Synthesis of Curved Polycyclic Arenes Embedded with Oxepine and Thiepine Using Ring Expansion Strategy.

A tandem oxidative ring expansion of a six- to seven-membered ring was developed to construct a new class of negatively curved polycyclic arenes embedded with oxepine and thiepine, namely, dibenzo[b,f]phenanthro[9,10-d]oxepine (DBPO) and dibenzo[b,f]phenanthro[9,10-d]thiepine (DBPT), respectively. Mechanistic studies disclosed that an unexpected [4 + 2] cycloadduct formed between the alkene moiety of o-biphenyl-linked methylenexanthenes and o-chloranil serves as a radical cation or a dication equivalent that facilitates the FeCl3-mediated tandem ring expansion process.

Organocatalytic Atroposelective Construction of Axially Chiral Compounds Containing Benzimidazole and Quinoline Rings.

An organocatalytic atroposelective strategy for the construction of axially chiral compounds containing benzimidazole and quinoline rings is described. The enantioselective heteroannulation reaction of 2-alkynylbenzimidazoles with ortho-aminophenylketones proceeded smoothly in the presence of chiral phosphoric acid to provide axially chiral heterobiaryls with good yields and enantioselectivities. This is the first example of the combination of benzimidazole and quinoline rings at the 2- and 3-positions, respectively, into axially chiral heterobiaryls by this new strategy.

Construction of Alkylidene Fluorene Scaffolds Using Pd-Catalyzed Direct Arene/Alkene Coupling Strategy.

A versatile synthetic method for the construction of alkylidene fluorenes and their heteroarene derivatives has been developed successfully by means of a Pd(II)-catalyzed direct C-H/C-H coupling of o-alkenyl biaryls. Use of the Pd(OAc)2 catalyst under aerobic oxidation conditions gives rise to the corresponding alkylidene fluorenes having various functional groups and diversely fused polycyclic systems. The resulting products can serve as versatile synthetic building blocks for the construction of structurally diverse polycyclic arenes and heteroarenes.

Pd-Catalyzed Indolization/peri-C-H Annulation/N-Dealkylation Cascade to Cyclopenta-Fused Acenaphtho[1,2-b]indole Scaffold.

A novel Pd-catalyzed cascade reaction of N,N-dialkyl-substituted o-alkynylanilines involving an indolization/peri-C-H annulation/N-dealkylation sequence has been developed to construct a cyclopenta-fused acenaphtho[1,2-b]indole (ANI) scaffold. A variety of aromatic hydrocarbons having a peri-C-H bond at the alkynyl terminus, such as naphthalene, phenanthrene, pyrene, and fluoranthene, were employed, affording the corresponding π-extended ANI derivatives. The ANI molecules showed relatively narrow energy gaps by increasing HOMOs and lowering LUMOs, implying their potential applications as π-segments in low-band-gap materials.

Unsupported Nanoporous Platinum-Iron Bimetallic Catalyst for the Chemoselective Hydrogenation of Halonitrobenzenes to Haloanilines.

An unsupported nanoporous platinum-iron bimetallic catalyst (PtFeNPore) was prepared with an electrochemical dealloying technique. Its structure and composition were characterized through various measurement methods, such as X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). An intermetallic compound and iron oxide species were both found in the PtFeNPore catalyst. The nanoporous structure and Lewis acidity (caused by iron oxide species) of the PtFeNPore catalyst resulted in superior catalytic activity and high selectivity. The PtFeNPore-catalyzed hydrogenation of various halonitrobenzenes proceeded successfully under mild reaction conditions and produced good to excellent yields of the corresponding haloanilines with high selectivity. PtFeNPore can be recycled through magnetic separation easily and reused five times without significant deactivation.

Intermolecular Oxidative Friedel-Crafts Reaction Triggered Ring Expansion Affording 9,10-Diarylphenanthrenes.

A novel intermolecular tandem oxidative aromatic coupling between arylidene fluorenes and unfunctionalized aromatics mediated by a DDQ/TFA oxidation system has been developed for the construction of 9,10-diarylphenanthrenes (DAPs). The formation of a benzylic carbocation species possessing a quaternary sp3-carbon center on the fluorene moiety by an intermolecular oxidative Friedel-Crafts reaction of two different arenes successfully triggered the subsequent ring expansion to afford DAPs.

Amorphous/low-crystalline core/shell-type nanoparticles as highly efficient and self-stabilizing catalysts for alkaline hydrogen evolution.

Amorphous/low-crystalline core/shell-type nanoparticles (Pd-P/Pt-Ni NPs) were prepared via a facile seed-mediated method. After acid treatment, the NPs exhibited self-improved catalysis for hydrogen evolution during electrolysis in an alkaline medium.

Tandem Oxidative Ring Expansion for Synthesis of Dibenzocyclooctaphenanthrenes.

A novel tandem single-electron oxidative ring expansion reaction has been developed for the construction of the saddle-shaped polycyclic arenes fused with cyclooctatetraene, that is, dibenzo[3,4:7,8]cycloocta[1,2-l]phenanthrenes (dbCOTPs). The combination of Cu(OTf)2 catalyst with DDQ triggered the selective oxidation of o-biphenyl-tethered methylenecirculenes fused with a seven-membered ring, giving rise to the formation of the corresponding eight-membered ring fused dbCOTPs. The present tandem ring expansion of a seven- to an eight-membered ring takes place via the selective single-electron oxidation of the benzylidene moiety, intramolecular spirocyclization, and 1,2-aryl migration sequence.

Catalytic Performance of Nanoporous Metal Skeleton Catalysts for Molecular Transformations.

Nanoporous metal (MNPore) skeleton catalysts have attracted increasing attention in the field of green and sustainable heterogeneous catalysis owing to their unique three-dimensional nanopore structural features. In general, MNPores are fabricated through chemical or electrochemical corrosive dealloying of monolithic alloys. The dealloying process produces various MNPores with an open nanoporous network structure by formation of concave and convex hyperboloid-like ligaments. The large surface-to-volume ratio compared to bulk metals and high density of steps and kinks on ligaments of the unsupported MNPores make them promising heterogeneous catalyst candidates for highly active and selective molecular transformations. In this context, a variety of heterogeneous catalytic reactions using MNPores as nanocatalysts under gas- and liquid-phase conditions were developed over the last decade. In addition, the bulk metallic shape and mechanistic rigidity of the MNPore catalysts make the processes of catalyst recovery and reuse more facile and greener. This Minireview mainly focuses on the catalytic performance of nanoporous Au, Pd, Cu, and AuPd with respect to the achievements on catalytic applications in various molecular transformations.

Pd-Catalyzed cascade cyclization of o-alkynylanilines via C-H/C-N bond cleavage leading to dibenzo[a,c]carbazoles.

A new and efficient Pd-catalyzed cascade cyclization of biaryl-tethered o-alkynylanilines for the formation of dibenzo[a,c]carbazole derivatives has been reported. The use of the alkyl-substituted tertiary anilines together with the combination of the PdCl2 catalyst with the MnO2 oxidant and PivOH is vital for giving rise to 5-endo cyclization, C-N bond cleavage, and C-H bond activation in a cascade manner to produce the corresponding products with structural diversity.

Pd-Catalyzed Consecutive C-H-Arylation-Triggered Cyclotrimerization: Synthesis of Star-Shaped Benzotristhiazoles and Benzotrisoxazoles.

Star-shaped π-extended molecules comprising discotic aromatic cores and peripheral π-conjugated arms have attracted significant attention as diverse optoelectronic materials in terms of their large π-surface, tunable self-assembly, enhanced charge transport and fluorescence, and liquid crystallinity. Although many efforts have been made in the construction of various aromatic discotic cores, a new class of C3 -symmetric star-shaped discotic π-molecules consisting of electron-deficient benzotristhiazole and benzotrisoxazole cores, which are expected to exhibit distinct optoelectronic properties, remains unexplored owing to the unachievable synthetic approaches involved in their synthesis. Herein, we report a novel and highly efficient Pd-catalyzed cyclotrimerization of the functionalized thiazoles or oxazoles for the construction of a new class of discotic molecules of benzotristhiazole and benzotrisoxazole central cores with star-shaped π-conjugated arms. The combination of [Pd2 (dba)3 ]/XPhos (dba=dibenzylideneacetone) catalyst systems with the 4-bromo-substituted thiazole enables the formation of a sufficiently stable thiazole-Pd species that participates in the subsequent C-H arylations consecutively to form the corresponding cyclic trimer products. This new class of star-shaped discotic π-extended products showed tunable energy levels and high fluorescence quantum yields that make them promising candidates for optoelectronic applications.

Synthesis of extended polycyclic aromatic hydrocarbons by oxidative tandem spirocyclization and 1,2-aryl migration.

The extended polycyclic aromatic hydrocarbons (PAHs) have received significant interdisciplinary attention due to their semiconducting applications in diverse organic electronics as well as intriguing structural interests of well-defined graphene segments. Herein, a highly efficient oxidative spirocyclization and 1,2-aryl migration tandem synthetic method for the construction of extended polyaromatic hydrocarbons (PAHs) has been developed. The CuCl-catalyst/PhCO3tBu or DDQ oxidation system in the presence of trifluoroacetic acid enables the selective single-electron oxidation to take place preferentially at the more electron-rich alkene moiety of o-biphenylyl-substituted methylenefluorenes, giving rise to the subsequent tandem process. A variety of structurally diverse extended PAHs including functionalized dibenzo[g,p]chrysenes, benzo[f]naphtho[1,2-s]picene, hexabenzo[a,c,fg,j,l,op]tetracene, tetrabenzo[a,c,f,m]phenanthro[9,10-k]tetraphene, tetrabenzo[a,c,f,k]phenanthro[9,10-m]tetraphene, tetrabenzo[a,c,f,o]phenanthro[9,10-m]picene and S-type helicene have been readily synthesized.

Hierarchical nanoporosity enhanced reversible capacity of bicontinuous nanoporous metal based Li-O2 battery.

High-energy-density rechargeable Li-O2 batteries are one of few candidates that can meet the demands of electric drive vehicles and other high-energy applications because of the ultra-high theoretical specific energy. However, the practical realization of the high rechargeable capacity is usually limited by the conflicted requirements for porous cathodes in high porosity to store the solid reaction products Li2O2 and large accessible surface area for easy formation and decomposition of Li2O2. Here we designed a hierarchical and bicontinuous nanoporous structure by introducing secondary nanopores into the ligaments of coarsened nanoporous gold by two-step dealloying. The hierarchical and bicontinuous nanoporous gold cathode provides high porosity, large accessible surface area and sufficient mass transport path for high capacity and long cycling lifetime of Li-O2 batteries.

Unsupported Nanoporous Gold Catalyst for Chemoselective Hydrogenation Reactions under Low Pressure: Effect of Residual Silver on the Reaction.

For the first time, H-H dissociation on an unsupported nanoporous gold (AuNPore) surface is reported for chemoselective hydrogenation of C≡C, C═C, C═N, and C═O bonds under mild conditions (8 atm H2 pressure, 90 °C). Silver doping in AuNPore, which was inevitable for its preparation through a process of dealloying of Au-Ag alloy, exhibited a remarkable difference in catalytic activity between two catalysts, Au>99Ag1NPore and Au90Ag10NPore.The former was more active and the latter less active in H2 hydrogenation, while the reverse tendency was observed for O2 oxidation. This marked contrast between H2 reduction and O2 oxidation is discussed. Further, Au>99Ag1NPore showed a high chemoselectivity toward reduction of terminal alkynes in the presence of internal alkynes which was not achieved using supported gold nanoparticle catalysts and other previously known methods. Reductive amination, which has great significance in synthesis of amines due to its atom-economical nature, was also realized using Au>99Ag1NPore, and the Au>99Ag1NPore/H2 system showed a preference for the reduction of aldehydes in the presence of imines. In addition to this high chemoselectivity, easy recovery and high reusability of AuNPore make it a promising heterogeneous catalyst for hydrogenation reactions.

N-Methyl Transfer Induced Copper-Mediated Oxidative Diamination of Alkynes.

A novel intramolecular oxidative diamination of bis(2-aminophenyl)acetylene for the synthesis of the structurally intriguing π-conjugated polyheterocyclic scaffold, 5,10-dihydroindolo[3,2-b]indole (DHII), has been developed under Cu(hfacac)2/O2 oxidation systems. The structure design of bis(2-aminophenyl)acetylene bearing both N,N-dimethylamine and primary amine groups is crucial for constructing the corresponding DHII scaffold. Notably, an intermolecular N-methyl transfer from the nitrogen atom of N,N-dimethylamine to the primary amine takes place, which is a critical step for the successful implementation of the present annulation process.

2-Positional pyrene end-capped oligothiophenes for high performance organic field effect transistors.

Three new 2-positional pyrene end-capped oligothiophene co-oligomers, BPynT (n = 1, 2, 3), have been synthesized for application in organic field effect transistors (OFETs). BPy2T showed the highest hole mobility of 3.3 cm(2) V(-1) s(-1) in a single crystal OFET and a good photoluminescence efficiency of 32% in the crystalline state. A green light emission was observed for the OFET based on a BPy2T single crystal.

Biphenyl end-capped bithiazole co-oligomers for high performance organic thin film field effect transistors.

Two new regiospecific biphenyl end-capped bithiazole co-oligomers, BP2Tz(in) and BP2Tz(out), have been synthesized for application in thin film field effect transistors (TFTs). BP2Tz(in) with a 2,2'-bithiazole central unit exhibits a field effect hole mobility as high as 3.5 cm(2) V(-1) s(-1). Green light emission is demonstrated for highly balanced ambipoar TFTs based on both BP2Tz(in) and BP2Tz(out).

FeCl3-Mediated Oxidative Spirocyclization of Difluorenylidene Diarylethanes Leading to Dispiro[fluorene-9,5'-indeno[2,1-a]indene-10',9''-fluorene]s.

A novel FeCl3-mediated oxidative spirocyclization for construction of a new class of di-spirolinked π-conjugated molecules, dispiro[fluorene-9,5'-indeno[2,1-a]indene-10',9''-fluorene]s (DSFIIFs), has been reported. The combination of FeCl3 with FeO(OH) triggered an unprecedented double one-electron oxidation of difluorenylidene diarylethanes to afford the corresponding dispirocycles in high yields. The highest fluorescence quantum yield was up to 0.94 in solution. This protocol is also applicable to the synthesis of the non-spirolinked dihydroindenoindenes.

Manganese powder promoted highly efficient and selective synthesis of fullerene mono- and biscycloadducts at room temperature.

Discovery of an efficient, practical, and flexible synthetic method to produce various important electron acceptors for low-cost organic photovoltaics (OPVs) is highly desirable. Although the most commonly used acceptor materials, such as PC61BM, PC71BM, IC60BA, bisPC61BM have been proved to be promising for the OPVs, they are still very expensive mainly due to their low production yields and limited synthetic methods. Herein, we report an unprecedented and innovative synthetic method of a variety of fullerene mono- and biscycloadducts by using manganese powder as a promotor. The reaction of fullerenes with various dibromides proceeds efficiently and selectively under very mild conditions to give the corresponding cycloadducts in good to excellent yields. The combination of manganese power with DMSO additive is crucial for the successful implementation of the present cycloaddition. Notably, the standard OPV acceptors, such as PCBMs, have been obtained in extraordinarily high yields, which cannot be achieved under the previously reported methods.

Highly efficient heterogeneous aerobic cross-dehydrogenative coupling via C-H functionalization of tertiary amines using a nanoporous gold skeleton catalyst.

We report for the first time that zero-valent nanoporous gold (AuNPore) is a robust and green heterogeneous catalyst for α-C-H functionalization of various tertiary amines. AuNPore combines with molecular oxygen at 80 °C or tert-butyl hydrogen peroxide at room temperature and catalyses the heterogeneous cross-dehydrogenative coupling (CDC) reaction efficiently to afford the corresponding C-C and C-heteroatom coupling products in good to excellent yields with excellent reusability.