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A regioselective and Z-selective three-component silylalkoxylation of 1,3-diene using various alcohols, disilane, and a catalytic Pd/Cu/1,4-benzoquinone/O2 system is established in this Letter. The reaction generates tetra-substituted allyl silanes containing allyl ether moieties in up to 80% isolated yield and on a 1-10 mmol scale via oxidative coupling. A wide variety of substrates, including benzyl alcohol derivates, aliphatic alcohols, and bioactive compounds such as cholesterol, are suitable for use in the developed reaction system.

In this mini-review, we summarize the solution syntheses of N,N-dimethylformamide (DMF)-protected metal nanoparticles (NPs) and nanoclusters (NCs) and their use in catalytic reactions. Representative examples are given of external-stabilizer/protectant-free metal NP and NC syntheses by reduction with DMF. In this method, DMF has three roles, i.e., a solvent, reductant, and protectant. Recent applications of DMF-stabilized metal NPs are summarized. These applications have enabled a versatile organic transformation such as cross-coupling reactions, hydrosilylation, and methylation to be achieved. These reactions proceed under low catalyst loadings and ligandless conditions.

NbCl5-catalyzed [2 + 2 + 2] cycloaddition of nitriles with alkynes was used to synthesize pyrimidine derivatives. In this reaction, the use of individual Lewis acids, namely NbCl5 and FeCl3, is a key strategy for achieving the reaction using a catalytic amount of NbCl5. The roles of the two Lewis acids were investigated using FT-IR spectroscopy. The results showed that NbCl5 served as an efficient Lewis acid catalyst for nitrile activation, whereas FeCl3 showed stronger Lewis acidity toward pyrimidines, releasing NbCl5 into the catalytic cycle.

A NbCl5, Zn, and PCy3 catalytic system that generated low-valent Nb species is used for the synthesis of bicyclic cyclohexadienes from diynes and simple alkenes. A phosphine ligand is important for stabilizing low-valent Nb in the cycloaddition. The bicyclic cyclohexadiene skeleton is important in transition-metal-catalyzed intramolecular cycloadditions.

This paper summarizes recent advances in α-alkylation reactions based on hydrogen borrowing methodologies using alcohol as an alkylating agent. This review provides a summary of recent progress toward the α-alkylation of carbonyl substrates, as well as relatively unactivated substrates bearing fewer acidic α-hydrogens, such as acetonitriles, acetamides, esters, methylpyrimidines, and methylquinolines. A summary of recent improvements in α-methylation strategies based on hydrogen borrowing methodologies has also been provided. Particular emphasis has been placed on highly practical and green chemistry approaches involving modified catalytic systems, including metal-supported heterogeneous catalysts and nanoparticle-based catalysts, as well as reactions conducted in the absence of a transition-metal catalyst. A review of recent achievements in methylation strategies using methanol as a methyl source, and their application to the α-methylation of ketones using transition-metal catalyzed hydrogen borrowing me...

A catalytic system based on low-valent niobium has been developed, consisting of NbCl5, Zn, and an alkoxysilane. This combination has been shown to be an efficient catalyst for the synthesis of pyridine derivatives from the intermolecular cycloaddition of alkynes and nitriles via a niobacyclopentadiene intermediate.

Iridium-catalyzed alkylation of methylquinolines at the methyl substituent was achieved using alcohols as alkylating agents. The reaction proceeded through a transfer hydrogenation pathway from the alcohol to the Ir complex, affording an aldehyde and Ir-H species, followed by base-assisted aldol condensation and hydrogenation. This method provides an atom-economical and convenient route to alkylquinolines from easily accessible methylquinolines.

Intermolecular cycloadditions of alkynes (terminal alkynes and internal alkynes) with aryl nitriles were successfully achieved, using an NbCl5 complex, to give substituted pyrimidine derivatives in high yields with excellent chemo- and regioselectivity.

An active niobium catalyst was developed via a simple and nontoxic reduction method from NbCl(5)/hydrosilane and utilized for the selective [2 + 2 + 2] cycloaddition reaction of terminal alkynes and alkenes/α,ω-dienes, to give 1,3-cyclohexadiene derivatives in high yields with excellent chemo- and regioselectivity.

Intermolecular [2+2+2] cycloaddition of tert-butylacetylene with alpha,omega-dienes was successfully achieved by NbCl(3)(DME) catalyst to afford 5-omega-alkenyl-1,4-disubstituted-1,3-cyclohexadienes in excellent yields with high chemo- and regioselectivity.

Synthesis of omega-hydroxy carboxylic acids and alpha,omega-dimethyl diketones was successfully achieved by using alpha,omega-diols as alkylating agents under the influence of an iridium catalyst. For example, the alkylation of butyl cyanoacetate with 1,13-tridecanediol in the presence of [IrCl(cod)](2) or [IrCl(coe)(2)](2) gave rise to butyl 2-cyano-15-hydroxypentadecanoate in good yield which is easily converted to cyclopentadecanolide (CPDL). In addition, the alkylation of acetone with 1,10-decanediol in the presence of [IrCl(cod)](2) and KOH resulted in an important muscone precursor, 2,15-hexadecanedione (HDDO), in good yield.

The Beckmann rearrangement of ketoximes to lactams was successfully achieved by a very small amount of cyanuric chloride and phosphazene by carrying out the reaction in a mixed solvent of trifluoroacetic acid and toluene under mild conditions. For instance, the Beckmann rearrangement of cyclohexanone oxime was completely performed under the influence of 0.5 mol % of cyanuric chloride (CNC) or phosphazene (1,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-chloride: TAPC) in a 3:2 mixed solvent of trifluoroacetic acid and toluene at 70 °C for 4 h to give ϵ-caprolactam, which is an important monomer of 6-Nylon, in almost quantitative yield. The same strategy could be applied to laurolactam synthesis from cyclododecanone oxime.

A new synthetic method of substituted furoates from acrylates and aldehydes was developed by Pd(OAc)2 combined with molybdovanadophosphoric acid and Lewis acid under atmospheric dioxygen. The reaction was found to proceed through the palladium-catalyzed acetalization of acrylates with methanol followed by the reaction of the resulting acetals with aldehydes.

Kinetic resolution of 4-alkyl-2-aryl-5-oxo-4,5-dihydrooxazole-4-carboxylic acid esters (azlactones 1) were achieved by copper-DTBM-SEGPHOS catalyzed alcoholysis reaction with good selectivity (12 examples). Variation of ee of unreacted substrates 1 and products 2 with conversion was found to follow the theoretical line of zeroth-order kinetic resolution, for which the selectivity profiles and graphical analysis were presented for the first time. The efficiency of resolution in zeroth-order reaction is higher than first-order reaction. For example, the reaction with 1a afforded (S)-1a (99% ee) and (R)-2a (74% ee) at 57% conversion, where the k(rel) values were calculated to be 6.7 as zeroth-order kinetic resolution and 37 as first-order kinetic resolution.

Bowl-shaped phosphine (BSP) ligands markedly accelerated the rhodium-catalyzed hydrosilylation of ketones and ketimines as compared with the effect of conventional phosphine ligands such as PPh3 an...

[reaction: see text] Various kinds of transition metals catalyzed the hydrolysis of alkenyl esters and ethers under buffer-free, high concentration conditions compared to usual biocatalysts. Hydrolytic kinetic resolution of cis-2-tert-butylcyclohexyl vinyl ether was achieved by chiral (salen)Co complexes with good selectivity (k(rel) = 10.0).

The synthesis and complexation behavior of a novel bis-phosphine ligand based on a calix[4]arene scaffold, 5,17-bis(diphenylphosphino)-25,26,27,28-tetrabenzyloxycalix[4]arene (3), are reported. Reaction of 3 with PdCl2(cod) under dilute conditions results in formation of the trans-coordinated dinuclear complex [PdCl2·3]2 (4). The X-ray structure of 4 reveals that the two phosphinocalix[4]arene molecules are linked by the two PdCl2 fragments. On the other hand, reaction of 3 with PtCl2(cod) affords the cis-chelating mononuclear complex PtCl2·3 (5). The X-ray structure, low-temperature NMR measurements, and geometry optimization of 5 reveal that the structure in solution at −80 °C and in solid-state has a C1 symmetry where the P−Pt−P plane is inclined and the calix[4]arene moiety is twisted. It was also found that 3 reacts with [Pd(η3-C3H5)(cod)]BF4 to yield the corresponding cationic complex [Pd(η3-C3H5)·3]BF4 (6) quantitatively. Low-temperature NMR measurements suggest that 6 exists as a mixture of two st...

Preparation of novel mono- and bidentate phosphine ligands having dendrimer moiety is reported. Monodentate (1a−c) and bidentate ligands (5a,b) were synthesized from bis(4-hydroxyphenyl)phenylphosphine oxide (3) and 1,2-bis(dichlorophosphino)ethane, respectively, in high yields. The defect-free monodisperse nature of these compounds was confirmed by 31P NMR and elemental analysis as well as by ESI mass spectra. Complexation of these ligands with PtCl2(COD) followed by NaBH4 reduction in a THF/H2O mixture gave Pt(0) complexes 10a,b (having 1a,b as the ligands) and 13a,b (5a,b as the ligands). Monodentate ligands gave PtL3 complexes (10a,b) and bidentate ligands gave Pt(L−L)2 complexes (13a,b), respectively. Preliminary studies on oxidative addition of RI (R = CH3 or C6H5) to 10a,b showed that the metal center is easily accessible. Further, molecular modeling of 13b showed nanoscale flattened globular structure of the complex with an approximate diameter of 4.4 nm.

Intermolecular aerobic oxidative allylic amination of simple alkyl alkenes with simple amines such as diphenylamine was induced by a Pd(OCOCF(3))(2)/NPMoV catalytic system, leading to the corresponding (E)-allylamines in good yield and selectivity through the formation of (eta(3)-allyl)palladium(II) trifluoroacetate species as a possible key intermediate.

Treatment of bis(phenylethynyl)silane (PhC⋮C)2SiR2 (R = Me (2a), Et (2b) or Ph (2c)) with Cp2ZrEt2 (1) (Cp = cyclopentadienyl) and H2O/CuCl in this order afforded (1E,3E)-1,4-diphenyl-1,3-butadiene (3) in 56−88% yields after hydrolysis. On the other hand, hydrolysis of the reaction mixture of 2a−h with Cp2ZrEt2 gave silacyclobutene derivatives 4a−h in 61−87% yields. Zirconium-containing intermediate 7 was obtained as crystals suitable for X-ray analysis when t-BuC5H4 was used as the ligands of a zirconocene derivative. Structure of 7 showed that the intermediate contained the zirconacyclobutene−silacyclobutene fused ring system. Reaction of silacyclobutene 4a with CuCl selectively opened the silacyclobutene ring. The further treatment of the reaction mixture with PhI in the presence of a catalytic amount of Pd(PPh3)4 gave 1,3,4-triphenyl-1-silyl-1,3-butadiene compound 16. Zirconacyclopentadienes with an alkynylsilyl group at the α-position afforded zirconacyclohexadiene derivatives 19 in 82−98% yields. Wh...

In this paper we report the Cp‘2Ln/Me2SiCp‘‘2Ln-catalyzed (Cp‘ = η5-Me5C5; Cp‘‘ = η5-Me4C5) hydrogenation of acyclic imines to yield the corresponding amines. At 190 psi of H2, the observed turnover frequencies (h-1) (100:1 substrate:catalyst ratio, Cp‘2Ln, temperature (°C)) are (1) (N-benzylidene(methyl)amine, Ln = La, 50) 0.03; (Ln = Sm, 90) 1.0; (Ln = Sm + PhSiH3, 90) 2.2; (Ln = Lu, 90) 0.60; (2) (N-benzylideneaniline, Ln = Sm, 90) 0.10; (3) (N-benzylidene(trimethylsilyl)amine, Ln = Sm, 90) 0.40; (4) (N-(α-methylbenzylidene)(methyl)amine, Ln = Sm, 90) 0.20; (5) (N-(α-methylbenzylidene)(benzyl)amine, Ln = Sm, 90) 0.70. The stoichiometric reaction of N-benzylidene(methyl)amine with Cp‘2SmCH(SiMe3)2 or (Cp‘2SmH)2 yields an orthometalated Cp‘2Sm−substrate complex which undergoes either hydrogenolysis/hydrogenation or competing CN insertion of a second substrate molecule to yield a Cp‘2Sm-imine−amido complex with a seven-membered chelate ring. The stoichiometric reaction of 2-methyl-1-pyrroline with Cp‘2SmC...

A novel capsule-shaped Ir(I) and Rh(I) cationic complexes with a triphosphinocalix[6]arene as a ligand were synthesized. These complexes showed dynamic behavior with size-selective molecular encapsulation, which was confirmed by variable-temperature 31P{1H} NMR measurement in the presence of various molecules.

Palladium-catalyzed acylation of allylic trifluoroacetates (2) using acylstannanes (1) is reported. The reaction serves as a complementary method to the previously reported acylation with acylsilane (4). In particular, the reaction is profitable in the acylation of unsubstituted allyl trifluoroacetate (2a) and benzoylation of allylic trifluoroacetates to afford synthetically useful beta,gamma-unsaturated ketones (3) in good yields without undesirable isomerizations.

[reaction: see text]An equimolar mixture of propargylic carbonate (1) and trimethylsilyl cyanide (2) in THF under reflux affords cyanoallene (3) in the presence of a catalytic amount (5 mol %) of Pd(PPh3)4. In the reaction, the trimethylsilyl moiety of 2 effectively traps the leaving group of 1. The use of 2 in excess (6 equiv) provides dicyanated products (7 or 8) in high yields.

The synthesis and activity as precatalysts for stereoregular α-olefin polymerization of the chiral C1-symmetric zirconocene complexes (R)- and (S)-Me2Si(η5-C13H16)(η5-C5H3R*)ZrR2, where C13H16 = octahydrofluorenyl, R = NMe2, Cl, or Me, and R* = (1R,2S,5R)-trans-5-methyl-cis-2-(2-propyl)cyclohexyl ((−)-menthyl), are described.

Acetates were successfully alkylated with primary alcohols and alpha,omega-diols in the presence of tert-BuOK under the influence of [IrCl(cod)](2). For instance, the reaction of tert-butyl acetate with n-butanol in the presence of tert-BuOK as a base and [IrCl(cod)](2) as a catalyst in tert-BuOH at 100 degrees C produced tert-butyl hexanoate in good yield. When the alpha,omega-diol 1,9-nonanediol was employed, di-tert-butyl tridecanoate was obtained. These reactions are the first report of the alkylation of acetates using alcohols as alkylating agents. This method provides a very convenient direct route to carboxylates, which are very important raw materials in organic and industrial chemistry.

Palladium-diamine complexes catalyzed kinetic resolution of axially chiral 2,2'-dihydroxy-1,1'-biaryls by alcoholysis of vinyl ethers. The reaction proceeded with high selectivity for various kinds of biaryls. This process is applicable to not only binaphthols but also biphenols, which have been considered to be difficult for the enantioselective synthesis by known catalytic methods.

In homogeneous catalyst systems, there is the persistent problem that metal aggregation and precipitation cause catalyst decomposition and considerable loss of catalytic activity. Pd black formation is a typical example. Pd catalysts are known to easily aggregate and form Pd black, although they realize a wide variety of useful reactions in organic synthesis. In order to overcome this intrinsic problem of homogeneous Pd catalysis, we explored a new class of Pd catalyst by adopting aerobic oxidation of alcohols as a probe reaction. Herein we report a new catalyst system that suppresses the Pd black formation even under air and with a high substrate to catalyst molar ratio (S/C: more than 1000) in oxidation of alcohols. The novel pyridine derivatives having a 2,3,4,5-tetraphenylphenyl substituent and its higher dendritic unit at the 3-position of the pyridine ring were found to be excellent ligands with Pd(OAc)2 in the palladium-catalyzed air (balloon) oxidation of alcohols in toluene at 80 degrees C. Comparison with structurally related pyridine ligands revealed that introduction of the 2,3,4,5-tetraphenylphenyl substituent at the 3-position of pyridine ring effectively suppresses the Pd black formation, maintaining the catalytic activity for a long time to give aldehydes or ketones as products in high yields.