Hydrogen Bond-Controlled Site-Selective C(sp)-H Alkylation of Sulfonanilides.

We successfully developed a decatungstate-catalyzed benzylic C(sp)-H alkylation of sulfonanilides by utilizing the hydrogen bond between the sulfonamide group of the substrates and decatungstate photocatalysts. Using this catalytic system, site-selective C(sp)-H alkylation was achieved at the benzylic position near the sulfonamide group.

Divergent Synthesis of Silacycles by Ligand-Controlled Rhodium-Catalyzed Annulation of (2-Hydrosilylaryl)acetylenes.

This study demonstrates the rhodium-catalyzed divergent synthesis of 5-, 5,6-, and 8-membered silacyclic compounds, such as benzosilole, silolosiline, and disilocine, from (2-hydrosilylaryl)acetylenes. To achieve high product selectivity, intra- and intermolecular reactions are controlled by tuning the mono- and bidentate phosphine ligands on the rhodium catalyst precursor. Deuterium labeling experiments and computational studies reveal that the annulation reaction proceeds via hydride transfer to the alkyne moiety.

Gold-Catalyzed Synthesis of 5H-Benzo[b]indeno[2,1-d]silines by Insertion of Vinyl Carbocations into the Si-H Bond.

We have developed a gold-catalyzed cascade reaction of aryldiynes bearing a hydrosilyl group to afford a variety of unexplored 5H-benzo[b]indeno[2,1-d]silines. The reaction system is applicable to the synthesis of bidirectionally π-extended silacycles from tetra(alkynyl)aryl compounds. Computational studies suggest that 5H-benzo[b]indeno[2,1-d]silines are formed via the insertion of a vinyl carbocation intermediate into the Si-H bond.

Bifunctional 1-Hydroxypyrene Photocatalyst for Hydrodesulfurization via Reductive C(Aryl)-S Bond Cleavage.

We developed the visible-light-induced hydrodesulfurization of alkyl aryl thioethers via the reductive cleavage of the C(aryl)-S bond using 1-hydroxypyrene as a Brønsted acid-reductant bifunctional photocatalyst. The hydrodesulfurization reaction proceeded under simple reaction conditions (1-hydroxypyrene and EtN in THF under purple LED illumination); this reaction did not require chemicals commonly used for hydrodesulfurization, such as hydrosilanes, transition metal catalysts, and/or stoichiometric amounts of metal reagents. Detailed mechanistic studies based on control experiments, spectroscopic measurements, and computational studies revealed that the cleavage of the C(aryl)-S bond and the formation of the C(aryl)-H bond proceeded via the formation of the ion pair between the radical anion of alkyl aryl thioether and EtNH, resulting in the generation of a sulfur radical.

Photoinduced Divergent Deaminative Borylation and Hydrodeamination of Primary Aromatic Amines.

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.

Synthesis of fluorenes and their related compounds from biaryls and Meldrum's acid derivatives.

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 -terphenyl as substrates, respectively.

Facile synthesis of tribenzosilepins from terphenyls and dihydrosilanes by electrophilic double silylation.

Tribenzosilepins were synthesized from terphenyls and dihydrosilanes via a facile approach using a double sila-Friedel-Crafts reaction. Several silepin derivatives were obtained in moderate to high yield. The reaction system was found to be suitable for synthesizing a bidirectional silepin.

Photoinduced Deaminative Borylation of Unreactive Aromatic Amines Enhanced by CO.

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 (Bpin) 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 CO atmosphere which probably reduced the inhibitory effect of aminoborane.

Homogeneous and Heterogeneous Gold Catalysis for Materials Science.

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.

Gold-Catalyzed Annulation of 1,8-Dialkynylnaphthalenes: Synthesis and Photoelectric Properties of Indenophenalene-Based Derivatives.

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.

Synthesis, structures and photophysical properties of hexacoordinated organosilicon compounds with 2-(2-pyridyl)phenyl groups.

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.

Synthesis of six-membered silacycles by borane-catalyzed double sila-Friedel-Crafts reaction.

We have developed a catalytic synthetic method to prepare phenoxasilins. A borane-catalyzed double sila-Friedel-Crafts reaction between amino group-containing diaryl ethers and dihydrosilanes can be used to prepare a variety of phenoxasilin derivatives in good to excellent yields. The optimized reaction conditions were also applicable for diaryl thioethers to afford their corresponding six-membered silacyclic products.

Lewis acid-catalyzed synthesis of silafluorene derivatives from biphenyls and dihydrosilanes via a double sila-Friedel-Crafts reaction.

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.

Gold-Catalyzed Regiospecific Annulation of Unsymmetrically Substituted 1,5-Diynes for the Precise Synthesis of Bispentalenes.

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.

Chemodivergent reaction of azomethine imines and 2H-azirines for the synthesis of nitrogen-containing scaffolds.

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.

Dual Gold/Silver Catalysis Involving Alkynylgold(III) Intermediates Formed by Oxidative Addition and Silver-Catalyzed C-H Activation for the Direct Alkynylation of Cyclopropenes.

While gold-mediated synergistic catalytic processes involving transmetalations with other metals are well understood, Au /Au 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 Au complex formed by oxidative addition and one involving a silver-mediated C-H activation.

New transmetalation reagents for the gold-catalyzed visible light-enabled C(sp or sp)-C(sp) cross-coupling with aryldiazonium salts in the absence of a photosensitizer.

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.

Gold-Catalyzed Facile Synthesis and Crystal Structures of Benzene-/Naphthalene-Based Bispentalenes as Organic Semiconductors.

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 Combination of Benzaldehyde and Nickel-Catalyzed Photoredox C(sp )-H Alkylation/Arylation.

Herein we report a highly selective photoredox C(sp )-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(sp )-H alkylation/arylation of ethers. A selective late-stage modification of (-)-ambroxide has also been conducted to demonstrate the applicability of the method.

Light-Induced Gold-Catalyzed Hiyama Arylation: A Coupling Access to Biarylboronates.

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 sp - and sp -hybridized biarylboronates were obtained.

N-Heterocycle-Fused Pentalenes by a Gold-Catalyzed Annulation of Diethynyl-Quinoxalines and -Phenazines.

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.

Gold-Catalyzed Regiospecific C-H Annulation of o-Ethynylbiaryls with Anthranils: π-Extension by Ring-Expansion En Route to N-Doped PAHs.

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.

Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2-Cyclopentenones.

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.

Photopatterning Proteins and Cells in Aqueous Environment Using TiO2 Photocatalysis.

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.

SilverCatalyzed Cascade Carboxylation and Cyclization of Trimethyl(2-methylenebut-3-yn-1-yl)silane Derivatives.

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.