Creation of a Chiral All-Carbon Quaternary Center Induced by CF3 and CH3 Substituents via Cu-Catalyzed Asymmetric Conjugate Addition.

Cu-catalyzed asymmetric construction of a chiral quaternary center bearing CH3 and CF3 groups was achieved with high to excellent enantioselectivity using our originally developed ligands. The asymmetric conjugate addition of Me3Al to ß-CF3-substituted enones and unsaturated ketoesters proceeded efficiently. The use of unsaturated ketoesters gives optically active furanones in high yields with high enantioselectivities. The perfluoroalkyl-substituted enone does not seem to be favorable in the present reaction.

Cyclopropenes for the Stepwise Synthesis of 1,2,4,5-Tetraarylbenzenes via 1,4-Cyclohexadienes.

This paper describes a synthetic approach to the synthesis of 1,2,4,5-tetraarylbenzene derivatives from cyclopropenes. The Lewis acid-mediated dimerization of cyclopropenes gives tricyclo[3.1.0.02,4]hexane derivatives. The subsequent thermal ring-opening reaction under solvent-free conditions gives 1,4-cyclohexadienes bearing quaternary carbons. The novel Br2-mediated oxidative rearrangement of 1,4-cyclohexadienes takes place to give 1,2,4,5-tetraarylbenzene derivatives in high to excellent yields.

Regio- and Stereoselective Synthesis of Multi-Alkylated Allylic Boronates through Three-Component Coupling Reactions between Allenes, Alkyl Halides, and a Diboron Reagent.

Multisubstituted allylic boronates are attractive and valuable precursors for the rapid and stereoselective construction of densely substituted carbon skeletons. Herein, we report the first synthetic approach for differentially 2,3,3-trialkyl-substituted allylic boronates that contain a stereodefined tetrasubstituted alkene structure. Copper(I)-catalyzed regio- and stereoselective three-component coupling reactions between gem-dialkylallenes, alkyl halides, and a diboron reagent afforded sterically congested allylic boronates. The allylboration of aldehydes diastereoselectively furnished the corresponding homoallylic alcohols that bear a quaternary carbon. A computational study revealed that the selectivity-determining mechanism was correlated to the coordination of a boryl copper(I) species to the allene substrate as well as the borylcupration step.

Copper(I)-Catalyzed Enantioconvergent Borylation of Racemic Benzyl Chlorides Enabled by Quadrant-by-Quadrant Structure Modification of Chiral Bisphosphine Ligands.

The first copper(I)-catalyzed enantioselective borylation of racemic benzyl chlorides has been realized by a quadrant-by-quadrant structure modulation of QuinoxP*-type bisphosphine ligands. This reaction converts racemic mixtures of secondary benzyl chlorides into the corresponding chiral benzylboronates with high enantioselectivity (up to 92 % ee). The results of mechanistic studies suggest the formation of a benzylic radical intermediate. The results of DFT calculations indicate that the optimal bisphosphine-copper(I) catalyst engages in noncovalent interactions that efficiently recognize the radical intermediate, and leads to high levels of enantioselectivity.

Semireduction of Alkynes Using Formic Acid with Reusable Pd-Catalysts.

The treatment of PdCl2 with K2CO3 and HCO2H in dioxane gives black precipitates, which are an effective catalyst for the semireduction of alkynes to alkenes using formic acid as a reductant. Even 0.05 mol % Pd promoted the reduction reaction of tolane in high yield with high selectivity.

Post-Treatment-Free Solution-Processed Reduced Phosphomolybdic Acid Containing Molybdenum Oxide Units for Efficient Hole-Injection Layers in Organic Light-Emitting Devices.

We report the development of solution-processed reduced phosphomolybdic acid (rPMA) containing molybdenum oxide units for post-treatment-free hole-injection layers (HILs) in organic light-emitting devices (OLEDs). The physical and chemical properties of rPMA, including its structure, solubility in several solvents, film surface roughness, work function, and valence states, were investigated. The formation of gap states just below the Fermi level of rPMA was observed. Without any post-treatment after the formation of rPMA films, OLEDs employing rPMA as an HIL exhibited a very low driving voltage and a high luminous efficiency. The low driving voltage was attributed to the energy level alignment between the gap states formed by reduction and the HOMO level of the hole-transport layer material N,N'-bis(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine.

Polyoxometalate-Assisted, One-Pot Synthesis of a Pentakis[(triphenylphosphane)gold]ammonium(2+) Cation Containing Regular Trigonal-Bipyramidal Geometries of Five Bonds to Nitrogen.

Novel intercluster compounds consisting of pentakis[(triphenylphosphane)gold]ammonium(2+) cation (1) and Keggin polyoxometalate (POM) anions, i.e., {[Au(PPh3)]5(µ5-N)}3[α-PM12O40]2 (1-PW for M = W; 1-PMo for M = Mo), were synthesized in 30-36% yield by one-pot reaction of the protonic acid form of the Keggin POMs, H3[α-PM12O40]·nH2O (n = 13 for M = W; n = 15 for M = Mo) with monomeric (triphenylphosphane)gold(I) carboxylate [Au(RS-pyrrld)(PPh3)] [RS-Hpyrrld = (RS)-2-pyrrolidone-5-carboxylic acid] in the presence of aqueous NH3 at a molar ratio of 2:15:x (x = 3 for 1-PW; x = 7.5 for 1-PMo). These compounds resulted from the nitrogen-centered phosphanegold(I) clusterization of in situ generated monomeric phosphanegold(I) units, [Au(PPh3)]+ or [Au(L)(PPh3)]+ (L = NH3 or solvent), during the carboxylate elimination of [Au(RS-pyrrld)(PPh3)] in the presence of the Keggin POMs and aqueous NH3. The products 1-PW and 1-PMo were characterized by elemental analysis, Fourier transform infrared, thermogravimetric and differential thermal analyses (TGA/DTA), X-ray crystallography, and solid-state cross-polarization magic-angle-spinning (CPMAS) (31P and 15N) and solution (31P{1H} and 1H) NMR spectroscopy. The lattice contained three independent {[Au(PPh3)]5(µ5-N)}2+ cations, of which two took regular trigonal-bipyramidal (TBP) geometries and the third took a distorted, square-pyramidal (SP) geometry. These geometries are in contrast to those reported by Schmidbaur's group for {[Au(PPh3)]5(µ5-N)}2+ cations as BF4 salts. Density functional theory and ONIOM calculations for {[(L3P)Au]nN}(n-3)+ (L = H or Ph; n = 4-6) showed that the pentacoordinate cluster is energetically most stable and its TBP structure is only 1.6 kcal mol-1 more stable than its SP structure, in accordance with the experimental facts.

Silver-Catalyzed Allylation of Ketones and Intramolecular Cyclization through Carbene Intermediates from Cyclopropenes Under Ambient Conditions.

Tandem C-C bond formation was achieved through silver-catalyzed ring-opening of cyclopropenes via carbene intermediates. The reaction of cyclopropenes in the presence of a silver catalyst gave indene derivatives under ambient conditions. In contrast, the insertion of organozinc reagents to silver carbene or allylic cation intermediates afforded allylmetal intermediates for the tandem allylation of carbonyl compounds.

(Z)-Selective Enol Triflation of α-Alkoxyacetoaldehydes: Application to Synthesis of (Z)-Allylic Alcohols via Cross-Coupling Reaction and [1,2]-Wittig Rearrangement.

The stereoselective transformation of α-alkoxyacetoaldehydes to the corresponding (Z)-vinyl triflates was achieved by treatment with phenyl triflimide and DBU. The stereochemistry was explained by the "syn-effect," which was attributed primarily to an σ → π* interaction. The ß-alkoxy vinyl triflates obtained were applied to the stereoselective synthesis of structurally diverse (Z)-allylic alcohols via transition metal-catalyzed cross-coupling reaction and [1,2]-Wittig rearrangement.

Highly chemo-, enantio-, and regioselective synthesis of α,α-disubstituted furanones by Cu-catalyzed conjugate addition.

A highly chemo-, enantio-, and regioselective synthesis of furanones bearing an α,α-disubstituted quaternary stereogenic center is reported. The Cu-catalyzed enantioselective conjugate addition of organoaluminum reagents to unsaturated ketoesters at room temperature and subsequent lactonization took place. Synthetic transformations of furanones represent facile approaches to various cyclic or acyclic compounds bearing a quaternary stereogenic center.

Catalytic tandem C-C bond formation/cleavage of cyclopropene for allylzincation of aldehydes or aldimine using organozinc reagents.

The tandem allylation of aldehydes or an aldimine with allylzinc intermediates derived from organozinc reagents and cyclopropenes is described. The present three-component reaction involves carbozincation of cyclopropene and sequential cleavage of a cyclopropylzinc intermediate in situ without a transition-metal catalyst. The allylzinc intermediates generated in situ, which is an α,ß-unsaturated acylanion equivalent, gave the corresponding homoallylic alcohols or amine in good yields.

Stereoselective synthesis of (2Z,4E)-2,4-pentadien-1-ols via sequential 1,4-elimination reaction and [1,2]-Wittig rearrangement starting from (E)-4-alkoxy-2-butenyl benzoates.

The sequential 1,4-elimination reaction of (E)-4-alkoxy-2-butenyl benzoates and [1,2]-Wittig rearrangement gave (2Z,4E)-2,4-pentadien-1-ols stereoselectively. Z-Selective formation of intermediary vinyl ethers, whose stereochemistry was well elucidated by the "syn-effect", was achieved by treatment of the 2-butenyl benzoates with KOH in the presence of Pd catalyst. The subsequent [1,2]-Wittg rearrangement by use of n-BuLi proceeded with retention of the stereochemistry of the intermediary vinyl ethers.

Magnesium-tartramide complex mediated asymmetric Strecker-type reaction of nitrones using cyanohydrin.

An asymmetric Strecker-type reaction of nitrones using acetone cyanohydrin as a source of HCN has been realized. A magnesium-tartramide complex, generated from (R,R)-2,3-dihydroxy-1,4-di(pyrrolidin-1-yl)-butane-1,4-dione and MeMgBr, promoted transcyanation from the bromomagnesium salt of the cyanohydrin, in the presence of a catalytic amount of DBU, to afford the corresponding optically active (S)-α-amino nitrile derivatives. The reaction was applicable to various nitrones giving high-to-excellent enantioselectivities.

Effect of multinuclear copper/aluminum complexes in highly asymmetric conjugate addition of trimethylaluminum to acyclic enones.

Al and friends: asymmetric conjugate addition of Me(3)Al to ß,ß-disubstituted α,ß-unsaturated ketones in the presence copper and L1 leads to a highly efficient construction of an all-carbon-substituted chiral quaternary center. This result is the first example of an asymmetric conjugate addition of Me(3)Al to acyclic enones to give a chiral quaternary carbon center with excellent yield and enantioselectivity under mild reaction conditions.

One-pot synthesis of symmetrical and unsymmetrical diarylmethanes via diborylmethane.

A one-pot synthesis of diarylmethanes from air-stable diborylmethane via the Suzuki-Miyaura cross-coupling reaction is described. The present approach realizes the synthesis of various symmetrical and unsymmetrical diarylmethanes in good to excellent yields.

Cross coupling between sp3-carbon and sp3-carbon using a diborylmethane derivative at room temperature.

A novel example of the Suzuki-Miyaura cross-coupling reaction between sp(3)-carbon and sp(3)-carbon is described. The reaction of a diborylmethane derivative with allyl halides or benzyl halides proceeded efficiently in the presence of appropriate Pd-catalysts at room temperature. The present approaches provide functionalized homoallylboronates and alkylboronates with excellent regio- and chemoselectivities.

Multinuclear Cu-catalysts based on SPINOL-PHOS in asymmetric conjugate addition of organozinc reagents.

Multinuclear Cu/Zn complex-catalyzed efficient asymmetric conjugate addition of organozinc reagents to acyclic and cyclic enones has been developed in the presence of a wide variety of regioisomeric chiral diols bearing phosphorus moieties as ligands. The regioisomeric SPINOL-PHOS ligands based on a SPINOL architecture showed an unexpected inversion of stereoselectivity.

Ru-catalyzed ß-selective and enantioselective addition of amines to styrenes initiated by direct arene-exchange.

A catalytic ß-selective addition of amines to styrenes proceeded in the presence of cationic Ru complexes combined with diphosphine ligands. In the reaction of α-methylstyrene, an enantioselective addition was achieved by using xylylBINAP.

Ir(I)-catalyzed intermolecular regio- and enantioselective hydroamination of alkenes with heteroaromatic amines.

A cationic Ir(I)-C(3)-TUNEPHOS complex catalyzed an intermolecular hydroamination of styrene derivatives with various heteroaromatic amines. The reaction gave Markovnikov products with perfect regioselectivity and good enantioselectivity under solvent-free conditions.

Highly enantioselective synthesis of silahelicenes using Ir-catalyzed [2+2+2] cycloaddition.

Silahelicenes, which contain two silole moieties in a helically chiral structure, were synthesized by a chiral Ir-catalyzed intermolecular [2+2+2] cycloaddition of tetraynes with diynes along with a Ni-mediated intramolecular [2+2+2] cycloaddition. The photophysical properties of the obtained highly enantiomerically enriched silahelicenes (up to 93% ee) were also measured.