Oxidative cross-coupling of allyl(trimethyl)silanes with aryl boronic acids by palladium catalysis

The first oxidative cross-coupling of allylsilanes with aryl boronic acids has been developed by palladium catalysis. The reaction between β-substituted allyl(trimethyl)silanes and a wide range of aryl boronic acids afforded allylarenes in moderate to good yields and excellent selectivity. On the basis of experimental results and literature reports, it was suggested that the reaction might start from transmetalation of aryl boronic acid with AgOAc followed by transmetalation with Pd(II) to give an arylpalladium acetate complex as a key intermediate. This intermediate underwent either electrophilic addition/desilylation or transmetalation with allylsilane and subsequent reductive elimination to give the final product.     

Control of the regioselectivity in catalytic transformations involving amphiphilic bis-allylpalladium intermediates: mechanism and synthetic applications

Various dialkyl-substituted allyl chloride derivatives (2d-i) undergo regioselective palladium-catalyzed coupling reactions with allylstannanes (1a,b) and benzylidenemalonitrile (4), providing functionalized 1,7-octadienes in good yield. The catalytic reaction proceeds through an unsymmetrical amphiphilic bis-allylpalladium intermediate. An introductory electrophilic attack on the terminal position of the unsubstituted allyl moiety is followed by a nucleophilic attack on the alkyl-substituted allyl ligand. A theoretical analysis was performed by applying density functional theory at the B3PW91/DZ+P level to study the substituent effects on the electrophilic attack. According to the theoretical results, the high regioselectivity can be ascribed to the electronic effects of the alkyl substituents: The terminal alkyl groups destabilize the eta(1),eta(3)-bis-allylpalladium intermediate of the reaction; in addition, the alkyl substitution increases the activation barrier for the electrophilic attack.     

Regio- and stereoselective palladium-pincer complex catalyzed allylation of sulfonylimines with trifluoro(allyl)borates and allylstannanes: a combined experimental and theoretical study

Regio- and stereoselective palladium-pincer complex catalyzed allylation of sulfonylimines has been performed by using substituted trifluoro(allyl)borates and trimethylallylstannanes. The reactions provide the corresponding branched allylic products with excellent regioselectivity. The stereoselectivity of these processes is very high when trifluoro(cinnamyl)borate and trimethyl cinnamyl stannane are employed as allylic precursors; however, the reaction with trifluoro(crotyl)borate results in poor stereoselectivity. The major diastereomer formed in these reactions was the syn isomer, while the (previously reported) reactions with aldehyde electrophiles afforded the anti products, indicating that the mechanism of the stereoselection is dependent on the applied electrophile. Therefore, we have studied the mechanistic aspects of the allylation reactions by experimental studies and DFT modeling. The experimental mechanistic studies have clearly shown that potassium trifluoro(allyl)borate undergoes transmetallation with palladium-pincer complex 1 a affording an eta(1)-allylpalladium-pincer complex (1 e). The mechanism of the transfer of the allyl moiety from palladium to the sulfonylimine substrate was studied by DFT calculations at the B3PW91/LANL2DZ+P level of theory. These calculations have shown that the electrophilic substitution of sulfonylimines proceeds in a one-step process with a relatively low activation energy. The topology of the potential energy surface in the vicinity of the transition-state structure proved to be rather complicated as nine different geometries with similar energies were located as first order saddle points. Our studies have also shown that the high stereoselectivity with cinnamyl metal reagents stems from steric interactions in the TS structure of the allylation reaction. In addition, these studies have revealed that the mechanism of the stereoselection in the allylation of aldehydes and sulfonylimines is fundamentally different.     

Copper-catalyzed allylation of carbonyl derivatives using allyl(2-pyridyl)silanes

[reaction: see text] We have developed an efficient copper-catalyzed allylation of carbonyl derivatives using allyl(2-pyridyl)silanes, in which the strong directing effect of the 2-pyridyl group was observed. A useful synthesis and allylation of substituted allyl(2-pyridyl)silanes is also described.     

An efficient synthesis of vinylsilanes from acylsilanes and alkyl 1-phenyl-1H-tetrazol-5-yl sulfones. Brook vs Smiles rearrangement

[reaction: see text] Vinylsilanes are formed in high yields in the reaction of representative acyl(trimethyl)silanes with anions generated from Kocienski's sulfones.     

Reaction of 5-Allyl-5-Isobutylbarbituric Acid with Electrophilic Reagents

The reaction of 5-allyl-5-isobutylbarbituric acid with several electrophilic reagents gives products resulting from the addition of the electrophile to the double bond of the allyl group and/or bicyclic products.     

Origin of the regio- and stereoselectivity in palladium-catalyzed electrophilic substitution via bis(allyl)palladium complexes

Palladium-catalyzed allylic substitution of aryl allyl chlorides with aromatic and heteroaromatic aldehydes was performed in the presence of hexamethylditin. This procedure involves palladium-catalyzed formation of transient allylstannanes followed by generation of a bis(allyl)palladium intermediate, which subsequently reacts with the aldehyde electrophile. The catalytic substitution reaction proceeds with high regio- and stereoselectivity. The stereoselectivity is affected by the steric and electronic properties of the allylic substituents. Various functionalities including NO(2), COCH(3), Br, and F groups are tolerated under the applied catalytic conditions. Density functional calculations at the B3PW91/DZ+P level of theory were applied to study the steric and electronic effects controlling the regio- and stereoselectivity of the electrophilic addition. The development of the selectivity was studied by modeling the various bis(allyl)palladium species occurring in the palladium-catalyzed substitution of cinnamyl chloride with benzaldehyde. It was found that the electrophilic attack proceeds via a six-membered cyclic transition state, which has a pronounced chair conformation. The regioselectivity of the reaction is controlled by the location of the phenyl group on the eta(1)-allyl moiety of the complex. The stereoselectivity of the addition process is determined by the relative configuration of the phenyl substituents across the developing carbon-carbon bond. The lowest energy path corresponds to the formation of the branched allylic isomer with the phenyl groups in anti configuration, which is in excellent agreement with the experimental findings.     

Stereocontrolled Synthesis of Vinyl Boronates and Vinyl Silanes via Atom‐Economical Ruthenium‐Catalyzed Alkene–Alkyne Coupling

The synthesis of vinyl boronates and vinyl silanes was achieved by employing a Ru‐catalyzed alkene–alkyne coupling reaction of allyl boronates or allyl silanes with various alkynes. The double bond geometry in the generated vinyl boronates can be remotely controlled by the juxtaposing boron‐ and silicon groups on the alkyne substrate. The synthetic utility of the coupling products has been demonstrated in a variety of synthetic transformations, including iterative cross‐coupling reactions, and a Chan‐Lam‐type allyloxylation followed by a Claisen rearrangement. A sequential one‐pot alkene‐alkyne‐coupling/allylation‐sequence with an aldehyde to deliver a highly complex α‐silyl‐β‐hydroxy olefin with a handle for further functionalization was also realized.     

Silicon assisted diversified reaction of a β-silylmethylene malonate with dimethylsulfoxonium methylide

Reaction of dimethylsulfoxonium methylide with a β-silylmethylene malonate gives diversified products, cyclopropane, cyclobutane or allyl and homoallyl silanes depending upon the stoichiometry of the reactants and reaction conditions. Contrary to this, reaction of a β-arylmethylene malonate gives only the cyclopropane product. The product(s) formed are unique and the silicon group played a crucial role either by assisting and/or by participating in the process.     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for acetal formation

Commercially available copper(II) tetrafluoroborate hydrate has been found to be a highly efficient catalyst for dimethyl/diethyl acetal formation in high yields from aldehydes and ketones by reaction with trimethyl/triethyl orthoformate at room temperature and in short period. Acetalisation was carried out under solvent-free conditions with electrophilic aldehydes/ketones. For weakly electrophilic aldehydes/ketones (e.g., benzaldehyde, cinnamaldehyde and acetophenone) and for aldehydes having a substituent that can coordinate with the catalyst, the corresponding alcohol was used as solvent.     

多酯基取代的叶绿素类二氢卟吩衍生物的合成

以脱镁叶绿酸-a甲酯为起始原料,通过碱性条件下的水解开环、空气氧化和重排反应,分别合成了红紫素-7三甲酯和二氢卟吩-p6三甲酯.然后对其C(3)-乙烯基、20-meso-位、12-位甲基以及尾端酯基进行化学修饰,通过亲电加成、亲电取代、1,3-偶极环加成和氧化重排等反应,完成10种具未见报道的的叶绿素类二氢卟吩衍生物,其化学结构均经UV,IR,1H NMR光谱及元素分析予以表征.     

Synthesis of Potentially Biologically Active 6‐(1,3‐Butadiynyl)purines

1,3‐Alkadiynyl(trimethyl)silanes were prepared by the Negishi or Sonogashira reactions of bromoethynyl(trimethyl)silane with several terminal alkynes in 34–75% yield. However, the direct Hiyama coupling of these compounds with 6‐iodopurine derivatives has not been successful. Therefore, a modified Sonogashira reaction using TBAF or CsF for in situ removal of the trimethylsilyl group has been utilized. This methodology afforded the desired 6‐(1,3‐butadiynyl)purines in 47–87% yield.     

Direct synthesis of trimethyl(2-phenoxyethyl)silanes from aromatic fluorides

A direct synthesis of trimethyl(2-phenoxyethyl)silanes from the corresponding aromatic fluorides and 2-(trimethylsilyl)ethanol was developed. A variety of substituents were tolerated and a substitution reaction using 1-bromo-3-chloro-5-fluorobenzene was demonstrated.     

The polymerization of 3-chloro-1-propyne and 3-bromo-1-propyne with Mocl5 and WCL6 based initiators and the structure of the resulting polymers

The WCl₆ and MoCl₅ initiated polymerizations of 3-chloro-1-propyne and 3-bromo-1-propyne were performed in both halogenated and aliphatic non-nucleophilic and in aromatic nucleophilic solvents. The structure of the obtained polymers suggested that the polymerization reaction occurs in two steps. In both nucleophilic and non-nucleophilic solvents, the first step consists of the metathesis polymerization of 3-chloro(bromo)-1-propyne followed by electrophilic cis–trans isomerization leading to polymers containing trans-cisoidal allyl chloride or bromide structural units. When the polymerization is performed in non-nucleophilic solvents, in the second step an intramolecular electrophilic addition followed by elimination takes place. The resulting polymers contain a highly conjugated cyclopentadiene ladder structure. When the polymerization is performed in nucleophilic aromatic solvents, the intramolecular electrophilic addition competes with the electrophilic substitution of the solvent resulting in polymers containing high concentrations of arylpropenyl structural units. Subsequently, depending on the nucleophilicity of the polymerization solvent, the polymer structure contains structural units based on cyclopentadiene and/or arylpropenyl groups.     

Sc(OTf)3催化δ⁃腈基对亚甲基苯醌的1,6⁃共轭烯丙基化: 烯丙基二芳基乙腈类化合物的合成

将三氟甲烷磺酸钪[Sc(OTf)₃]用于催化δ-腈基-δ-芳基取代的对亚甲基苯醌与烯丙基硅烷的1,6-共轭加成反应, 快速制备了一系列含有四级碳中心的烯丙基取代二芳基乙腈类化合物. 该反应操作简单、 条件温和, 具有了良好的底物范围和官能团兼容性, 同时腈基和烯丙基可进行后期衍生化, 展示出良好的适用性.     

Ethylenic acyl cyanides I.: conjugate addition of allyl and allenylsilanes to ethylenic acyl cyanides.

δ,ε-Ethylenic (or acetylenic) acyl cyanides, or δ,ε-ethylenic (or acetylenic) acids and their methyl esters, can be obtained by a conjugate addition of allyl (or allenyl) silanes to α,β-ethylenic acyl cyanides.     

Fluoride ion induced reactions of organosilanes with electrophiles

Benzyl- 4-picolyl- and phenylallyl(trimethyl)silanes react with electrophiles in the presence of KF/18-crown-6 or silica-TBAF under mild conditions.     

Synthesis,Spectra Characterization,Electrochemical Behavior of Silyl Derivatives of Ferrocene

Ferrocenyl‐substituted silanes via the reaction between mono and dilithio‐ferrocene with trimethyl, trietheyl, vinyldimethyl or t‐butyldimethyl chlorosilanes is prepared. The electrochemical behaviors of these compounds were investigated by cyclic voltammetry. This work describes the electrochemical and electrocatalytic properties of carbon ceramic electrode (CCE) modified with ferrocene composites as a new electrocatalyst material.     

Allyl sulfones as precursors to allylzincs in the palladium-catalyzed zinc-ene cyclization: highly efficient synthesis of enantiopure (-)-erythrodiene

Easily prepared allyl phenyl sulfones, capable of introduction of the alkene by electrophilic alpha-substitution, are superior to allyl acetates as substrates for Pd-catalyzed Zn-ene cyclizations, providing C5 or C(4)N rings with cis-1,2-vinyl and -CH(2)Zn substituents. Several examples, with different methods of substrate preparation, are presented. [reaction: see text]     

An efficient preparation of new sulfonyl fluorides and lithium sulfonates

An efficient preparation of several polyfluoroalkanesulfonyl fluorides is reported. This method, based on the synthesis of polyfluoroalkyl trimethyl silanes (precursors of polyfluoroalkylsulfinates) as intermediates, allows the successive transformations to be carried out in one pot. Moreover, these sulfonyl fluorides can be obtained from the corresponding sulfinates by electrophilic fluorination. This original approach avoids isolation and purification of some thermally or hydrolytically unstable intermediates. A series of new sulfonyl fluorides have been thus prepared from halogenodifluoromethylated precursors RCF2X (X = F, Br; R = ArC(O), ArS(O)n(CF2)m; n = 0, 1, 2; m = 1, 2) and have been transformed into the corresponding lithium sulfonates, which have potential applications as electrolytes for lithium batteries.