Olefin Bifunctionalization: A Visible‐light Photoredox‐catalyzed Aryl Alkoxylation of Olefins

Olefin bifunctionalization is a facile route to obtain complex molecules from abundant and commercially available olefin feedstocks. Visible light together with a catalytic amount of tris(bipyridine)ruthenium salt catalyzes the aryl alkoxylation of styrenes with aryl diazonium salts in alcohol solvents via a photoredox process. The scope of this proposed reaction with respect to various aryl diazonium salts and styrenes has been investigated.     

Organoselenium‐Catalyzed Regioselective C−H Pyridination of 1,3‐Dienes and Alkenes

An efficient approach for organoselenium‐catalyzed regioselective C−H pyridination of 1,3‐dienes to form pyridinium salts has been developed. This method was also successfully applied to direct C−H pyridination of alkenes. Fluoropyridinium reagents, or initially loaded pyridine derivatives, acted as pyridine sources in the pyridination reactions. The obtained pyridinium salts could be further converted under different conditions. This work is the first example of catalytic C‐2 direct C−H functionalization of 1,3‐dienes and the first case of organoselenium‐catalyzed C−H pyridination.     

Chiral Tertiary Sulfonium Salts as Effective Catalysts for Asymmetric Base‐Free Neutral Phase‐Transfer Reactions

Although chiral quaternary ammonium and phosphonium salts are commonly used for asymmetric organocatalysis, the catalytic ability of chiral tertiary sulfonium salts has yet to be demonstrated in asymmetric synthesis. Herein, we show that chiral bifunctional trialkylsulfonium salts catalyze highly enantioselective conjugate additions of 3‐substituted oxindoles to maleimides under base‐free neutral phase‐transfer conditions.     

Crystal structure of meso‐substituted pyrazolyl porphyrin complexes and their highly active catalyst for oxidation of alkylbenzenes

During the past few years, a great deal of effort has been devoted to the anchoring of catalytic oxidation. In this work, three new catalysts CuPp, MnPp and ZnPp by solvothermal methods with 5, 10, 15, 20‐tetrakis(4‐N‐pyrazolyl)‐phenyl porphyrin (H₂Pp) and the corresponding metal salts have been synthesized and structurally characterized. The single crystal structures determined by X‐ray diffraction show the bond distances of M‐N in porphyrin cores determined the conformation of porphyrin rings. We explored the catalytic activity of CoPp, CuPp, MnPp and ZnPp for oxidation of alkylbenzenes. The experimental results display these products exhibit high catalytic activities and selectivities for oxidation of ethylbenzene to acetophenone, and can be reused by filtration without appreciable decrease in catalytic activity and selectivity.     

Supramolecular Synthons in Designing Low Molecular Mass Gelling Agents: L‐Amino Acid Methyl Ester Cinnamate Salts and their Anti‐Solvent‐Induced Instant Gelation

Easy access to a class of chiral gelators has been achieved by exploiting primary ammonium monocarboxylate ( PAM ), a supramolecular synthon. A combinatorial library comprising of 16 salts, derived from 5 l ‐amino acid methyl esters and 4 cinnamic acid derivatives, has been prepared and scanned for gelation. Remarkably, 14 out of 16 salts prepared (87.5 % of the salts) show moderate to good gelation abilities with various solvents, including commercial fuels, such as petrol. Anti‐solvent induced instant gelation at room temperature has been achieved in all the gelator salts, indicating that the gelation process is indeed an aborted crystallization phenomenon. Rheology, optical and scanning electron microscopy, small angle neutron scattering, and X‐ray powder diffraction have been used to characterize the gels. A structure‐property correlation has been attempted, based on these data, in addition to the single‐crystal structures of 5 gelator salts. Analysis of the FT‐IR and ¹H NMR spectroscopy data reveals that some of these salts can be used as supramolecular containers for the slow release of certain pest sex pheromones. The present study clearly demonstrates the merit of crystal engineering and the supramolecular synthon approach in designing new materials with multiple properties.     

Interrupted Imino‐Nazarov Cyclization of 1‐Aminopentadienyl Cation and Related Cascade Process

Facile 4π conrotatory imino‐Nazarov cyclization of a 1‐aminopentadienyl cation generated from condensation an aldehyde and secondary aniline in the presence of a catalytic amount of a Lewis acid has been developed. Silver(I)‐catalyzed intramolecular arene trapping of the resulting cyclic oxyallyl cation leads to formation of tricyclic indoline‐fused cyclopentanone. The use of lanthanide salts allows transformation after the initial trapping to afford tetrahydroquinoline‐fused cyclopentenone in a concise manner.     

Highly efficient bimetallic iron‐palladium catalyzed Michael‐type Friedel–Crafts reactions of indoles with chalcones

Iron–palladium is a superior bimetallic catalyst in the presence of acetylacetone (Acac) with remarkable synergistic effect for the Michael‐type Friedel–Crafts reactions of indoles with chalcones. This catalytic system has the advantages of mild reaction conditions, smaller amount of metal salts, high yields of the desired products and operational simplicity, which make it a useful and promising process for the synthesis of indole derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Palladium N‐heterocyclic‐carbene‐catalyzed ortho‐arylation of benzaldehyde derivatives

New, sterically demanding 1,3‐dialkylbenzimidazolium salts ( 2a–c ) as N‐heterocyclic‐carbene precursors have been synthesized and characterized. The ortho position of aromatic aldehydes was directly and selectively arylated with aryl chlorides in the presence of a catalytic system prepared in situ from Pd(OAc)₂, 1,3‐dialkylbenzimidazolium chlorides ( 2a–c ), and Cs₂CO₃. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:569–574, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20479     

Visible‐Light‐Driven Iron‐Promoted Thiocarboxylation of Styrenes and Acrylates with CO2

The first thiocarboxylation of styrenes and acrylates with CO₂ was realized by using visible light as a driving force and catalytic iron salts as promoters. A variety of important β‐thioacids were obtained in high yields. This multicomponent reaction proceeds in an atom‐ and redox‐economical manner with broad substrate scope under mild reaction conditions. Notably, high regio‐, chemo‐, and diasteroselectivity are observed. Mechanistic studies indicate that a radical pathway can account for the unusual regioselectivity.     

Iridium‐Catalyzed Selective Cross‐Coupling of Ethylene Glycol and Methanol to Lactic Acid

An atom‐economic approach that has an unprecedented high selectivity for the synthesis of lactic acid (LA) based on a catalytic dehydrogenative cross‐coupling by using inexpensive bulk ethylene glycol and methanol is described. This method relies on the synthesis and utilization of a novel iridium catalyst bearing three N‐heterocyclic carbenes derived from 1,3‐dimethylbenzimidazolium salts, and exhibits outstanding activity in the production of LA [turnover frequency (TOF) up to 3660 h^?1] owing to an elegant metal–ligand cooperation.     

One‐Pot C−H Functionalization of Arenes by Diaryliodonium Salts

A transition‐metal‐free, mild, and highly regioselective synthesis of nitroarenes from arenes has been developed. The products are obtained in a sequential one‐pot reaction by nitration of iodine(III) reagents with two carbon ligands, which are formed in situ from iodine(I). This novel concept has been extended to formation of aryl azides, and constitutes an important step towards catalytic reactions with these hypervalent iodine reagents. An efficient nitration of isolated diaryliodonium salts has also been developed, and the mechanism is proposed to proceed by a [2,2] ligand coupling pathway.     

A Simple and Efficient Synthesis of Ethyl 1‐Aryl‐4‐formyl‐1H‐pyrazole‐3‐carboxylates

A new simple and convenient method of synthesis of ethyl 1‐aryl‐4‐formyl‐1H‐pyrazole‐3‐carboxylates from aromatic amines via diazonium salts has been developed. Hydrolysis and hydrazinolyization of these compounds has been investigated.     

Colloidal Noble‐Metal and Bimetallic Alloy Nanocrystals: A General Synthetic Method and Their Catalytic Hydrogenation Properties

A general single‐step strategy has been developed for the direct thermal decomposition of noble‐metal salts in octadecylamine to synthesize octahedron‐ and rod‐shaped noble‐metal aggregates and monodisperse noble‐metal or bimetallic alloy nanocrystals without introducing any additive into the system. It has presented a facile and economic way to fabricate these nanocrystals, especially alloy nanocrystals, which does not require a post‐synthesis solid‐state annealing process. The morphology of the nanocrystals can be easily controlled by tuning the synthetic temperature. Their ability to catalyze heterogeneous Suzuki coupling reactions has been investigated and showed satisfactory catalytic activity. The catalytic performance of the monometallic and bimetallic alloy nanocrystals were also evaluated in the selective hydrogenation of citral in a conventional organic solvent (toluene) and a green solvent (supercritical carbon dioxide, scCO₂). Interestingly, the catalysts performed differently to each other when they were in scCO₂ owing to the different morphology, which should be readily optimized for further use.     

4‐Nitro‐3‐(5‐tetrazole)furoxan and Its Salts: Synthesis,Characterization, and Energetic Properties

A series of new energetic salts based on 4‐nitro‐3‐(5‐tetrazole)furoxan (HTNF) has been synthesized. All of the salts have been fully characterized by nuclear magnetic resonance (¹H and ¹³C), infrared (IR) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of neutral HTNF ( 3 ) and its ammonium ( 4 ) and N‐carbamoylguanidinium salts ( 9 ) have been determined by single‐crystal X‐ray diffraction analysis. The densities of 3 and its nine salts were found to range from 1.63 to 1.84 g cm^?3. Impact sensitivities have been determined by hammer tests, and the results ranged from 2 J (very sensitive) to >40 J (insensitive). Theoretical performance calculations (Gaussian 03 and EXPLO 5.05) provided detonation pressures and velocities for the ionic compounds 4 – 12 in the ranges 25.5–36.2 GPa and 7934–8919 m s^?1, respectively, which make them competitive energetic materials.     

Asymmetric Organocatalysis: The Emerging Utility of α,β‐Unsaturated Acylammonium Salts

Although acylammonium salts are well‐studied, chiral α,β‐unsaturated acylammonium salts have received much less attention. While these intermediates are convenient synthons, which are readily available from several commodity unsaturated acids and acid chlorides, and possess three reactive sites, their application in organic synthesis has been limited because of the lack of appropriate chiral Lewis bases for their generation. In recent years, the utility of chiral, unsaturated acylammonium salts has expanded considerably, thus demonstrating the unique reactivity of this intermediate leading to the development of a diverse array of catalytic, asymmetric transformations including organocascade processes. This Minireview highlights the recent and growing interest in these intermediates which might spark further research into their untapped potential for asymmetric organocascade catalysis. A cursory comparison is made to related unsaturated iminium and acylazolium intermediates.     

Effect of Sodium Cation on Metallacycle β‐Hydride Elimination in CO2–Ethylene Coupling to Acrylates

The catalytic conversion of carbon dioxide and olefins into acrylates has been a long standing target, because society attempts to synthesize commodity chemicals in a more economical and sustainable fashion. Although nickel complexes have been known to successfully couple CO₂ and ethylene for decades, a key β‐hydride elimination step has proven a major obstacle to the development of a catalytic process. Recent studies have shown that Lewis acid additives can be used to create a lower‐energy pathway for β‐hydride elimination and facilitate a low number of catalytic turnovers. However, the exact manner, in which the Lewis acid promotes β‐hydride elimination remains to be elucidated. Herein, we describe the kinetic and thermodynamic role that commercially relevant and weakly Lewis acidic sodium salts play in promoting β‐hydride elimination from nickelalactones synthesized from CO₂ and ethylene. This process is compared to a non‐Lewis acid promoted pathway, and DFT calculations were used to identify differences between the two systems. The sodium‐free isomerization reaction gave a rare CO₂‐derived β‐nickelalactone complex, which was structurally characterized.     

Nickel‐Catalyzed Cyclization of ortho‐Iodoketoximes and ortho‐Iodoketimines with Alkynes: Synthesis of Highly Substituted Isoquinolines and Isoquinolinium Salts

A convenient method for the synthesis of highly substituted isoquinolines and isoquinolinium salts by the nickel‐catalyzed cyclization of ortho‐haloketoximes and ‐ketimines, respectively, with alkynes is described. The reaction of ortho‐haloketoximes and various alkynes in the presence of [Ni(PPh₃)₂Br₂] and zinc powder in a mixture of acetonitrile and tetrahydrofuran at 80 °C for 15 hours gave 1,3,4‐trisubstituted isoquinoline products in moderate to excellent yields and high regioselectivity. The corresponding isoquinoline N‐oxide was found to be the intermediate in the cyclization reaction pathway. In contrast, the reaction of ortho‐haloketimines and alkynes under similar catalytic conditions in tetrahydrofuran at 70 °C for two hours gave 1,2,3,4‐tetrasubstituted isoquinolinium salts in good to excellent yields.     

1,1,3,3‐Tetratriflylpropene (TTP): A Strong,Allylic C–H Acid for Brønsted and Lewis Acid Catalysis

Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic C–H acid for Brønsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, Hosomi–Sakurai, and Friedel–Crafts acylation reactions. X‐ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP.     

Iridium‐Catalyzed ortho‐Arylation of Benzoic Acids with Arenediazonium Salts

In the presence of catalytic [{IrCp*Cl₂}₂] and Ag₂CO₃, Li₂CO₃ as the base, and acetone as the solvent, benzoic acids react with arenediazonium salts to give the corresponding diaryl‐2‐carboxylates under mild conditions. This C? H arylation process is generally applicable to diversely substituted substrates, ranging from extremely electron‐rich to electron‐poor derivatives. The carboxylate directing group is widely available and can be removed tracelessly or employed for further derivatization. Orthogonality to halide‐based cross‐couplings is achieved by the use of diazonium salts, which can be coupled even in the presence of iodo substituents.     

Convenient synthesis of 1,2,3,4‐tetrahydro‐pyrimidin‐5‐ylbenzoxazoles

2‐Pyrimidin‐5‐ylbenzoxazoles 7 have been synthesized by condensation of 5‐pyrimidinecarboxaldehyde 4 with substituted aminophenols 5 followed by oxidative cyclization of the resulting Schiff's bases 6 with iodobenzene diacetate. Subsequent formation of methylpyrimidinium salts 8 and reduction thereafter afforded tetrahydropyrimidinylbenzoxazoles 10. This method has been utilized in the synthesis of M₁ muscarinic agonist candidates.