‐Catalyzed Alkyne Chemistry

Alkynes of reactions : Recent breakthroughs in metal‐catalyzed alkyne reactions, which expand the synthetic utility of alkynes, have been achieved. These approaches broaden the range of alkynes that are accessible by C? N and C? C bond‐forming reactions and demonstrate that the use of bifunctional heterobimetallic catalysts can lead to new reactivity and excellent enantioselectivity (see scheme).

     

Unimolecular chemistry of metastable dimethyl isophthalate radical cations

The MS/MS spectrum of the metastable molecular ions of dimethyl isophthalate 1 differs from that of the isomeric dimethyl terephthalate 2 by the observation of, inter alia, a quite intense loss of C,H₂,O ascribed to formaldehyde. Results obtained using a combination of mass spectrometry techniques suggest that this process could consist of an isomerization reaction of the molecular ion into an ion–neutral complex (INC) linking a benzoyl radical and neutral formaldehyde to a proton [ArCOHOCH₂]⁺. Within the complex, a proton transfer catalyzed by formaldehyde occurs resulting in the production of an ionized cyclohexadienylidene methanone (ketene) structure.     

Asymmetric Carbon–Carbon Bond Formation under Continuous‐Flow Conditions with Chiral Heterogeneous Catalysts

Catalytic asymmetric carbon–carbon bond‐forming reactions provide one of the most efficient ways to synthesize optically active compounds, and, accordingly, many chiral catalysts for these reactions have been developed in the past two decades. However, the efficiency of the catalysts in terms of turnover number (TON) is often lower than that of some other reactions, such as asymmetric hydrogenation, and this has been one of the obstacles for industrial applications. Although there are some difficulties in increasing the efficiency, the issues might be solved by using continuous flow in the presence of chiral heterogeneous catalysts. Indeed, continuous‐flow systems have several advantages over conventional batch systems. Here we summarize the recent progress in asymmetric C? C bond‐forming reactions under continuous‐flow conditions with chiral heterogeneous catalysts.     

Odyssey in Polyphasic Catalysis by Metal Nanoparticles

Nanometer‐sized metal particles constitute an unavoidable family of catalysts, combining the advantages of molecular complexes in regards to their catalytic performances and the ones of heterogeneous systems in terms of easy recycling. As part of this research, our group aims at designing well‐defined metal nanoparticles based‐catalysts, in non‐conventional media (ionic liquids or water), for various catalytic applications (hydrogenation, dehalogenation, carbon‐carbon coupling, asymmetric catalysis) in mild reaction conditions. In the drive towards a more eco‐responsible chemistry, the main focuses rely on the search of highly active and selective nanocatalysts, in association with an efficient recycling mainly under pure biphasic liquid‐liquid conditions. In this Personal Account, we proposed our almost fifteen‐years odyssey in the world of metal nanoparticles for a sustainable catalysis.

     

C−As Bond Formation Reactions for the Preparation of Organoarsenic(III) Compounds

Potential widespread applications of organoarsenic chemistry have been limited by the inherent lack of safe and effective As?C bond formation reactions. Several alternative reagents and methods have been developed in the last few decades to address the hazards and drawbacks associated with traditional arsenic synthetic strategies. Herein, this minireview summarizes the advances made in nucleophilic, electrophilic, radical and metal‐mediated As(III)?C bond formations while specifically highlighting the behavior of arsenic synthons with various well‐established reagents (eg. Grignard reagents, organolithium compounds, organometallic reagents, radical initiators and Lewis/Brønsted bases). Avenues for asymmetric synthesis are also discussed, as are recent advances in organoarsenic chemistry suggesting that arsines exhibit novel reactivities independent from that of other relatively more well explored Group V cogeners.     

Palladium‐Catalyzed Carbon–Carbon Bond Formation and Cleavage of Organo(hydro)fullerenes

Palladium can tailor fullerenes : Palladium catalysts enable a number of C? H bond transformations of organo(hydro)fullerene. In addition to anticipated coupling reactions (C? H bond allylation and arylation), an unexpected new C? H bond dimerization reaction and C? C bond‐cleavage reaction were also uncovered.

     

Cover Picture: Recent Advances in Transition Metal‐Catalyzed Asymmetric Radical Reactions (Chin. J. Chem. 3/2018)

The control of stereoselectivity in radical reactions is of great importance, but remains a formidable challenge. The cover picture shows that the enantiomerically pure compounds can be prepared in radical transformations using chiral transition metal complexes as catalysts. Recent advances are summarized in the review by Kong et al. on page 247–256.