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Four families of structurally related chiral π‐conjugated oligomers bearing a hydroquinone (HQ), 1,5‐dihydroxynaphthalene (Naph), benzo[1,2‐b:4,5‐b']dithiophene‐4,8‐diol (BDT) or 9H‐carbazole (CBZ) central core, for a total of 11 new compounds, have been synthesized by simple and versatile synthetic strategies involving Pd‐catalyzed cross‐coupling protocols: a Suzuki‐Miyaura reaction, a Sonogashira/desilylation/Sonogashira sequence or a Sonogashira/desilylation/acyl Sonogashira sequence. A systematic investigation of the optical and chiroptical features of the final chiral dyes was performed in chloroform solution and on spin‐coated thin films. The ECD investigation was crucial in revealing that, even within the same family of organic dyes, minor variations in the nature and length of the π‐conjugated backbone can result in very different solid‐state arrangements at different hierarchical scales. [ABSTRACT FROM AUTHOR]

Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photonics and spintronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self‐assembled thin film made of a carbazole di‐bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure–property relationships, resulting in a more efficient material design. [ABSTRACT FROM AUTHOR]

In this work, we synthesized a family of three structurally related chiral oligothiophenes containing a 1,4‐diketo‐3,6‐diarylpyrrolo[3,4‐c]pyrrole (DPP) unit as the central core; functionalized with the same (S)‐3,7‐dimethyl‐1‐octyl chains on the nitrogen atoms of lactam moieties, they only differ in the number of lateral thiophene units. The aggregation modes of these π‐conjugated chiral systems were evaluated by means of UV–Vis absorption and ECD spectroscopies in conditions of solution aggregation (CHCl3/MeOH mixtures) and as thin films, describing in particular the impact of the π‐conjugation length on the chiroptical properties. Interestingly, we found that the variable number of thiophene units attached to the DPP core affects not only the propensity to aggregation but also the aggregates' helicity. ECD revealed information about the supramolecular arrangement of these molecules, that one would not obtain by using conventional optical spectroscopy and microscopy techniques. Thin film samples revealed very different aggregation modes with respect to solution aggregates, casting doubts on the common assumption that these latter may serve as simple models of the former ones. [ABSTRACT FROM AUTHOR]

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects. [ABSTRACT FROM AUTHOR]

The synthesis of chiral 3-atyl-1-alkynes via cross coupling of 3-alkyl- and 3,3-diaalkyl-1-bromo-1,2-dienes and arylbromocuprates (RCuBr)MgBr.LiBr was examined. The high 1,3-anti stereoselectivity of the coupling process helped in obtaining enantiomerically enriched 3-aryl-1-alkynes from optically active allenic substrates, thus indicating a simple pathway towards the synthesis of quaternary stereogenic centers characterized by an aryl group.

Research has been conducted on the rhodium-catalyzed intramolecular silylformylation of substituted omega-silylacetylenes. Results indicate its considerable organic synthesis potential.

After the optimization of the reaction sequence under batch conditions, the carbonylation reactions were performed also in a flow rector that provided the desired bicyclic lactones in comparable yields to standard batch conditions. Oxygen and nitrogen heterocycle systems are found in a vast number of natural substrates and biologically active molecules such as antimycotics, antibiotics, antitumors and antioxidants, in addition to pigments and fluorophores. [Extracted from the article]

This work reports the first observation of circularly polarized electroluminescence (CPEL) in thin films of self‐organized oligothiophenes. Four new 1,4‐phenylene and 9H‐carbazole‐based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthesized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed glum in the order of 10−2 on a wide wavelengths range, originating from their self‐organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularly‐polarized organic light‐emitting diodes (CP‐OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP‐OLED with active layer made only of a small organic compound. [ABSTRACT FROM AUTHOR]

An attempt is made to consider a new methodology towards 2-(arylmethyl)aldehydes, which is based upon 1,2-anionotropic rearrangement of an aryl group. Further, the experimental conditions of the fluoride-promoted step and the synthetic potentialities of the process are described.

Abstract: A chiral benzo[1, 2‐b:4,5‐b′]dithiophene‐based oligothiophene with the very uncommon chiroptical property of signal inversion on sample flipping was recently described. This property is due to the interference between linear dichroism and linear birefringence, called LDLB effect, which is theoretically well understood, but to date very rarely reported in the literature. Samples with very large LDLB effect lead to the unique possibility of discriminating the direction of sample illumination (i. e., from the front or back). This article presents a set of analogue compounds, in which small structural changes are introduced to uncover which factors determine the very large LDLB effect or true circular dichroism connected to supramolecular chirality. It also reveals the impact of the deposition technique, in which spin coating may exert a primary role, and results in films with outstanding chiroptical features. These features are made even more relevant due to the semiconducting properties of oligothiophenes, which are interesting for optical sensing applications. [ABSTRACT FROM AUTHOR]

Oxygen and nitrogen heterocycles are present in a vast number of natural substrates and biologically active molecules. In particular, phthalan and isoindoline subunits are found in many classes of products such as antibiotics, antioxidants, antimycotics, pigments, and fluorophores. Therefore several procedures dedicated to the construction of these heterocycles have been developed. In this review, a detailed analysis of the literature data regarding the synthesis of these nuclei via cyclization reactions is reported. 1 Introduction 2 Phthalans 2.1 Oxa-Pictet--Spengler Reaction 2.2 Garratt--Braverman Cyclization 2.3 Diels--Alder and Related Reactions 2.4 [2+2+2] Cyclotrimerization of Alkynes 2.5 Cycloetherification of ortho-Substituted Aromatics 2.6 Tandem Carbonylative Sonogashira Coupling--Cyclization Reactions 3 Isoindolines 3.1 Amination of Dihalides 3.2 Intramolecular Hydroamination 3.3 Diels--Alder and Related Reactions 3.4 [2+2+2] Cycloaddition Reactions 3.5 Tandem Carbonylative Sonogashira Coupling--Cyclization Reactions 4 Conclusions [ABSTRACT FROM AUTHOR]

Oxygen and nitrogen heterocycle systems are found in a vast number of natural substrates and biologically active molecules. In particular, phthalan, isochroman, and isoindoline scaffolds are present in many classes of products such as antimycotics, antibiotics, antioxidants, pigments, and fluorophores. Therefore several procedure dedicated to the building of such heterocycles have been developed. In this review a detailed analysis of literature data relating to these scaffolds is described. Particular attention has been devoted to their biological and chemical potentiality, and an in-depth investigation into the most important synthetic methods is reported. Cyclocarbonylative Sonogashira coupling of suitable alcohols and amides has been carefully considered, because it represents a valuable and atom-economic route for the construction of alkylidenephthalans, -isochromans, and -isoindolines. [ABSTRACT FROM AUTHOR]

A new protocol for the synthesis of 3-isochromanone derivatives based on rhodium-promoted silylcarbocyclisation reactions of ethynylbenzyl alcohol with different arylsilanes is described. The structure of the isochromanone depends upon the reaction conditions used: when the reaction is carried out without base, ( Z)-4-[(aryldimethylsilyl)methylene]isochroman-3-ones are obtained as major products. These compounds can be submitted to a desilylation/aryl migration reaction to give 4-(arylmethyl)isochroman-3-ones in high yields. In contrast, in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), hydrogenation of methyleneisochroman-3-ones takes place, and the corresponding β-(silylmethyl)-3-isochromanones are formed. Moreover, when internal alkynes are treated with hydrosilanes under silylcarbocyclisation reaction conditions, alcoholysis of the hydrosilanes occurs exclusively. [ABSTRACT FROM AUTHOR]

A protocol based on cyclocarbonylative Sonogashira reactions has been developed for the synthesis of nitrogen-containing heterocycles. The process is carried out under CO pressure, in the presence of a small amount of PdCl2(PPh3)2 (0.2–0.4 mol-%) as a catalytic precursor, and without the need for a copper salt as cocatalyst. Suitable tosylamides reacted successfully with iodoarenes bearing electron-withdrawing and electron-donating groups. In particular, N-(2-ethynylbenzyl)-4-methylbenzenesulfonamide gave carbonylmethylene isoindolines with complete chemo- and stereoselectivity. On the other hand, the reaction between iodoarenes and N-(2-ethynylphenethyl)-4-methylbenzenesulfonamide did not yield tetrahydroisoquinolines as expected, but dihydrobenzoazepines were obtained. [ABSTRACT FROM AUTHOR]

In this work, we present a carbonylative Sonogashira reaction of o-ethynyl benzyl alcohols and aryl iodides, followed by a cyclization process to selectively give carbonylmethylene isobenzofurans in high yields and in an atom-economic fashion. The reaction can be carried out in the absence of CuI, with a small amount of PdCl2(PPh3)2 (0.2-0.5 mol-%), using aryl iodides bearing both electron-withdrawing and electron-donating groups. Of the two possible stereoisomeric products, Z-isobenzofuran derivatives were obtained as major products. But, when the reaction was extended to a secondary alcohol, an interesting switch in stereoselectivity was observed. [ABSTRACT FROM AUTHOR]

In this study we used a tandem carbonylative Sonogashira reaction/cyclisation process to construct alkylidene-functionalized isochromans in high yields with complete stereoselectivity (only Z isomers were formed). The reaction was performed in the absence of a CuI co-catalyst with a small amount of PdCl2(PPh3)2 (0.2-0.5 mol-%), and aryl iodides bearing both electron-donating and electron-withdrawing substituents were successfully employed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Palladium nanoparticles (Pd NP) prepared by means of metal vapour synthesis technique. [•] Deposition of Pd NP on Smopex® metal scavengers. [•] Pd/Smopex®-234 catalyses selectively carbonylative Sonogashira reactions. [•] Preliminary tests indicate a heterogeneous behaviour. [ABSTRACT FROM AUTHOR]

Abstract: Solvated platinum atoms, obtained by metal vapour synthesis (MVS), were conveniently used to prepare γ-iron oxide and γ-alumina supported Pt catalysts containing small metal nanoparticles of controlled size, ranging 0.5–3.0nm in diameter (HR-TEM). The γ-Fe2O3-supported Pt system showed higher catalytic activity and selectivity than those of a similarly prepared γ-Al2O3-supported system in the selective hydrogenation reactions of p- and o-chloronitrobenzene to the corresponding haloanilines, in mild reaction conditions (25°C, 0.1MPa hydrogen pressure) (p-chloronitrobenzene: specific activity (SA)=59.5min−1, Selectivity (Sel.)=99.9%; o-chloronitrobenzene: SA=42.8min−1, Sel.=99.2%). The Pt/γ-Fe2O3 system also showed high catalytic efficiency (Sel.>98%, at 100% of conversion) in the selective hydrogenations of m-chloro-, p- and o-bromo- and p- and o-iodonitrobenzenes. XPS structural studies performed on a pristine Pt/γ-Fe2O3 sample as well as on a sample recovered after the reaction, indicate that the catalytic process did not induce permanent modification in the chemical and/or electronic structure of the catalyst according with the high reusability of the system. [Copyright &y& Elsevier]

Abstract: Functionalised β-lactones were prepared starting from propargyl alcohols by means of an efficient rhodium-catalysed silylcarbocyclisation reaction. This process took place in high yields and complete stereoselectivity using DBU as the base, a sterically hindered alcohol and/or hydrosilane. Otherwise, a silylformylation competitive reaction occurred affording 3-hydroxy-2-[(aryldimethylsilyl)methylene]alkanals with complete regioselectivity. Indeed, while α-(aryldimethylsilylmethylene)-β-lactones were generated exclusively starting from an alkynol characterised by two alkyl groups on the propargyl carbon atom, significant amounts of the aldehydes were observed for secondary alcohols. In these cases, the use of ortho-substituted arylsilanes improved the chemoselectivity towards the α-methylene-β-lactones. Such molecules were then successfully converted into α-methylaryl-β-lactones by a fluoride-induced rearrangement of the aryl group that migrates from silicon to carbon with retention of configuration. [Copyright &y& Elsevier]

Nitrogen-containing heterocycles are important scaffolds for a large number of compounds with biological, pharmaceutical, industrial and optoelectronic applications. A wide range of different methodologies for the preparation of N-heterocycles are based on metal-catalyzed cyclization of suitable substrates. Due to the growing interest in Green Chemistry criteria over the past two decades, the use of supported metal catalysts in the preparation of N-heterocycles has become a central topic in Organic Chemistry. Here we will give a critical overview of all the solid supported metal catalysts applied in the synthesis of N-heterocycles, following a systematic approach as a function of the type of support: (i) metal catalysts supported on inorganic matrices; (ii) metal catalysts supported on organic matrices; (iii) metal catalysts supported on hybrid inorganic-organic matrices. In particular, we will try to emphasize the effective heterogeneity and recyclability of the described metal catalysts, specifying which studies were carried out in order to evaluate these aspects. [ABSTRACT FROM AUTHOR]

A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described, together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of β-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromofunctionalized substrates undergo an intramolecular reaction that affords exclusively carbacyclobenzyl aldehydes, further enhancing the high synthetic value of this method. [ABSTRACT FROM AUTHOR]

Supported catalysts are important tools for developing green-economy-based processes. Palladium nanoparticles (NPs) that are immobilized on two fibers developed as metal scavengers (i.e., Smopex®-234 and Smopex®-111, 1% w/w) have been prepared and tested in copper-free cyclocarbonylative Sonogashira reactions. Their catalytic activity has been compared with that of a homogeneous catalyst (i.e., PdCl2(PPh3)2). Pd/Smopex®-234 showed high activity and selectivity in the synthesis of functionalized heterocycles, such as phthalans and isochromans, even when working with a very low amount of palladium (0.2–0.5 mol%). The extension of Pd/Smopex®-234 promoted cyclocarbonylative reactions to propargyl and homopropargyl amides afforded the corresponding isoindoline and dihydrobenzazepine derivatives. A preliminary test on Pd NPs leaching into the solution (1.7 × 10−3 mg) seems to indicate that, at the end of the reaction, almost all of the active metal is present on the fiber surface. [ABSTRACT FROM AUTHOR]

We report here the use of eucalyptol as a bio-based solvent for Hiyama coupling, cyanation, and multicomponent reactions on O,S,N-heterocycles. These heterocycles were chosen as targets or as starting materials given their biological potential; they play an important role in therapeutically active compounds. Once again, eucalyptol proved to be a credible and sustainable alternative to common solvents. [ABSTRACT FROM AUTHOR]

Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported. [ABSTRACT FROM AUTHOR]

The acyl Sonogashira reaction represents an extension of Sonogashira cross-coupling to acid chlorides which replace aryl or vinyl halides, while terminal acetylenes are used as coupling partners in both reactions. The introduction of a carbonyl functional group on the alkyne backbone determines a radical change in the reactivity of the products. Indeed, α,β-alkynyl ketones can be easily converted into different heterocyclic compounds depending on the experimental conditions employed. Due to its potential, the acyl Sonogashira reaction has been deeply studied with particular attention to the nature of the catalysts and to the structures of both coupling compounds. Considering these two aspects, in this review, a detailed analysis of the literature data regarding the acyl Sonogashira reaction and its role in the synthesis of several heterocyclic derivatives is reported. [ABSTRACT FROM AUTHOR]

An abstract of the article "Cyclocarbonylative Sonogashira Reactions of 1-Ethynylbenzyl Alcohols: Synthesis of 1-Carbonylmethylene-1,3-dihydroisobenzofurans" by Laura Antonella Aronica and colleagues is presented.

The advantages of the title synthesis are high yield, complete stereoselectivity, low catalyst loading (0.2-0.5 mol%), and no need for CuI as co-catalyst. [ABSTRACT FROM AUTHOR]

We describe here the synthesis of ultrasmall Pt nanoparticles (NPs) obtained by a robust and reliable protocol using UV-Vis photoreduction of a platinum salt precursor, under continuous flow conditions. These ligand-free Pt NPs were rapidly dispersed onto a solid support or stabilized towards aggregation as a colloidal solution by the addition of an appropriate ligand in the reaction mixture. The proposed protocol exploits a microfluidic platform where the Pt 4+ precursor is photo-reduced to small Pt 0 NPs (1.3 nm) at room temperature in the presence of ethanol, without any additional reducing agent. We apply the protocol to prepare Pt NPs highly dispersed on carbon support (Pt/C) proven to be a very efficient heterogeneous catalyst for both the hydrosilylation of terminal alkynes and hydrogenation of nitroaromatic compounds, selected as model reactions. Furthermore, we exploit the versatility of this microfluidic approach to produce stabilized aqueous/ethanol colloidal solutions of Pt NPs, employing a ligand of choice ( e.g. , PVP or a thiol-ligand). These colloids offer long-term storage and further ligand modification. We showcase the synthesis of biocompatible glycol-stabilized Pt nanoparticles as an exemplary application.