Regioselective Heck arylation of unsaturated alcohols by palladium catalysis in ionic liquid

In contrast to almost all of the known examples of Heck arylation of unsaturated alcohols, which yield predominately beta-arylated products, arylation under the Pd-DPPP catalysis in ionic liquid leads preferentially to aryl substitution at the alpha carbon, providing an easy pathway to this valuable class of olefins.     

Unusual case of catalysis by palladium clusters

An unusual for Pd catalysts dehydration of α-alkyl and α, α′-dialkylbenzyl alcohols PhCR′R″OH (R′ = H, Me, Et, Bu; R″ = H, Me) occurs in the presence of the palladium(I) cluster [Pd₄(CO)₄(OAc)₄] (1) in an inert atmosphere to form ethers PhCR′R″-O-CR′ R″ and water. The catalyst is an intermediate of cluster 1 reduction to Pd black, while neither the starting cluster 1, nor Pd black, which is the decomposition product, are active in the catalysis of this reaction.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 788–791, March, 2005.     

Regioselective synthesis of multifunctional hybrid polysiloxanes achieved by Pt-nanocluster catalysis

The first example of "Pt"-nanocluster-catalyzed regioselective generation of hybrid polymers via attachment of organic functionalities to evenly distributed Si-H bonds of poly(methylhydro)siloxane is described. In addition, participation of Pt-nanoclusters as an active catalyst was evidenced by various spectroscopic techniques during the catalytic transformations.     

Regioselective alkenylation of imidazoles by nickel/Lewis acid catalysis

Nickel/Lewis acid binary catalysis is found effective to direct regioselective alkenylation of imidazoles through C-H bond activation and stereoselective insertion of alkynes. Use of P(t-Bu)₃ as a ligand allows exclusive regioselective C(2)-alkenylation, while PCyp₃ is found effective for C(5)-alkenylation of C(2)-substituted imidazoles. The reaction demonstrates a broad scope of imidazoles and internal alkynes to give trisubstituted ethenes highly regio- and stereoselectively in modest to good yields.     

1,1-Regioselective alkenylboration of styrenes enabled by palladium catalysis

Despite the 1,2-difunctionalization reactions of styrenes have been well developed, the 1,1-regioselective addition reaction remains challenging. We disclose herein a palladium-catalyzed, highly 1,1-regioselective alkenylboration of styrenes by using alkenyl triflates and a diboron reagent as the coupling partners. A wide scope of styrenes derivatives and alkenyl triflates participate this reaction to provide the corresponding allyl boronates with high regioisomeric ratios. The success of this reaction is ascribed to the application of 1,10-phenanthroline-derivated ligand and the addition of ammonium chloride salt. Moreover, acrylate esters can also selectively afford the 1,1-alkenylboration products under the same reaction conditions.     

Regioselective oxidative ring-opening of cyclopropenyl carboxylates by visible light photoredox catalysis

Catalyzed by Ir(dFCF₃ppy)₂(dtbbpy)PF₆, several aroyl methylidenemalonates were synthesized in good to excellent yields via visible light photoredox-catalyzed the oxidative ring-opening of cyclopropenyl carboxylate derivatives. The possible mechanism of oxidative quenching cycle was proposed.     

Oxidative transformation of tert-cyclobutanols by palladium catalysis under oxygen atmosphere

Palladium(II)-catalyzed oxidative reaction of tert-cyclobutanols involving the cleavage of a C-C bond via beta-carbon elimination under atmospheric pressure of oxygen is described. An alkylpalladium intermediate produced by beta-carbon elimination from a Pd(II) alcoholate gives a variety of products, depending on the substituents on the cyclobutane ring, in which reactions such as dehydrogenative ring opening, ring expansion and ring contraction are involved. For some substrates, the addition of a catalytic amount of ethyl acrylate dramatically accelerates the reaction. In all cases, the dehydrogenative products are obtained and the Pd(II)-hydride species produced at the final stage can be converted again to active Pd(II) species by molecular oxygen.     

Direct acylation of aryl bromides with aldehydes by palladium catalysis

A new protocol for the direct acylation of aryl bromides with aldehydes is established. It appears to involve palladium-amine cooperative catalysis, affording synthetically important alkyl aryl ketones in moderate to excellent yields in a straightforward manner, and broadening the scope of metal-catalyzed coupling reactions.     

Ligand-free palladium catalysis of aryl coupling reactions facilitated by grinding

Ligand-free palladium-catalysed Suzuki coupling reactions and homo-couplings of boronic acids have been facilitated by grinding. The reactions are rapid (10-30 min) and can be performed without the need to exclude air and moisture.     

Asymmetric hydration of alkenes catalyzed by wool‐palladium complex

A wool‐palladium complex has been found to be able to catalyze the asymmetric hydration of 1‐octene to (S)‐(+)‐2‐octanol and 1‐decene to (R)‐(+)‐2‐decanol under 1 atm N₂ and at 70°C. The optical yields were greatly affected by Pd content in wool‐palladium complex, reaction time and so on, when the proper conditions were selected, (S)‐(+)‐2‐octanol and (R)‐(+)‐2‐decanol could be obtained in 83.2 and 75.6%e.e. optical yield respectively. This chiral natural biopolymer‐palladium complex catalyst was very easy to prepare and could be reused several times without appreciable change in catalytic activity. Copyright © 2004 John Wiley & Sons, Ltd.     

两价钯催化下烯醇钯中间体和亲电试剂的反应研究

根据在两价钯催化的亲核试剂－炔烃－α,β-不饱和羰基化合物的串联加成反应中所假设的烯醇钯中间体的机理,研究了炔酸烯丙酯化合物1和亲电试剂在两价钯催化下的反应。使用乙酰氮作为亲电试剂得到了β－乙酰氧基烯基－γ－丁丙酯3,这一结果为烯醇钯中间体的机理提供了一个实验证据。     

金掺杂对碳负载钯催化还原性能的促进作用

在许多催化应用中双金属的PdAu催化剂性能优于单金属催化剂.科研人员对具有可控纳米结构和高活性的PdAu催化剂进行了广泛的研究,但该催化剂的制备需要多步且通常步骤复杂.本文仅通过浸渍和焙烧制得了Au掺杂的负载型Pd催化剂,所得PdAu/C催化剂用于室温水相三氯乙烯加氢脱氯反应.当Pd和Au负载量分别为1.0 wt%和1.1 wt%时,在经过干燥、空气处理和H2还原的过程后,所制得的PdAu/C催化剂活性最高,初始转化频率(TOF)为34.0×10–2 molTCEmolPd–1 s–1,是单金属1.0 wt%Pd/C催化剂TOF (2.2×10–2 molTCEmolPd–1 s–1)的15倍以上. X射线吸收光谱结果表明,金的加入避免了400oC焙烧时Pd的氧化.本文还提出了可能的催化剂纳米结构演变路径,以解释所观察到的催化现象.     

Regioselective silylation of sugars through palladium nanoparticle-catalyzed silane alcoholysis

Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter. The silane alcoholysis reaction is an effective method for the regioselective silylation of methyl and phenyl glycosides and generates hydrogen gas as the only side product. For many of the sugar substrates investigated, the distribution of regioisomers obtained is complementary to that of the traditional R(3)SiCl/base (base = pyridine, imidazole) methodology and gives convenient access to the 3,6- rather than the 2,6-silylated pyranosides, obtained as the main product by the silyl chloride method. The method also allows a selective axial silylation of levoglucosan and 1,3,5-O-methylidene-myo-inositol. In an attempt to rationalize the observed regioselectivities, ab initio predictions (HF/3-21G) have been made on the relative energies of some of the silylated products. They suggest that the observed regioselectivities do not reflect a kinetic vs thermodynamic product distribution but are induced by the silylation agent employed. Models for the possible origin of the observed regioselectivity in both silylation methods (silane- and silyl chloride-based) are discussed.     

Regioselective 1,4-addition of nucleophiles to 1,3-diene monoepoxides catalyzed by palladium complex

1,3-Diene monoepoxides react with nucleophiles in the presence of palladium complex as a catalyst under neutral conditions to give 1,4-adducts selectively. The 1,4-adducts are allylic alcohols and there is a possibility of another nucleophilic attack. Ester of Monarch butterfly pheromone was prepared.     

Synthesis of 2-phenylindole N-derivatives under conditions of catalysis by palladium complexes

The synthesis of 2-phenylindole N-derivatives was accomplished. The synthesis included the catalytic coupling of o-iodoaniline with phenylacetylene leading to 2-aminotolan, the preparation of the derivative of the last at the nitrogen atom, and its catalytic cyclization to the corresponding indole.M. V. Lomonosov Moscow State University, Moscow 119899, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 194–198, February, 1999.     

Conjugate nucleophilic ring opening of activated vinylcyclopropanes facilitated by homogenous palladium catalysis

1,1-Diactivated-2-vinylcyclopropanes ($\text{1}$) add carbon nucleophiles ($\text{2}$) regiospecifically in a conjugate sense in the presence of a catalytic amount of a zerovalent palladium complex.     

Microwave-accelerated spiro-cyclizations of o-halobenzyl cyclohexenyl ethers by palladium(0) catalysis

A number of new spiro[cyclohexane-1,1'-isobenzofuran]-based compounds was synthesized by palladium(0)-catalyzed 5-exo cyclization of a series of cyclohexenyl o-halobenzyl ethers. Controlled microwave heating was found to promote both product yield and reaction rate without compromising the selectivity. Heck cyclization of aryl iodide 6, 2-(2-iodobenzyloxy)cyclohex-2-enyl acetate, proceeded selectively without involvement of the allylic acetate functionality.