Synthesis, Photoluminescence, and Electroluminescence of Phosphorescent Dipyrido[3,2-a;2'3'-c]phenazine-Platinum(II) Complexes Bearing Hole-Transporting Acetylide Ligands.

In this study, novel phosphorescent dipyrido[3,2-a;2'3'-c]phenazine (dppz)-platinum(II)-phenylacetylide complexes were developed to fabricate non-doped organic light-emitting diodes (OLED) by solution-processing. To facilitate the charge carrier injection into the emitting layer (EML), 3,6-di-tert-butylcarbazole-functinalized phenylacetylides were employed. As for the dppz ligand, 9,9-dihexylfluoren-2-yl and 4-hexylthiophen-2-yl side-arms were introduced to the 2,7-positions, which led to reddish orange and red photoluminescence (PL), respectively, in solution and film states (PL wavelength: ca. 600 and ca. 625 nm, respectively). The carbazole-appended phenylacetylide ligands hardly affected the emission color, although unsubstituted phenylacetylides gave rise to aggregate- or excimer-based near-infrared PL with a low quantum yield. Two types of non-doped OLEDs were fabricated: single-layer and multilayer devices. In both devices, the organic layers were fabricated by spin-coating, and the EML consisted of a neat film of the corresponding platinum(II) complex. Therein, electroluminescence spectra corresponding to those of PL were observed. The single-layer devices exhibited low device efficiencies due to a deteriorated charge carrier balance. The multilayer devices possessed hole- and electron-transporting layers on the anode and cathode sides of the EML, respectively. Owing to an improved charge carrier balance, the multilayer devices exhibited higher device performance, affording considerably improved values of luminance and external quantum efficiency.

Innovative green oxidation of amines to imines under atmospheric oxygen.

In recent years, the development of environmentally benign molecular construction methods has been of great importance, and especially, resource recycling, high atomic efficiency, and low environmental impact are in high demand. From this point of view, attention has also been focused on the development of one-pot synthesis of pharmaceuticals and functional molecules. Imines are excellent synthetic intermediates of these useful molecules, and the environmentally friendly oxidative synthesis of imines from amines has been energetically developed using oxygen (or air), which is abundantly available on the Earth, as an oxidant. This review focuses on the latest innovative and green oxidation systems of amines to imines under atmospheric oxygen, and their application to one-pot/eco-friendly and sustainable synthesis of pharmaceuticals and functional molecules. In particular, catalytic systems that activate molecular oxygen are categorized and described in detail as transition metal catalytic systems, photoirradiated catalytic systems, and organocatalytic systems.

Potential of a Novel Chemical Compound Targeting Matrix Metalloprotease-13 for Early Osteoarthritis: An In Vitro Study.

Osteoarthritis is a progressive disease characterized by cartilage destruction in the joints. Matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) play key roles in osteoarthritis progression. In this study, we screened a chemical compound library to identify new drug candidates that target MMP and ADAMTS using a cytokine-stimulated OUMS-27 chondrosarcoma cells. By screening PCR-based mRNA expression, we selected 2-(8-methoxy-2-methyl-4-oxoquinolin-1(4H)-yl)-N-(3-methoxyphenyl) acetamide as a potential candidate. We found that 2-(8-methoxy-2-methyl-4-oxoquinolin-1(4H)-yl)-N-(3-methoxyphenyl) acetamide attenuated IL-1ß-induced MMP13 mRNA expression in a dose-dependent manner, without causing serious cytotoxicity. Signaling pathway analysis revealed that 2-(8-methoxy-2-methyl-4-oxoquinolin-1(4H)-yl)-N-(3-methoxyphenyl) acetamide attenuated ERK- and p-38-phosphorylation as well as JNK phosphorylation. We then examined the additive effect of 2-(8-methoxy-2-methyl-4-oxoquinolin-1(4H)-yl)-N-(3-methoxyphenyl) acetamide in combination with low-dose betamethasone on IL-1ß-stimulated cells. Combined treatment with 2-(8-methoxy-2-methyl-4-oxoquinolin-1(4H)-yl)-N-(3-methoxyphenyl) acetamide and betamethasone significantly attenuated MMP13 and ADAMTS9 mRNA expression. In conclusion, we identified a potential compound of interest that may help attenuate matrix-degrading enzymes in the early osteoarthritis-affected joints.

Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization.

The addition of interelement compounds with heteroatom-heteroatom single bonds to carbon-carbon unsaturated bonds under light irradiation is believed to be an atomically efficient method to procure materials with carbon-heteroatom bonds. In this study, we achieved the photoinduced bisphosphination of alkynes using the phosphorus interelement compound, tetraphenyldiphosphine monosulfide (1), to stereoselectively obtain the corresponding (E)-vic-1,2-bisphosphinoalkenes, which are important transition-metal ligands. The bisphosphination reaction was performed by mixing 1 and various alkynes and then exposing the mixture to light irradiation. Optimization of the conditions for the bisphosphination reaction resulted in a wide substrate range and excellent trans-selectivity. Moreover, the completely regioselective introduction of pentavalent and trivalent phosphorus groups to the terminal and internal positions of the alkynes, respectively, was achieved. We also found that the novel double-bond isomerization reaction of the synthesized bisphosphinated products occurred with a catalytic amount of a base under mild conditions. Our method for the photoinduced bisphosphination of carbon-carbon unsaturated compounds may have strong implications for both organic synthesis and organometallic and catalyst chemistry.

Transition-Metal-Free Synthesis of Unsymmetrical Diaryl Tellurides via SH2 Reaction of Aryl Radicals on Tellurium.

Although diaryl tellurides are parent organotellurium compounds, their synthesis methods, especially for unsymmetrical ones, are limited. This may be due to the instability of diaryl tellurides and their synthesis intermediates under reaction conditions. Radical reactions are known to exhibit excellent functional group selectivity; therefore, we focused on a bimolecular homolytic substitution (SH2) reaction between the aryl radical and diaryl ditelluride. Aryl radicals are generated from arylhydrazines in air and captured by diaryl ditellurides, resulting in a selective formation of unsymmetrical diaryl tellurides with high yields. The electronic effects of the substituents on both arylhydrazines and diaryl ditellurides on the SH2 reaction of tellurium are also discussed in detail.

One-Pot Construction of Diverse ß-Lactam Scaffolds via the Green Oxidation of Amines and Its Application to the Diastereoselective Synthesis of ß-Amino Acids.

In this study, a simple one-pot construction of ß-lactam scaffolds was successfully achieved via 4,6-dihydroxysalicylic acid-catalyzed organocatalytic oxidation of amines to imines using molecular oxygen. Although some imines are highly unstable and difficult to isolate by conventional methods, the organocatalytic oxidation of amines described herein, followed by their direct reaction with acyl chlorides in the presence of a base, afforded a series of new ß-lactam derivatives with excellent cis selectivity, which could not be synthesized and isolated by previously reported methods. Thus, this one-pot protocol will be one of the powerful methods applicable to the synthesis of various potential drug candidates and functional molecules. Furthermore, the subsequent hydrolysis of these ß-lactams successfully afforded the corresponding ß-amino acids as almost single diastereomers in up to 99% yields.

Clarification on the Reactivity of Diaryl Diselenides toward Hexacyclohexyldilead under Light.

In this study, the reactivity of organochalcogen compounds toward a representative alkyl-lead bond compound under light was investigated in detail. Under light irradiation, the Cy-Pb bond of Cy6Pb2 (Cy = cyclohexyl) undergoes homolytic cleavage to generate a cyclohexyl radical (Cy•). This radical can be successfully captured by diphenyl diselenide, which exhibits excellent carbon-radical-capturing ability. In the case of (PhS)2 and (PhTe)2, the yields of the corresponding cyclohexyl sulfides and tellurides were lower than that of (PhSe)2. This probably occurred due to the low carbon-radical-capturing ability of (PhS)2 and the high photosensitivity of the cyclohexyl-tellurium bond.

A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones.

A simple and efficient method for α-brominating lactones that affords α-bromolactones under mild conditions using tetraalkylammonium hydroxide (R4N+OH-) as a base was developed. Lactones are ring-opened with Br2 and a substoichiometric amount of PBr3, leading to good yields of the corresponding α-bromocarboxylic acids. Subsequent intramolecular cyclization over 1 h using a two-phase system (H2O/CHCl3) containing R4N+OH- afforded α-bromo lactones in good yields. This method can be applied at the 10 mmol scale using simple operations. α-Bromo-δ-valerolactone, which is extremely reactive and difficult to isolate, could be isolated and stored in a freezer for about one week using the developed method. Optimizing the solvent for environmentally friendly large-scale syntheses revealed that methyl ethyl ketone (MEK) was as effective. In addition, in situ-generated α-bromo-δ-valerolactone was directly converted into a sulfur-substituted functional lactone without difficulty by reacting it with a sulfur nucleophile in one pot without isolation. This new bromination system is expected to facilitate the industrial use of α-bromolactones as important intermediates.

Highly regio- and stereoselective phosphinylphosphination of terminal alkynes with tetraphenyldiphosphine monoxide under radical conditions.

The homolytic cleavage of the PV(O)-PIII bond in tetraphenyldiphosphine monoxide simultaneously provides both pentavalent and trivalent phosphorus-centered radicals with different reactivities. The method using V-40 as an initiator is successfully investigated for the regio- and stereoselective phosphinylphosphination of terminal alkynes giving the corresponding trans-isomers of 1-diphenylphosphinyl-2-diphenylthiophosphinyl-1-alkenes in good yields. The protocol can be applied to a wide variety of terminal alkynes including both alkyl- and arylalkynes.

Photoinduced Syntheses and Reactivities of Phosphorus-Containing Interelement Compounds.

The photoinduced reactions of tetraphenyldiphosphine disulfide with a range of organic dichalcogenides successfully afforded a series of phosphorus(V)-chalcogen interelement compounds via a radical process. The relative reactivities of the organic dichalcogenides (i.e., (PhS)2, (PhSe)2, and (PhTe)2) toward the PIII or PV groups in the diphosphine analogues under light were investigated in detail, and a convenient method was developed to form P-S or P-Se interelement compounds from tetraphenyldiphosphine disulfide and (PhS)2 or (PhSe)2 upon photoirradiation. Furthermore, the relative photochemical properties and reactivities of tetraphenyldiphophine (P-P interelement compound) and its analogues toward photoinduced radical addition reactions were also discussed. The formed P-E (E = S, Se) interelement compounds could be utilized for ionic reactions, and they could be transformed into various phosphine reagents via one-pot processes.

2,4,6-Trihydroxybenzoic Acid-Catalyzed Oxidative Ugi Reactions with Molecular Oxygen via Homo- and Cross-Coupling of Amines.

Metal-free, oxidative four-component Ugi reactions (U-4CRs) were conducted to synthesize dipeptides from two different amines, isocyanides, and carboxylic acids using 2,4,6-trihydroxybenzoic acid catalyst in O2 atmosphere. The organocatalytic U-4CRs proceed via oxidative cross-coupling of benzylamines with other aliphatic or aromatic amines to form imines, followed by condensation with isocyanides and carboxylic acids. The U-4CRs via cross-coupling of amines are rare, and the simple, metal-free procedures are advantageous for further applications in drug and heterocycle syntheses.

Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines.

Using tetraaryllead compounds (PbAr4) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)2 or Pd(PPh3)4 to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.

Palladium-Catalyzed Cyanothiolation of Internal Alkynes Using Organic Disulfides and tert-Butyl Isocyanide.

Despite the availability of selective synthetic approaches to multifunctionalized substituted olefins, the cyanothiolation of internal alkynes has been much less explored. Herein, we show that nonactivated internal alkynes can be successfully cyanothiolated with diaryl disulfides and tert-butyl isocyanide in the presence of a Pd catalyst (e.g., Pd(PPh3)4) with the release of isobutene and arenethiol to afford ß-thiolated alkenyl cyanides in yields of 34-89%.

Reductive Formation of a Vanadium(IV/V) Oxide Cluster Complex [V8O19(4,4'- tBubpy)3] Having a C3-Symmetric Propeller-Shaped Nonionic V8O19 Core.

A novel C3-symmetric propeller-shaped vanadium(IV/V) oxide cluster complex, [V8O19(4,4'- tBubpy)3] (V8'), has been synthesized from the reaction of the windmill-shaped vanadium(V) oxide cluster complex [V8O20(4,4'- tBubpy)4] (V8) with PPh3 under N2, whereas refluxing V8 in methanol or ethanol under N2 provides tetranuclear oxido(alkoxido)vanadium(IV/V) complexes [V4O6(OR)6(4,4'- tBubpy)2] [R = Me (V4'-Me) and Et (V4'-Et)]. The mixed-valent vanadium(IV/V) clusters V8' and V4' are converted back to V8 under O2. Interconversions of V4' and the oxido(alkoxido)vanadium(V) complexes [V4O8(OMe)4(4,4'- tBubpy)2] (V4) and [V7O17(OEt)(4,4'- tBubpy)3] (V7-Et) are also presented.

Metal-Free Blue Dye Synthesis: Oxidative Coupling of Benzylamines and N,N-Dimethylanilines to Yield 4,4'-Diaminotriarylmethanes in the Presence of Salicylic Acid as a Co-oxidant.

A convenient, novel, and metal-free method for the synthesis of 4,4'-diaminotriarylmethanes (DTMs) is described. This process is based on a one-pot condensation of benzylamines with N,N-dimethylaniline derivatives using 4,6-dihydroxysalicylic acid as a co-oxidant and N-iodosuccinimide as an oxidant. To the best of our knowledge, the present method provides the first reported synthesis of DTMs from benzylamines via oxidative C-N bond cleavage and subsequent double C-C bond formations. The obtained DTMs were then easily converted into a series of blue dyes upon treatment with tetrachloro-1,4-benzoquinone (chloranil). Although the production of triarylmethane dyes tends to require the use of toxic heavy metals, the present method is advantageous in that it is a metal-free and straightforward process.

A Benzoyl Peroxide/Diphenyl Diselenide Binary System for Functionalization of Alkynes Leading to Alkenyl and Alkynyl Selenides.

Binary systems consisting of benzoyl peroxide (BPO) and diorganyl diselenide are effective in the selective benzoyloxyselenation of internal alkynes to afford the corresponding ß-(benzoyloxy)alkenyl selenides in good yields. In contrast to internal alkynes, terminal alkynes undergo a novel C(sp)-H substitution with the phenylseleno group of the BPO/(PhSe)2 system, providing alkynyl selenides in good yields. Both selenation reactions might proceed via benzoyloxy selenide (PhC(O)O-SeAr) as a key intermediate for electrophilic addition to alkynes. The products alkenyl and alkynyl selenides are expected to be useful synthetic intermediates in organic synthesis.

Synthesis and Interconversion of V4, V7, and V8 Oxide Clusters: Unexpected Formation of Neutral Heptanuclear Oxido(alkoxido)vanadium(V) Clusters [V7O17(OR)(4,4'-(t)Bubpy)3] (R = Et, MeOC2H4).

The octanuclear oxidovanadium(V) complex [V8O20(4,4'-(t)Bubpy)4] (1; 4,4'-(t)Bubpy = 4,4'-di-tert-butyl-2,2'-bipyridine) was synthesized in multigram-scale quantities by the reaction of VOSO4 with 4,4'-(t)Bubpy in the presence of sodium benzoate under O2. The reaction of 1 with MeOH under air afforded the tetranuclear oxidovanadium(V) complex [V4O8(OMe)4(4,4'-(t)Bubpy)2] (2) selectively. In contrast, treatment of 1 with EtOH or MeOC2H4OH under air gave the heptanuclear oxidovanadium(V) complexes [V7O17(OR)(4,4'-(t)Bubpy)3] (R = Et (3a), MeOC2H4 (3b)) having an unprecedented neutral V7O17(OR) core. Although 3a and 3b are relatively stable in CH2Cl2, slow diffusion of Et2O into the solution of 3a in CH2Cl2 afforded 1 as yellow crystals. Complex 2 was also converted into 1 by recrystallization from CHCl3-CH2Cl2/Et2O. (1)H and (51)V NMR as well as electrospray ionization mass spectrometry studies of the behavior of 2 in CD2Cl2 suggested the formation of the methoxido analogue of 3 (3c, R = Me), which is considered to be an intermediate species in the conversion of 2 to 1. The present results provide a rare example of interconversion among neutral vanadium(V) oxide cluster complexes by changing the solvent systems.

A novel octanuclear vanadium(V) oxide cluster complex having an unprecedented neutral V8O20 core functionalized with 4,4'-di-tert-butyl-2,2'-bipyridine.

A novel octanuclear vanadium(V) oxide cluster complex, [V8O20(4,4'-(t)Bubpy)4] (1), was synthesized and characterized by single-crystal X-ray structure analysis to reveal that 1 has an unprecedented neutral V8O20 core. An unexpected interconversion between 1 and the methoxo(oxo)vanadium(V) cluster complex, [V4O8(OMe)4(4,4'-(t)Bubpy)2] (2), was observed upon changes in the solvent systems.

Crystal structure of (µ-hydrogen di-sulfato)-µ-oxido-bis-[(4,4'-di-tert-butyl-2,2'-bi-pyridine)-oxidovanadium(IV/V)] aceto-nitrile monosolvate.

The dinuclear oxidovanadium(IV/V) complex, [V2(HS2O8)O3(C18H24N2)2]·CH3CN or [V2O2(µ-O)(µ-H(SO4)2)(4,4'-tBubpy)2]·CH3CN (4,4'-tBubpy = 4,4'-di-tert-butyl-2,2'-bi-pyridine), has crystallographic C 2 symmetry and exhibits a distorted octa-hedral geometry around the vanadium center, where the two 4,4'-tBubpy ligands are nearly orthogonal to each other. The two vanadium ions are linked by an oxo anion and a unique protonated sulfate anion [H(SO4)2 3-]. In the crystal, inter-molecular C-H⋯π and π-π inter-actions between the 4,4'-tBubpy ligands are present, leading to a three-dimensional network.

Novel heterotetranuclear V2Mo2 or V2W2 complexes with 4,4'-di-tert-butyl-2,2'-bipyridine: syntheses, crystal structures, and catalytic activities.

Two novel heterotetranuclear complexes [V(2)O(2)(µ-MeO)(2)(µ-WO(4))(2)(4,4'-(t)Bubpy)(2)] (1) and [V(2)O(2)(µ-MeO)(2)(µ-MoO(4))(2)(4,4'-(t)Bubpy)(2)] (2) were synthesized, and the solid state structures of these complexes were revealed by single crystal X-ray crystallography. The heterotetranuclear complexes 1 and 2 are centrosymmetric building blocks, considered as consisting of two [VO(4,4'-(t)Bubpy)](3+) units bridged by µ-MO(4)(2-) (M = W or Mo) anions connected with methoxy groups. Furthermore, catalytic activities of 1 and 2 in the alcohol oxidation with hydrogen peroxide as terminal oxidants in water as solvent were investigated.