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We have developed the divergent deaminative borylation and hydrodeamination of primary aromatic amines using bis(pinacolato)diboron. These transformations can be switched by the reaction conditions. Mechanistic and computational studies have suggested that the cleavage of the C-N bond and the formation of C-B bond are unlikely to involve free aryl radical intermediates. However, hydrodeamination is shown to proceed via hydrogen atom transfer between the corresponding aryl radical and an ethereal solvent.

Pyrene is one of the most attractive polycyclic aromatic hydrocarbons (PAHs) in photochemistry. Based on their redox properties, pyrenes have potential as photosensitizers. In this review, we summarize recent developments in pyrene-catalyzed photoinduced organic reactions occurring via energy transfer or single-electron transfer based on the excited state of the pyrene.1 Introduction2 Photolysis Involving N–O Bond Cleavage or Decarboxylation3 (Cyclo)addition Reactions with Styrenes4 Transformations via Cleavage of C–F, C–I, C–S and C–N Bonds5 Reactions Based on Sensitization-Initiated Electron Transfer (SenI­-ET)6 Miscellaneous Transformations7 Conclusion

A new synthetic method for preparing fluorenes from amino group-containing biaryls and Meldrum's acid derivatives was developed. The reaction proceeded without a catalyst and loss of functional groups. The corresponding six- and seven-membered cyclic products were obtained using biaryl ether and

Herein, direct unreactive C-N borylation of aromatic amines by a photocatalyst was achieved. The C-N borylation of aromatic amines with bis(pinacolato)diboron (B2pin2) proceeded using a pyrene catalyst under light irradiation to afford desired borylated products and aminoborane as a byproduct. The yield of the borylated product improved under a CO2 atmosphere which probably reduced the inhibitory effect of aminoborane. Mechanistic studies suggested that the C-N bond cleavage and C-B bond formation proceeded via a concerted pathway.

A simple gold‐catalyzed annulation of 1,8‐dialkynylnaphthalenes utilizing a cationic gold catalyst was developed. Such a peri‐position of two alkynyl substituents has not been studied in gold catalysis before. Dependent on the substrate, the reactions either follow a mechanism involving vinyl cation intermediates or involve a dual gold catalysis mechanism which in an initial 6‐endo‐dig‐cyclization generates gold(I) vinylidene intermediates that are able to insert into C−H bonds. Indenophenalene derivatives were obtained in moderate to high yields. In addition, the bidirectional gold‐catalyzed annulation of tetraynes provided even larger conjugated π‐systems. The optoelectronic properties of the products were also investigated., The 6‐endo‐cyclization of the first diyne unit (blue) with two alkynes in peri‐position induces a switch to a 5‐exo‐cyclization for the second peri‐diyne unit (red) in the fast modular synthesis of new extended π‐systems.

Often stoichiometric amounts of gold find use in materials science; occasionally gold is even used as a support. This review discusses the contributions of gold catalysis, both homogeneous and heterogeneous, to the field of materials science. One topic is the synthesis of polymers, including nanowires and polyesters, the postcyclization of polymers, polymerization by cyclopropanation, and gold-catalyzed radical polymerization reactions. Other topics are dyes, phosphonium salts, and a wide range of extended conjugated π-systems, the latter ranging from acenes, pentalene derivatives, and different heterocyclic π-systems to fascinating applications in the synthesis of helical anellated aromatic molecules. The existing contributions clearly demonstrate the potential of gold catalysis for significant future impulses for the field of materials science.

The direct access to dimethoxymethane (DMM) from CO2/H2 in MeOH is an attractive approach, but more active, selective, and robust catalyst systems are still desirable for an application of this system. Herein, we present the performance enhancing effect of additives on ruthenium-triphos catalyst systems for CO2 hydrogenation to DMM. In the presence of PPh3, functioning as both additional ligand and precursor for Lewis-acidic phosphonium salts, increased turnover numbers for DMM are achieved. Moreover, PPh3 significantly diminishes catalyst degradation via carbonylation to cationic [RuH(CO)2(triphos)]OTf, which remains an active species in the synthesis of DMM. Catalyst recycling over up to five runs with minimal loss in catalyst performance underlines the robustness of the system. Both, the recyclability of the system and the suppression of catalyst deactivation pathways encourage for application in sustainable continuous processes.

We synthesised novel hexacoordinated organosilicon compounds with two 2-(2-pyridyl)phenyl groups. Single-crystal X-ray structure analyses indicated that Lewis acid-base interactions exist between the silicon atom and two nitrogen atoms of the pyridine rings, and that hexacoordinated organosilicon compounds have slightly distorted octahedral structures in the solid state. The hexacoordinated organosilicon compounds are stable in air, water, heat, acids, and bases. The fluorescent quantum yield increased dramatically and a significant red-shift of the maximum fluorescence wavelength was observed with the introduction of amino groups on the 2-(2-pyridyl)phenyl aromatic rings. The fluorescence colours of a hexacoordinated organosilicon compound with two amino groups can be switched by protonation and deprotonation (neutralisation) of the amino groups.

Precise control of the selectivity in organic synthesis is important to access the desired molecules. We demonstrate a regiospecific annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene derivatives for a geometry‐controlled synthesis of linear bispentalenes, which is one of the promising structures for material science. A gold‐catalyzed annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene could produce two isomeric pentalenes, but both electronic and steric effects on the aromatics at the terminal position of the alkyne prove to be crucial for the selectivity; especially a regiospecific annulation was achieved with sterically blocked substituents; namely, 2,4,6‐trimetyl benzene or 2,4‐dimethyl benzene. This approach enables the geometrically controlled synthesis of linear bispentalenes from 1,2,4,5‐tetraethynylbenzene or 2,3,6,7‐tetraethynylnaphthalene. Moreover, the annulation of a series of tetraynes with a different substitution pattern regioselectively provided the bispentalene scaffolds. A computational study revealed that this is the result of a kinetic control induced by the bulky NHC ligands., Give me five: The regiospecific annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene derivatives is reported. Both electronic and steric effects on the aromatic moieties of the substrates are crucial for the selectivity. Moreover, the annulation of a series of differently substituted tetraynes regioselectively provided the corresponding bispentalenes (see scheme). The selectivity of this transformation is rationalized by computational studies, and the opto‐electronic properties of the obtained bispentalene derivatives are also reported.

[Au2(μ-dppm)2]Cl2-mediated photocatalysis reactions are usually initiated by ultraviolet A (UVA) light; herein, an unreported system using blue light-emitting diodes (LEDs) as excitation light sour...

Herein we report a highly selective photoredox C(sp3 )-H alkylation/arylation of ethers through the combination of a photo-organocatalyst (benzaldehyde) and a transition-metal catalyst (nickel). This method provides a simple and general strategy for the C(sp3 )-H alkylation/arylation of ethers. A selective late-stage modification of (-)-ambroxide has also been conducted to demonstrate the applicability of the method.

The solubilizing side-groups of solution-processable π-conjugated organic semiconductors affect both the crystal structure and microstructure of the respective thin films and thus charge-carrier mobility in devices. In this work, we explore how the alkyl side-chain length influences thin-film structure and charge transport in field-effect transistors of zone-cast, naphthalene-based bispentalenes. By tuning the alkyl-chain length and the casting speed, we alter the microstructure from highly aligned ribbons, to feathered ribbons, to disordered grains. Concurrently, the hole mobility changes over two orders of magnitude, from 0.001 cm2 V−1 s−1 at the fastest speeds to roughly 0.1 cm2 V−1 s−1 at slower speeds. The highest mobilities correspond to the presence of an aligned ribbon morphology. While optical measurements indicate negligible electronic differences between the molecules, grazing incidence X-ray diffraction measurements show that the films display different degrees of order and alignment. The compound with pentyl side-chains exhibits the largest tolerance to different processing conditions, yielding an aligned ribbon microstructure and high mobility over a wide range of casting speeds. Our results highlight the impact that even small changes to the molecular structure can have on the processing window and transport properties of thin-film devices.

Herein, direct unreactive C-N borylation of aromatic amines by a photocatalyst was achieved. The C-N borylation of aromatic amines with bis(pinacolato)diboron (B

Herein, direct unactivated C-N borylation of aromatic amines by a photocatalyst was achieved under mild and metal-free conditions. The C-N borylation of aromatic amines with bis(pinacolato)diboron (B2pin2) proceeded in the presence of a pyrene catalyst under light irradiation (λ = 365 nm) to afford desired borylated products and aminoborane as a byproduct. The yield of borylated product improved under a CO2 atmosphere. Reactions conducted in the presence of a stoichiometric amount of aminoborane under N2 or CO2 indicated that CO2 reduced the inhibitory effect of aminoborane. Optimal reaction conditions were applied to a variety of aromatic amines. Mechanistic studies suggested that the C-N bond cleavage and C-B bond formation proceeded via a concerted pathway.

Organoboron compounds are versatile synthetic building blocks. We herein report a new strategy, a photochemical gold-catalyzed chemo-selective Hiyama arylation of B,Si bifunctionalized reagents with diazonium salts, which is orthogonal to common strategies and therefore a unique tool for synthesis of valuable biarylboronates. With this new methodology a wide array of diversely functionalized sp2 - and sp3 -hybridized biarylboronates were obtained. Notably, the synergism of gold catalysis with copper catalysis or palladium catalysis, allows for one-pot iterative C-X (heteroatom) and C-C couplings for the rapid assembly of several simple fragments to relatively complex molecules. Mechanistic studies indicated that photosensitizer-free conditions were superior to gold/Ru(bpy)3 Cl2 dual catalysis.

The gold-catalyzed annulation of diethynyl N-heterocycles for the synthesis of quinoxaline-/phenazine-based pentalenes and the study of their optoelectronic properties are described. The inhibition of the gold catalyst by the nitrogen centers in the substrate and the product could be overcome by increasing the reaction temperature to 130 °C, which usually leads to catalyst decomposition in gold catalysis. At 130 °C, 6,7-di(arylethynyl)quinoxalines in chlorobenzene give the corresponding pentalenes. The annulation of 2,3-di(arylethynyl)quinoxalines requires an even higher temperature under microwave irradiation. The quinoxaline-based pentalenes showed lower LUMO levels compared to the corresponding naphthalene-based pentalenes.

In this report, hydroxymethylfurfural (HMF) is used as a bio-based feedstock for homogeneous metal-catalysed hydrogenation. Several ligand classes and metals are employed to reduce the aldehyde and aromatic ring of HMF. The previously unknown homogeneous catalysed hydrogenation of HMF to tetrahydrofuran-dimethanol (THFDM) was investigated using different catalyst systems. NHCs and phosphites give higher trans/cis ratios (between 1 : 1.25 and 1 : 3.95) of the product THFDM, but low conversions of only up to 17% accompanied by up to 92% yield of bis(hydroxymethyl)furan at 10 bar H2 and 120 °C. Conversely, di-phosphine ligated ruthenium catalysts in up to 87% yield lead to the highest overall conversion but only moderate trans/cis ratios of only 1 : 3.1–1 : 5.

Highly substituted 2-cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis-acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2-cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.

The current development on gold catalysts in the context of carbon dioxide transformation is summarized.

The scope of photosensitizer-free visible light-driven gold-catalyzed cross-coupling was evaluated by a wide variety of organoboron and organosilicon species using four equivalents of aryldiazonium salts and (4-CF3-C6H4)3PAuCl in MeOH. In addition, a C(sp or sp2)–C(sp2) cross-coupling of organotrimethylsilanes and aryldiazonium salts was investigated. The reactions can be conducted under very mild reaction conditions, with a reduced amount of aryldiazonium salt (1.2 equiv.) by using a catalytic amount of Ph3PAuNTf2 in MeCN under irradiation with blue LEDs at room temperature.

The synthesis of silafluorene derivatives from aminobiphenyl compounds and dihydrosilanes via a double sila-Friedel–Crafts reaction using a borane catalyst has been achieved. This method is applicable to the synthesis of a variety of silafluorene derivatives, such as multisubstituted silafluorenes, spirosilabifluorenes, and silicon-bridged terphenyl compounds, which are not readily obtained using conventional synthetic methods. In addition, we have demonstrated the transformation of the amino groups in these silafluorene derivatives into other substituents.

The metal-free reactions of 2H-azirines with C,N-cyclic azomethine imines were investigated. N-Bridged strained ring-fused triazole derivatives or 1,2,4-triazine derivatives are obtained, and the chemoselectivity is dependent on the protecting group on the azomethine dipole. Although benzoyl-protected starting materials give access to strained polycyclic compounds, a ring-opening occurs in the case of a tosyl protecting group that is cleaved during the process with elimination of sulfinic acid. 1,2,4-Triazine can be prepared on a mmol-scale and concomitantly oxidized with air as an oxidant to form the corresponding ketone, which is an interesting structural motif that can be found in bioactive scaffolds.

Silver-catalyzed reactions are some of the important methodologies in organic chemistry. Since 2007, a new application of silver catalysts has been emerging. For the sequential carboxylation and cyclization of alkyne derivatives, such as propargyl alcohols and amines, using carbon dioxide, silver catalysts show significant reactivity under mild conditions unlike other transition metals. These developments have received much attention for the effective utilization of carbon dioxide in organic chemistry to synthesize heterocyclic compounds. Related silver-catalyzed C-C bond forming reactions with carbon dioxide have also provided the synthetic methods of the corresponding carboxylic acid derivatives. In this review, the recent studies of the silver-catalyzed carboxylation reactions using carbon dioxide are described.

The scope of photosensitizer-free visible light-driven gold-catalyzed cross-coupling was evaluated by a wide variety of organoboron and organosilicon species using four equivalents of aryldiazonium salts and (4-CF3-C6H4)3PAuCl in MeOH. In addition, a C(sp or sp2)-C(sp2) cross-coupling of organotrimethylsilanes and aryldiazonium salts was investigated. The reactions can be conducted under very mild reaction conditions, with a reduced amount of aryldiazonium salt (1.2 equiv.) by using a catalytic amount of Ph3PAuNTf2 in MeCN under irradiation with blue LEDs at room temperature.

The gold-catalyzed facile synthesis of U-shaped and S-shaped bispentalenes is described from easily available tetra(arylethynyl)-benzenes and -naphthalenes. The optoelectronic and transistor properties were also investigated. The selectivity between the U-shaped and S-shaped bispentalene isomers can be tuned by the bulkiness of the ligand and the substrates. The S-shaped naphthalene-based bispentalene shows a one-dimensional face-to-face packing pattern in solid state and a good hole mobility, indicating that the S-shaped bispentalene core is highly suitable for transistor applications. The gold-catalyzed annulation of tetraynes provides a useful protocol in the synthesis of bispentalenes for organic semiconductors.

While gold-mediated synergistic catalytic processes involving transmetalations with other metals are well understood, AuI /AuIII cycles in these reactions are rarely reported. Herein a gold-catalyzed direct alkynylation of cyclopropenes is enabled by two operating catalytic cycles, an oxidative catalytic cycle involving an alkynyl AuIII complex formed by oxidative addition and one involving a silver-mediated C-H activation.

Herein we report a highly selective photoredox C(sp

We describe a novel, short, and flexible approach to diverse N-doped polycyclic aromatic hydrocarbons (PAHs) through gold-catalyzed π-extension of anthranils with o-ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional-group compatibility as well as scale-up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C-H annulation/protodeauration sequence terminated by a Friedel-Crafts-type cyclization. Photophysical studies of the products indicated violet-blue fluorescence emission with quantum yields up to 0.45.

C-C bond-forming carboxylation and cyclization of trimethyl(2-methylenebut-3-yn-1-yl)silane derivatives and carbon dioxide was developed. Silver catalysts and CsF promoted the reaction to afford the corresponding 2-furanone and 2-pyrone derivatives in good-to-high yields. The structure of the 2-furanone was confirmed by single-crystal X-ray crystallography, which revealed that the geometry of the exo-olefin was that of a Z-isomer. When an aromatic ring-substituted alkyne was used, 2-furanone derivatives were selectively obtained via 5-exo-dig cyclization, whereas the reaction of alkyl-substituted alkynes produced 2-pyrone derivatives with high selectivity.

Highly Z-selective syntheses of oxazolidin-2-ones from propargylic alcohols containing internal alkynes and phenyl isocyanate were achieved by using a combination of silver acetate and N,N-dimethylaminopyridine. The catalytic system was applied to propargylic alcohols containing alkyl-substituted alkyne groups. By considering the results in the presence and absence of an electron-withdrawing group on the aromatics, it was shown that the silver catalyst effectively activates the C≡C triple bond by acting as a π-Lewis acid to produce the corresponding oxazolidinones with high Z-selectivities.

The stereoselective synthesis of (E)-bromovinyloxazolidinones was developed by the three-component reaction of propargylic amines, carbon dioxide, and N-bromosuccinimide in the presence of a silver...

Silver-catalyzed reactions are some of the important methodologies in organic chemistry. Since 2007, a new application of silver catalysts has been emerging. For the sequential carboxylation and cyclization of alkyne derivatives, such as propargyl alcohols and amines, using carbon dioxide, silver catalysts show significant reactivity under mild conditions unlike other transition metals. These developments have received much attention for the effective utilization of carbon dioxide in organic chemistry to synthesize heterocyclic compounds. Related silver-catalyzed C–C bond forming reactions with carbon dioxide have also provided the synthetic methods of the corresponding carboxylic acid derivatives. In this review, the recent studies of the silver-catalyzed carboxylation reactions using carbon dioxide are described.

The stereoselective synthesis of (E)-bromovinyloxazolidinones was developed by the three-component reaction of propargylic amines, carbon dioxide, and N-bromosuccinimide in the presence of a silver...

Highly Z-selective syntheses of oxazolidin-2-ones from propargylic alcohols containing internal alkynes and phenyl isocyanate were achieved by using a combination of silver acetate and N,N-dimethylaminopyridine. The catalytic system was applied to propargylic alcohols containing alkyl-substituted alkyne groups. By considering the results in the presence and absence of an electron-withdrawing group on the aromatics, it was shown that the silver catalyst effectively activates the C≡C triple bond by acting as a π-Lewis acid to produce the corresponding oxazolidinones with high Z-selectivities.

A catalytic amount of silver benzoate with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) was an effective catalytic system for the reaction of carbon dioxide with various ketones containing an alkyne group at an appropriate position. These reactions afforded the corresponding γ-lactone derivatives in good to high yields under mild conditions.

A silver/DBU catalyst system was developed for the effective synthesis of cyclic carbonate and oxazolidinone from the reaction of CO2 with propargylic alcohols and propargylic amines, respectively,...

Organic contaminants adsorbed on the surface of titanium dioxide (TiO2) can be decomposed by photocatalysis under ultraviolet (UV) light. Here we describe a novel protocol employing the TiO2 photocatalysis to locally alter cell affinity of the substrate surface. For this experiment, a thin TiO2 film was sputter-coated on a glass coverslip, and the TiO2 surface was subsequently modified with an organosilane monolayer derived from octadecyltrichlorosilane (OTS), which inhibits cell adhesion. The sample was immersed in a cell culture medium, and focused UV light was irradiated to an octagonal region. When a neuronal cell line PC12 cells were plated on the sample, cells adhered only on the UV-irradiated area. We further show that this surface modification can also be performed in situ, i.e., even when cells are growing on the substrate. Proper modification of the surface required an extracellular matrix protein collagen to be present in the medium at the time of UV irradiation. The technique presented here can potentially be employed in patterning multiple cell types for constructing coculture systems or to arbitrarily manipulate cells under culture.

We demonstrate a novel application of TiO2 photocatalysis for modifying the cell affinity of a scaffold surface in a cell-culture environment. An as-deposited octadecyltrichlorosilane self-assembled monolayer (OTS SAM) on TiO2 was found to be hydrophobic and stably adsorbed serum albumins that blocked subsequent adsorption of other proteins and cells. Upon irradiation of ultraviolet (UV) light, OTS molecules were decomposed and became permissive to the adhesion of PC12 cells via adsorption of an extracellular matrix protein, collagen. Optimal UV dose was 200 J cm(-2) for OTS SAM on TiO2. The amount of collagen adsorption decreased when excessive UV light was irradiated, most likely due to the surface being too hydrophilic to support its adsorption. This UV-induced modification required TiO2 to be present under the SAM and hence is a result of TiO2 photocatalysis. The UV irradiation for surface modification can be performed before cell plating or during cell culture. We also demonstrate that poly(ethylene glycol) SAM can also be patterned with this method, indicating that it is applicable to both hydrophobic and hydrophilic SAMs. This method provides a unique tool for fabricating cell microarrays and studying dynamical properties of living cells.