Improved dielectric properties of poly(vinylidene fluoride)–BaTiO3 composites by solvent-free processing

Composites of poly(vinylidene fluoride) (PVDF) and BaTiO₃ nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent-free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·10⁴ Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents.     

Lewis Acid‐Catalyzed Generation of C?C and C?N Bonds on π‐Deficient Heterocyclic Substrates

Focused microwave irradiation of a series of halogenated nitrogen heterocycles and different kinds of nucleophiles in the presence of a catalytic amount of indium trichloride leads to the efficient and completely regioselective generation of aromatic C C and C N bonds. The method is simple, rapid, general and inexpensive, and can be performed without the use of dried solvents. Most of the synthetized compounds are new and in many cases the work‐up required only filtration. Furthermore, this is the first example of the use of a Lewis acid as a catalyst for heteroarylation, vinylation and amination reactions on π‐deficient heterocyclic substrates.

     

Copper‐Catalyzed Synthesis of α‐Thioaryl Carbonyl Compounds Through S?S and C?C Bond Cleavage

A method to access α‐thioaryl ketones and α‐thioaryl esters employing copper acetate (hydrate) as catalyst and readily accessible diaryl disulfides and β‐diketones (or β‐keto esters) has been developed. Both alkyl‐ and aryl‐substituted carbonyl compounds can be prepared.

     

Rhodium(III)‐Catalyzed C(sp2)?H Activation and Electrophilic Amidation with N‐Fluorobenzenesulfonimide

An electrophilic amidation via a cationic rhodium(III)‐catalyzed C(sp²) H activation has been developed with the commercially available N‐fluorobenzenesulfonimide as the amino source under external oxidant‐free conditions. This amidation requires only a catalytic amount of base and exhibits excellent functional group tolerance and regioselectivity, providing a new avenue in direct C(sp²) H amidation.     

Palladium‐Catalyzed Decarboxylative Coupling of α‐ Oxocarboxylic Acids with C(sp2)?H of 2‐Aryloxypyridines

An efficient palladium‐catalyzed decarboxylative ortho‐acylation of 2‐aryloxypyridines with α‐oxocarboxylic acids is described. In this new transformation, the aromatic C(sp²) H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding 2‐hydroxy aromatic ketones.     

Cadmium(II)‐Catalyzed C?N Cross‐Coupling of Amines with Aryl Iodides

Cadmium diacetate dihydrate [Cd(OAc)₂⋅2 H₂O] in combination with ethylene glycol catalyzes efficiently the C N cross‐coupling of amines with aryl iodides by a benzyne mechanism. Alkyl, aryl and heterocyclic amines are compatible with this system affording the aminated products in high to excellent yield.     

Visible Light‐Initiated C(sp3)?Br/C(sp3)?H Functionalization of α‐Carbonyl Alkyl Bromides through Hydride Radical Shift

A new visible light‐initiated 1,5‐hydride radical shift strategy has been developed to enable the one‐step functionalization of both a C(sp³) Br bond and a C(sp³) H bond adjacent to the same carbon atom. This visible light photoredox catalysis offers a mild and straightforward access to diverse five‐membered carbocyclic ring‐fused polycyclic hydrocarbons with high turnover numbers (TONs; up to 4.93×10³) and broad substrate scope.

     

Iridium(III)‐Catalyzed Direct C?H Sulfonamidation of 2‐Aryl‐1,2,3‐triazole N‐Oxides with Sulfonyl Azides

We have developed a method for the direct sulfonamidation of 2‐aryl‐1,2,3‐triazole N‐oxides using sulfonyl azides as the amino source to release molecular nitrogen as the sole by‐product. This protocol exhibits excellent functional group tolerance and proceeds efficiently under external oxidant‐free conditions. Various 2‐(2‐sulfonamidoaryl)‐1,2,3‐triazoles were prepared in up to 97% yields for 25 examples with excellent regioselectivity.

     

Diruthenium(I,I) Catalysts for the Formation of β‐ and γ‐Lactams via Carbenoid C?H Insertion of α‐Diazoacetamides

Intramolecular carbenoid C H insertion of five α‐diazoacetamides [N₂CH CONR₂, NR₂=NEt₂ ( 3a ), NBu₂ ( 3b ), N(i‐Pr)₂ ( 3c ), N(CH₂Ph)₂ ( 3d ), N(i‐Pr)(CH₂Ph) ( 3e )], was investigated using as catalysts dinuclear Ru(I,I) complexes of the type [Ru₂(μ‐L¹)₂(CO)₄L²₂], where L¹ is a bidentate bridging acetate, calix[4]arenedicarboxylate, saccharinate, pyridin‐2‐olate, or triazenide ligand, as well as [RuCl₂(p‐cymene)]₂. The Ru(I,I) complexes were found to be suitable catalysts for the carbenoid cyclization reactions, except in the case of 3a . With diazoamides 3b–e , [Ru₂(μ‐sac)₂(CO)₅]₂ (sac=saccharinate) and [Ru₂(μ‐6‐chloropyridin‐2‐olate)₂(CH₃CN)₂(CO)₄] are as effective as Rh₂(OAc)₄ under the same conditions, although some differences in the regioselectivity and chemoselectivity of the cyclization are observed. The carbenoid cyclization reactions yield γ‐lactams from diazoamides 3a and 3b , both a β‐ and a γ‐lactam from 3c , and a β‐lactam as well as a 3‐azabicyclo[5.3.0]deca‐5,7,9‐trien‐2‐one from 3d . With 3e , formation of γ‐lactam 21 and of bicyclic lactam 23 prevails.     

Crystallization kinetics of γ phase poly(vinylidene fluoride)(PVDF) induecd by tetrabutylammonium bisulfate

The phase transition behavior of poly(2-ethyl-2-oxazoline) (PEtOx) under complexation with star-shaped poly(acrylic acid) (PAA) having various arm numbers (two, three, four, and six) has been studied by turbidity and laser light scattering measurements. The change in cloud point temperature (T _cp) of PEtOx was monitored as a function of pH, ionic strength, and arm number of the star polyelectrolyte. The shift in T _cp to a lower value than that of pure PEtOx was more pronounced at pH 4.2 (pH?a), when the carboxylic acid groups are protonated as compared to pH 7.0 (pH?>?pK_a ), when the acid moieties are partially ionized. Dynamic light scattering showed that these complexes may have micellar core-shell type structure with a mean hydrodynamic radius (R _h) ranging from 12 nm to ～200 nm depending upon the temperature. Significant shift in T _cp was observed for six-arm star poly(acrylic acid) complexes at both pH values. This change in the T _cp is accredited to the differences in the driving forces of phase transition, including hydrogen bonding between carboxylic acid groups of PAA and the carbonyl moiety of PEtOx as well as the hydrophobic interactions.     

Nickel‐Catalyzed α‐Benzylation of Arylacetonitriles via C?O Activation

Efficient Ni‐catalyzed direct cross‐couplings of benzylic alcohol derivatives with arylacetonitriles via C O activation are described. Various α‐benzylated arylacetonitriles including those with functional groups can be prepared under mild reaction conditions.

     

Easy Access to 1‐Amino and 1‐Carbon Substituted Isoquinolines via Cobalt‐Catalyzed C?H/N?O Bond Activation

A green atom‐economical method for the synthesis of highly functionalized 1‐amino and 1‐carbon substituted isoquinolines from the reaction of N′‐hydroxybenzimidamides and aryl ketoximes, respectively, with alkynes via pentamethylcyclopentadienylcobalt(III)‐catalyzed C H/N O bond activation is described. The external oxidant‐free annulation reaction uses the =NOH moiety in N′‐hydroxybenzimidamides or N‐aromatic ketone oximes as the directing group and internal oxidant. This first row transition metal‐catalyzed annulation serves as an efficient alternative for the synthesis of isoquinolines, as water is the only by‐product and expensive noble metals such as rhodium(III), iridium(III), palladium(II), and ruthenium(II) are not required. The reaction proceeds via C H activation, alkyne insertion, reductive elimination, and N O activation.

     

Synthesis of Isoquinolines via Rhodium(III)‐Catalyzed Dehydrative C?C and C?N Coupling between Oximines and Alkynes

Isoquinolines have been synthesized from the redox‐neutral dehydrative C N and C C cross‐coupling between oximines and alkynes using a catalytic amount of (pentamethylcyclopentadiene)rhodium dichloride dimer {[RhCp*Cl₂]₂} and cesium acetate (CsOAc), a process that involves ortho C H activation of oximines and subsequent functionalization with alkynes. This redox‐neutral catalytic isoquinoline synthesis operates under mild conditions, and is insensitive to moisture or air. A broad scope of coupling partners has been established, and a likely mechanism has been suggested.     

Rhodium(III)‐Catalyzed Direct C?H Olefination of Arenes with Aliphatic Olefins

A rhodium(III)‐catalyzed direct ortho C H bond olefination of arenes, including but not limited to benzamides, arylpyridines and indoles, with a variety of unactivated aliphatic olefins has been developed. In the presence of catalytic amounts of dichloro(pentamethylcyclopentadienyl)rhodium(III) dimer {[Cp*RhCl₂]₂}, copper(II) acetate monohydrate [Cu(OAc)₂⋅H₂O] and silver hexafluoroantimonate(V) (AgSbF₆), the coupling reaction occurred efficiently to afford the ortho‐olefinated linear products in good to excellent yields with high regio‐ and stereoselectivities, and a range of functional groups in both coupling partners is compatible with the reaction conditions. This protocol relies on the use of directing groups, and the addition of AgSbF₆ as additive is crucial for the catalysis. This new method expands the scope of rhodium(III)‐catalyzed direct C H bond olefination of arenes, and provides a rapid access to useful linear arylation products of unactivated olefins.

     

Organocatalytic Asymmetric C?S Bond Formation: Synthesis of α‐Methylene‐β‐mercapto Esters with Simple Alkyl Thiols

A highly efficient organocatalytic enantioselective C S bond formation reaction between simple alkyl thiols and Morita–Baylis–Hillman (MBH) carbonates is described. The optically active α‐methylene β‐mercapto esters could be obtained under mild reaction conditions with excellent enantioselectivities (up to 97% ee). The broad scope and simple operation make this methodology very practical.     

Synthesis of 3‐Aryl‐1‐trifluoromethyltetrahydroisoquinolines by Brønsted Acid‐Catalyzed C(sp3)?H Bond Functionalization

A concise route to 3‐aryl‐1‐trifluoromethyltetrahydroisoquinolines by a benzylic [1,5]‐hydride shift‐mediated C H bond functionalization was developed. The [1,5]‐hydride shift of the benzylic C(sp³) H bond to the trifluoromethylketimine derived from para‐anisidine occurred smoothly to produce cis‐1‐trifluoromethyl‐3‐aryltetrahydroisoquinolines in good to excellent chemical yields with good diastereoselectivities. In contrast, use of the N H ketimine furnished N‐unprotected tetrahydroisoquinolines in good yields in favor of the trans‐isomer.

     

An Indium(III)‐Catalyzed Synthesis of 4,4‐Dichloro‐1‐aryl‐N‐alkyl‐1‐yn‐3‐amines via an Intermolecular C(sp2)?C(sp) Bond Formation

This paper demonstrates an indium(III) triflate‐catalyzed reaction of electron‐deficient α,α‐dichloroaldimines with terminal alkynes leading to a rapid and selective access to highly functionalized propargylic amines in good to excellent yields. The dichloromethylene moiety of the aldimine acts as an activating group to accomplish this transformation under very mild conditions.     

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric C?C Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

The enzymes benzaldehyde lyase (BAL) from Pseudomonas fluorescens, benzoylformate decarboxylase (BFD) from Pseudomonas putida and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae provide different C C bond forming possibilities of α,β‐unsaturated aldehydes with aliphatic and aromatic aldehydes. Structure elucidation and determination of the absolute configuration of the products, which were obtained with high regio‐ and stereoselectivity were carried out. Selective 1,2‐reactivity with yields of 75% and >98% ee, for one single isomer ( A ) were obtained, by choosing the suitable enzyme in combination with the appropriate substrates. By varying enzymes or substrates the regioisomeric hydroxy ketones C , with up to >99% ee, can be obtained. The application of these new chiral building blocks in the synthesis of natural products or biological active substances is considerably facilitated by applying the different ThDP‐dependent enzymes as catalysts. Abbreviations: BAL, benzaldehyde lyase; BFD, benzoylformate decarboxylase; PDC, pyruvate decarboxylase; His, hexahistidine; 2‐HPP, 2‐hydroxy‐1‐phenylpropan‐1‐one; PAC, phenylacetylcarbinol; NTA, nitrilotriacetic acid; ThDP, thiamin diphosphate; wt, wild‐type.     

Design and Synthesis of 2‐Methyl‐7‐aminobenzoxazole as Auxiliary in the Palladium(II)‐Catalyzed Arylation of a beta‐Positioned C(sp3)?H Bond

A palladium(II)‐catalyzed direct arylation of methylene C(sp³) H bonds by 2‐methyl‐7‐aminobenzoxazole as an effective auxiliary is reported. This process exhibited high beta‐site selectivity, broad substrate scope, and compatibility with different functional groups with moderate to high yields up to 89%.

     

High‐Valent Pentamethylcyclopentadienylcobalt(III) or ‐iridium(III)‐Catalyzed C?H Annulation with Alkynes: Synthesis of Heterocyclic Quaternary Ammonium Salts

Nine types of diversely fused heterocyclic quaternary ammonium salts were constructed through an oxidative C H annulation reaction. Both high‐valent pentamethylcyclopentadienylcobalt(III) and pentamethylcyclopentadienyliridium(III) were found to be effective as catalyst for this reaction. Broad substrate scope and good functional group tolerance were observed.