2-(Fluorophenyl)pyridines by the Suzuki-Miyaura method: Ag2O accelerates coupling over undesired ipso substitution (SNAr) of fluorine

Problematic ipso substitution was observed in the Suzuki-Miyaura coupling of pentafluorophenylboronic acid to make 2-pentafluorophenylpyridine. Strong bases favored coupling, but under these conditions fluorine in the product tended to undergo nucleophilic substitution. Inclusion of Ag₂O accelerated coupling over ipso substitution.     

An efficient intermolecular BINAM-copper(I) catalyzed Ullmann-type coupling of aryl iodides/bromides with aliphatic alcohols

A wide range of alkyl aryl ethers are synthesized from the corresponding aryl iodides and aliphatic alcohols through Ullmann-type intermolecular coupling reactions in the presence of a catalytic amount of easily available BINAM-CuI complex. Less reactive aryl bromides have also been shown to react with aliphatic alcohols under identical reaction conditions to give good yields of the alkyl aryl ethers without increasing the reaction temperature and time.     

Efficient oxidative ipso-fluorination of para-substituted phenols using pyridinium polyhydrogen fluoride in combination with hypervalent iodine(III) reagents

Diacetoxyiodobenzene (PIDA) and bis(trifluoroacetoxy)iodobenzene (PIFA) in the presence of pyridinium polyhydrogen fluoride (PPHF) are effective for the fluorination of para-substituted phenols to give a variety of 4-fluorocyclohexa-2,5-dienones in a good yield. (R,S)-1,1′-Bi-5,6,7,8-tetrahydro-2-naphthol (and its monoacetate) yields atropoisomeric fluorocyclohexadienones. The 4-substituted carbamate open-chain phenols were readily converted to fluorohydroindolenone and fluorohydroquinolenone derivatives by intramolecular conjugate addition.     

1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 2: Synthesis of trifluoromethyl substituted thiophenes, condensed with cyclobutene moieties

This paper describes a novel synthetic approach to 2-cyano-3-trifluoromethylthiophenes fused with cyclobutene rings with variable spiro conjunctions. The reaction of substituted 1-bromo-2-trifluoroacetylcyclobutenes with mercaptoacetonitrile results in the substitution of bromine with S-center to afford the corresponding nitriles in high yields, which form the target thiophenes by subsequent treatment of lithium 2,2,6,6-tetramethylpiperidide and acetic anhydride.     

Acceleration of CuI-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents using lithium chloride

In the presence of LiCl, CuI-catalyzed coupling reaction of R(alkyl)-X with Ar(aryl)MgBr at rt was completed within 2 h. Effective leaving groups X in R-X were Br, I, OTs, but not Cl. Grignard reagents ArMgBr with both standard and bulky Ar such as 2-MeC₆H₄, 2-MeOC₆H₄, and 2,6-(Me)₂C₆H₃ afforded the desired products in good yields. Ester and cyano groups in R-X were tolerated. Coupling reaction with R(alkyl)-MgBr proceeded as well.     

Practical preparation of methyl vinyl ethers through the direct coupling of ketones with CHCl2OMe promoted by Mg/TiCl4/THF

Herein we utilized a new methylene carbenoid as an extremely simple and highly practical reagent for the preparation of vinyl ether with good to excellent yield. This method efficiently effects methoxymethylenation or vinyl ether formation of enolizable, nonenolizable, and sterically hindered ketones. The complexation of Ti–Mg–CHOMe was facilitated, presumably, by THF dramatically increasing the feasibility; and scope of this protocol is to produce vinyl ethers which can be used as convenient building blocks for the preparation of biologically useful molecules.     

Effect of electron-withdrawing power of the substituted group on?OH radical reaction with substituted aryl sulphides: A pulse radiolysis study

In neutral aqueous solution of (phenylthio)acetic acid, hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 × 10^-1 dm³ mol⁻s⁻ and the transient absorption bands are assigned to^•OH radical addition to benzene and sulphur with a rough estimated values of 50 and 40% respectively. The reaction of the^•OH radical with diphenyl sulphide (k = 4.3 × 10⁸ dm³ mol⁻¹ s⁻¹) is observed to take place with formation of solute radical cation, OH-adduct at sulphur and benzene with estimated values of about 12, 28 and 60% respectively. The transient absorption bands observed on reaction of^•OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λ_max = 550 and 730 nm), OH-adduct at sulphur (λ_max = 360 nm) and addition at benzene ring (λ_max = 320 nm). The fraction of^•OH radical reacting to form solute radical cation is observed to depend on the electron-withdrawing power of substituted group. In acidic solutions, depending on the concentration of acid and electron-withdrawing power, solute radical cation is the only transient species formed on reaction of^•OH radical with the sulphides studied.     

Unusual dimerization of N-protected bromomethylindoles/benzyl bromide with arylmetal halides: generation of indolylmethyl/benzyl radical

A detailed study on the interaction of N-protected bromomethylindoles with various types of aryl/alkyl Grignard is reported. Full experimental details on the mechanism of the unusual dimerization reaction are presented.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units: I. Synthesis and characterization

A series of novel wholly aromatic polyamide-hydrazides was synthesized by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl chloride (TCl), isophthaloyl chloride (ICl), or mixtures of various molar ratios of TCl and ICl in anhydrous N,N-dimethylacetamide (DMAc) as a solvent. Polymer structures were identified by elemental analysis and infrared spectroscopy. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The content of para- and meta-phenylene moieties was varied within this series so that the changes in the latter were 10 mol % from polymer to polymer, starting from an overall content of 0-100 mol %. The prepared polymers were characterized for their properties in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as solubility, intrinsic viscosity, moisture regain, mechanical properties and thermal as well as thermo-oxidative stability. The polymers were readily soluble in several organic polar solvents such as DMAc, N,N-dimethylformamide, dimethyl sulphoxide, N-methyl-2-pyrrolidone and hexamethyl phosphoramide and could be cast into flexible films. Their solubilities were found to increase remarkably with introduction of meta-phenylene moieties into the polymer chains. Their intrinsic viscosities ranged from 0.73 to 4.83 dl g⁻¹ in DMAc at 30 °C and increased with the increase of para-phenylene units content. Mechanical properties of the films produced from these polymers are improved markedly by substitution of para-phenylene units for meta-phenylene units. Thermogravimetric studies revealed that the completely para-oriented type of polymer has better thermal and thermo-oxidative stability relative to that of the other polymers. Moreover, the results reveal that the prepared polymers have a great affinity to water sorption. The hydrophilic character increases as a function of meta-oriented phenylene rings incorporated into the polymer chains.     

Copper-catalyzed cascade coupling/cyclization of terminal alkynes with diazoacetates: a straightforward route for trisubstituted furans

A copper-catalyzed cascade coupling/cyclization of terminal alkynes with α-alkyl substituted diazoesters is developed. This new method furnished a straightforward route for 2,3,5-trisubstituted furan derivatives with good efficiency and selectivity.     

Copper/oxalohydrazide/ketone catalyzed synthesis of primary arylamines via coupling of aryl halides with aqueous ammonia in water

The coupling reaction of aryl halides with aqueous ammonia was catalyzed by copper/oxalohydrazide/ketone system in water to yield primary arylamines without inert atmosphere. This method was fast and facile. The coupling reaction proceeded at 90 °C for 20-80 min, or at room temperature for a prolonged reaction time. A variety of aryl bromides and iodides were found to be applicable to this three-component catalytic system, which afforded good to excellent isolated yields.     

Effects of coupling agents on mechanical and morphological behavior of the PP/HDPE blend with two different CaCO3

The main purpose of incorporating fillers, such as calcium carbonate, into blends of polyolefins is to decrease costs and change tensile and impact properties. Structural differences between both components give rise to the formation of large filler agglomerates in the polymer matrix, which influence the mechanical response of the material. Therefore, the coupling agents of the Lica 12 type at various concentrations was used to facilitate the link between filler and matrix (the latter consisting of PP/HDPE 80/20 wt). Filler was added to the PP/HDPE blend at a 30 wt.% concentration. Two types of calcium carbonate (CaCO₃) were used. These have different average sizes (3.0 and 1.8 μm) which were determined by means of laser diffraction techniques. In addition other coupling agents of the titanate type, such as Lica 09, Lica 01, zirconates ZN 12, and a 1:1 mixture of Lica 12 and Lica 01, were used. This study clearly demonstrated that the addition of the coupling agent to CaCO₃ modifies the mechanical properties of the PP/HDPE/CaCO₃ composites. Values of the mechanical properties indicate that due to its characteristics, each coupling agent gives rise to increases in a particular mechanical property. In the case of Lica 01 an increase was verified in Young’s modulus at 0.7 wt.% and in elongation at break at both concentrations (0.3 and 0.7 wt.%), whereas ZN 12 brought about an increase in elongation at break. The 1:1 mixture of Lica 12 and Lica 01 caused impact resistance of the blend of PP/HDPE with CaCO₃ to increase considerably.     

Facile conversion of para-benzoquinones to para-alkoxyphenols with primary/secondary alcohols and amberlyst-15: a process showing novel reducing property of such alcohols

A new efficient methodology has been developed for the synthesis of para-alkoxyphenols, an important group of anti-melanoma compounds, by heating alcoholic solutions of para-benzoquinones in the presence of amberlyst-15. The most notable feature here is the behaviour of the used primary or secondary alcohol as an effective reducing agent.     

para-Sulfonatocalix[6]arene-modified silver nanoparticles electrodeposited on glassy carbon electrode: Preparation and electrochemical sensing of methyl parathion

In this paper, a new electrochemical sensor, based on modified silver nanoparticles, was fabricated using one-step electrodeposition approach. The para-sulfonatocalix[6]arene-modified silver nanoparticles coated on glassy carbon electrode (pSC₆-Ag NPs/GCE) was characterized by attenuated total reflection IR spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), etc. The pSC₆ as the host are highly efficient to capture organophosphates (OPs), which dramatically facilitates the enrichment of nitroaromatic OPs onto the electrochemical sensor surface. The combination of the host-guest supramolecular structure and the excellent electrochemical catalytic activities of the pSC₆-Ag NPs/GCE provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs. In this work, methyl parathion (MP) was used as a nitroaromatic OP model for testing the proposed sensor. In comparison with Ag NPs-modified electrode, the cathodic peak current of MP was amplified significantly. Differential pulse voltammetry was used for the simultaneous determination of MP. Under optimum conditions, the current increased linearly with the increasing concentration of MP in the range of 0.01-80 μM, with a detection limit of 4.0 nM (S/N = 3). The fabrication reproducibility and stability of the sensor is better than that of enzyme-based electrodes. The possible underlying mechanism is discussed.     

Highly regio- and stereoselective PdCl2(MeCN)2-catalyzed cross coupling of 1,2-allenylic sulfoxides with allyl bromide

2-Allyl-1(E),3(E)-dienyl sulfoxides were prepared highly stereoselectively via the PdCl₂(MeCN)₂-catalyzed coupling reaction of 1,2-allenylic sulfoxides and allyl bromide. A rationale was proposed for this transformation.     

Intramolecular alkene Friedel-Crafts cyclization of 1-allyl-1-N-(ortho-alkylphenylamino)cyclohexanes. A useful route to alkyl substituted dihydrospiro[(1H)quinoline-2,1-cyclohexanes]. Unprecedented ipso-substitution of alkyl groups

An unprecedented intramolecular Friedel-Crafts ipso-alkylation at the ortho-alkyl group of the N-arylamino moiety of 1-allyl-1-N-arylaminocycloalkanes to give alkyl substituted dihydrospiro[(1H) quinoline-2,1^′-cycloalkanes] is reported. Unexpected results were explained in the context of intramolecular ipso-substitution of alkyl groups and their 1,2-rearrangement. A plausible mechanism for this type of Friedel-Crafts alkylation by an alkene moiety promoted by a Brönsted acid (H₂SO₄) is proposed.     

Unusual anomeric rearrangement of para-nitrobenzoylxanthate d-glycosides: a new direct stereoselective access to α-thioglycosides from pyranose sugars

A mild and general procedure for the synthesis of α-thioglycosides from glycopyranoses is described. The method involves the treatment of pyranose reductive sugar with sodium hydride, carbon disulfide, and p-nitrobenzoyl chloride, as a key step, to yield p-nitrobenzoyl-α-d-thioglycopyranose intermediates with high stereoselectivity, in a one-pot-two-step process. The interest of the strategy highlights a direct stereoselective access to ether-protected 1-thiol-α-d-glycopyranose derivatives (Gal, Glc, and Man) from pyranoses in the absence of anomeric ‘Lewis acid’ promoters.     

Palladium-catalyzed coupling of N-tosylhydrazones with ortho substituted aryl halides: synthesis of 4-arylchromenes and related heterocycles

A convenient and efficient procedure for the synthesis of 4-arylchromenes, thiochromenes, and related heterocycles via a four step-sequence has been developed. The first three steps, which involve hydration of alkynes, hydrazones formation, and their Pd-coupling with ortho substituted aryl halides, furnished stereoselectively Z-trisubstituted olefins without any purification of the intermediates generated in each stage. These latter proved to be suitable precursors, in the last step, for the synthesis of the desired heterocycles of biological interest.     

Palladium mediated direct coupling of silylated arylalkynes with propargylic chlorides: an efficient access to functionalized conjugated allenynes

Pd/Cu-catalyzed one-pot reaction of 1-trimethylsilyl-2-arylalkynes with propargylic chlorides in the presence of TBAF is described. The present new procedure is applicable to a wide range of silylated arylalkynes with both electron-withdrawing and electron-donating substituents. Functionalized allenynes can thus be obtained in good yields without prior deprotection of the alkynes.