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An efficient, novel photocatalyzed allylic-alkynylation methodology via copper-based cross-dehydrogenative coupling (CDC) is described. Different types of 1,4-enyne compounds were synthesized in one step at room temperature using copper(I) terpyridyl complex as photocatalyst/initiator. This procedure is an improvement and to some extent complementary to previously reported thermal CDC methods. Preliminary investigations on the reaction mechanism are also presented.

Herein we re-evaluate the synthesis of Poly(e-caprolactone) (PCL) by ring-opening polymerization (ROP) using simple dialkylmagnesium compounds as catalysts. This old reaction has been never studied thoroughly before and a consensus on the intervening mechanism is lacking, being an anionic pathway proposed in the classic literature. In our hands, all tested catalysts exhibit high efficiency and complete conversion was achieved within a few hours with high yield and high number-average molecular weight (Mn) in a living fashion. Moreover, kinetic studies revealed that the ROP of e-CL has a first order dependency on monomer (e-CL) as well as catalyst concentration. Furthermore, mechanistic studies of the ROP demonstrated that the reaction follows a coordination-insertion mechanism where the alkyl group initiates the polymerization and is incorporated as one of the terminal groups in the polymer chain.

Herein we report the synthesis of isotactically enriched poly(cyclohexene carbonate) (PCHC) by the bulk alternating copolymerization of meso-cyclohexene oxide and carbon dioxide using dialkylmagnesium compounds as catalyst. These simple achiral catalysts showed good activity for the isoselective copolymerization, with high yield and high carbonate-linkage contents, in a controlled manner under mild conditions and atmospheric CO2 pressure. The triad sequences in the 13C NMR spectra of these polymers were assigned using Bernoullian statistical methods in order to determine the tacticity of the copolymer. Differential scanning calorimetry analysis confirmed the formation of highly isotactic polycarbonate. Furthermore, kinetic studies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry investigations allowed us to shed light on the reaction mechanism of the polymerization process.

Hypervalent iodine (III) five-membered heterocycles have found broad application as atom-transfer reagents for organic synthesis. Among them, 1-Phenyl-1,2-benziodoxol-3-(1H)-one is known as a traditional benzyne precursor, but no further synthetic applications have been reported. Herein, we report the first synthetic application of 1-phenylbenzidoxole to the synthesis of Phthalides using only CuI as catalyst. High selectivity and yield were achieved under mild reaction conditions with good functional group tolerance. During our investigations, the efficiency of different CuI and CuII catalysts under various reaction conditions were studied. The nature of the leaving group, the substituents on the substrate and temperature, play an important role on both yield and selectivity. Moreover, a plausible mechanistic pathway for this transformation was proposed based on our observations and previous literature reports.

An efficient and green synthetic method for the preparation of N,N-disubstituted tetramethylpyrazinium radical cations was developed, which does not require any solvent or strong alkylating agents. The investigation by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy proved the stability of the prepared radical cation. Moreover, it was shown for the first time that the prepared N,N-disubstituted tetramethylpyrazine can act as a powerful metal-free catalyst for the selective oxidative homocoupling of amines to the corresponding imines under solvent-free conditions. Furthermore, oxygen or even air can be employed as an efficient oxidative reagent.

This Focus Review describes state-of-the-art methods for the preparation of antimicrobial silicones. Given the diversity of antimicrobial activity and their mechanisms, the performance of these materials is highly dependent on the characteristics of the polymeric matrix. Therefore, different synthetic routes have been developed, such as 1) physical treatments, 2) chemical transformations, and 3) copolymerization. This classification is not exclusive, so some products belong to more than one class. Herein, we attempt to present a handy overview of the development of antimicrobial silicones, their most important application fields, the most relevant antimicrobial assays, and, as the title suggests, an overview of the most relevant preparation methods.

5-Hydroxymethylfurfural (HMF) has become a benchmark chemical as it can be obtained by the processing of renewable biomass, making its downstream modification an important topic both in industry an...

Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.

C-H bond functionalization is a well-developed concept that has been thoroughly studied and gives entry to rather complex molecules without the need for previous derivatization of the substrates. The use of copper complexes in allylic C-H bond functionalization under oxidative conditions as an alternative to the well-established palladium-based methodologies remains largely underdeveloped. Here, we show for the first time a selective cross-dehydrogenative coupling reaction between underivatized allylic substrates and terminal alkynes to produce 1,4-enynes in high yields in a single step, using an in situ synthesized copper catalyst and an oxidant.

Silicones and silicone rubbers are omnipresent in household and industrial products such as lubricants, coatings, sealants, insulators, medical devices, etc. This plethora of applications arises from their unparalleled properties including hydrophobicity, low surface energy, chemical inertness, extreme temperature stability, elasticity, and biocompatibility. Even though silicones have been known for more than five decades, their chemistry is still far from fully understood. Industrially, the vast majority of processes for their synthesis, transformation, and use are based on rather well established, alas outdated technologies, which are frequently empirical and poorly investigated. This review attempts to summarize the different approaches for the synthesis of silicone rubbers by vulcanization or curing of silicone polymers, the catalysts used, and the corresponding reaction mechanisms. Apart from the well-known methods (radical, hydrosilylation, and metal-based condensation), novel approaches such as organo- and bio-catalysis are also addressed.

Investigations on synthesis of cyanopropyl-functionalized poly(dimethyl-co-methylhydro)siloxane were done to determine the correlation between conversion of SiH groups and further parameters such as nature of reactants, catalyst, stoichiometry and reaction temperature. A study on the kinetics of hydrosilylation with various siloxane starting materials and allyl cyanide were carried out between 60 and 80 °C showing that the overall reaction with polymeric siloxanes was of the second-order. Converselly, small cyclosiloxanes show first reaction order dependence. Furthermore, a two-phase kinetic behavior on the hydrosilylation reaction was observed, most likely due to catalysts deactivation.

Methyltrioxorhenium acts as a catalyst (5 10 Mol ) for the direct electrophilic trifluoromethylation of various aromatic and heteroaromatic compounds using the hypervalent iodine reagent 1 (trifluoromethyl) 12 benziodoxol 3(1H) one (1). The products are formed in up to 77 yield. Mixtures of regioisomers are obtained in the case of substituted and heteroaromatic substrates. The reaction typically carried out in chloroform solvent at 70 degrees C shows a significant induction period. Monitoring by EPR shows the involvement of radical species. A small kinetic deuterium isotope effect of 1.3 is observed for benzene.

We have prepared a series of new rhenium complexes containing chiral ferrocenyldiphosphane ligands of the Josiphos family, starting from commercially available rhenium sources. These new ReV oxido and nitrido complexes, several of which have been characterized by X-ray crystallography, are air- and moisture-stable and are active catalysts in the asymmetric transfer hydrogenation of ketones using 2-propanol as the hydrogen source in the presence of substoichiometric amounts of triethylamine (TEA). The reaction proceeds cleanly with good to excellent yields (50–99 %) but with moderate enantioselectivity (up to 58 % ee). A mechanism not involving hydridic species is proposed.

New polynuclear zinc complexes containing tridentate Schiff base ligands were successfully synthesized and fully characterized. The solid-state structure of the complexes was determined using single crystal X-ray diffraction. The complexes display a tetranuclear cubane-like core structure [Zn4O4] and sowed good catalytic activity towards the ring-opening polymerization (ROP) of rac-lactide (rac-LA) and ɛ-caprolactone (ɛ-CL) under solvent-free conditions. The polylactic acid (PLA) obtained from rac-LA showed isotactic enrichment, as proved by homonuclear decoupled 1H NMR analysis. These complexes also showed good activity and superior control towards the ROP of rac-LA and ɛ-CL in the presence of benzyl alcohol as a co-initiator. Furthermore, Kinetic studies demonstrated that the ROP of rac-LA and ɛ-CL has a first order dependence on both monomer (rac-LA and ɛ-CL) and catalyst concentration. This article is protected by copyright. All rights reserved.