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The development of novel pathways for valorizing low-value streams from pulp, forest, and agricultural industries is crucial for realizing a circular bioeconomy and addressing the needs of both platform chemicals and fuels. Utilizing hemicellulose and lignin as biomass-derived feedstocks facilitates the production of sustainable liquid hydrocarbons, with catalytic hydrodeoxygenation being a key process. In the utilization of hemicellulose for the synthesis of liquid hydrocarbons, the approach involves recovering hemicellulosic sugars from wood and transforming them into furfural, which undergoes catalytic hydrodeoxygenation using a noble metal/zeolite tandem catalyst. This results in the production of pentane as the primary product. The process also generates C7–C10 hydrocarbons through bimolecular condensation of oxygenated intermediates alongside the formation of aromatic structures. Another approach involves a three-step transformation of furfural, including furanic ring rearrangement and [2+2] cycloaddition, which produces a C10 oxygenated precursor with a 4-membered ring. Catalytic hydrodeoxygenation of this precursor results in the formation of cyclobutane-containing hydrocarbons for sustainable aviation fuel applications. In the utilization of lignin for the synthesis of liquid hydrocarbons, the approach involves lignin isolation from biomass and its direct catalytic hydrodeoxygenation into valuable platform chemicals and fuels. Guaiacol serves as a lignin model compound, facilitating optimization of the hydrotreatment process and giving insights into the distribution of the products. The hydrodeoxygenation of two different lignins, isolated from biomass by organosolv and soda pulping, yields bio-oils rich in hydrocarbons and suitable for transportation fuel applications.

The development of novel pathways for valorizing low-value streams from pulp, forest, and agricultural industries is crucial for realizing a circular bioeconomy and addressing the needs of both platform chemicals and fuels. Utilizing hemicellulose and lignin as biomass-derived feedstocks facilitates the production of sustainable liquid hydrocarbons, with catalytic hydrodeoxygenation being a key process. In the utilization of hemicellulose for the synthesis of liquid hydrocarbons, the approach involves recovering hemicellulosic sugars from wood and transforming them into furfural, which undergoes catalytic hydrodeoxygenation using a noble metal/zeolite tandem catalyst. This results in the production of pentane as the primary product. The process also generates C7–C10 hydrocarbons through bimolecular condensation of oxygenated intermediates alongside the formation of aromatic structures. Another approach involves a three-step transformation of furfural, including furanic ring rearrangement and [2+2] cycloaddition, which produces a C10 oxygenated precursor with a 4-membered ring. Catalytic hydrodeoxygenation of this precursor results in the formation of cyclobutane-containing hydrocarbons for sustainable aviation fuel applications. In the utilization of lignin for the synthesis of liquid hydrocarbons, the approach involves lignin isolation from biomass and its direct catalytic hydrodeoxygenation into valuable platform chemicals and fuels. Guaiacol serves as a lignin model compound, facilitating optimization of the hydrotreatment process and giving insights into the distribution of the products. The hydrodeoxygenation of two different lignins, isolated from biomass by organosolv and soda pulping, yields bio-oils rich in hydrocarbons and suitable for transportation fuel applications.

The development of novel pathways for valorizing low-value streams from pulp, forest, and agricultural industries is crucial for realizing a circular bioeconomy and addressing the needs of both platform chemicals and fuels. Utilizing hemicellulose and lignin as biomass-derived feedstocks facilitates the production of sustainable liquid hydrocarbons, with catalytic hydrodeoxygenation being a key process. In the utilization of hemicellulose for the synthesis of liquid hydrocarbons, the approach involves recovering hemicellulosic sugars from wood and transforming them into furfural, which undergoes catalytic hydrodeoxygenation using a noble metal/zeolite tandem catalyst. This results in the production of pentane as the primary product. The process also generates C7–C10 hydrocarbons through bimolecular condensation of oxygenated intermediates alongside the formation of aromatic structures. Another approach involves a three-step transformation of furfural, including furanic ring rearrangement and [2+2] cycloaddition, which produces a C10 oxygenated precursor with a 4-membered ring. Catalytic hydrodeoxygenation of this precursor results in the formation of cyclobutane-containing hydrocarbons for sustainable aviation fuel applications. In the utilization of lignin for the synthesis of liquid hydrocarbons, the approach involves lignin isolation from biomass and its direct catalytic hydrodeoxygenation into valuable platform chemicals and fuels. Guaiacol serves as a lignin model compound, facilitating optimization of the hydrotreatment process and giving insights into the distribution of the products. The hydrodeoxygenation of two different lignins, isolated from biomass by organosolv and soda pulping, yields bio-oils rich in hydrocarbons and suitable for transportation fuel applications.

The development of novel pathways for valorizing low-value streams from pulp, forest, and agricultural industries is crucial for realizing a circular bioeconomy and addressing the needs of both platform chemicals and fuels. Utilizing hemicellulose and lignin as biomass-derived feedstocks facilitates the production of sustainable liquid hydrocarbons, with catalytic hydrodeoxygenation being a key process. In the utilization of hemicellulose for the synthesis of liquid hydrocarbons, the approach involves recovering hemicellulosic sugars from wood and transforming them into furfural, which undergoes catalytic hydrodeoxygenation using a noble metal/zeolite tandem catalyst. This results in the production of pentane as the primary product. The process also generates C7–C10 hydrocarbons through bimolecular condensation of oxygenated intermediates alongside the formation of aromatic structures. Another approach involves a three-step transformation of furfural, including furanic ring rearrangement and [2+2] cycloaddition, which produces a C10 oxygenated precursor with a 4-membered ring. Catalytic hydrodeoxygenation of this precursor results in the formation of cyclobutane-containing hydrocarbons for sustainable aviation fuel applications. In the utilization of lignin for the synthesis of liquid hydrocarbons, the approach involves lignin isolation from biomass and its direct catalytic hydrodeoxygenation into valuable platform chemicals and fuels. Guaiacol serves as a lignin model compound, facilitating optimization of the hydrotreatment process and giving insights into the distribution of the products. The hydrodeoxygenation of two different lignins, isolated from biomass by organosolv and soda pulping, yields bio-oils rich in hydrocarbons and suitable for transportation fuel applications.

We report herein intramolecular (3+2) cycloaddition reactions between ynamides as three-atom components and benzyne. In these intramolecular reactions, the two-bond formation is realized by exploiting benzyne precursors that contain a chlorosilyl group as a linking functionality. This method thus highlights the ambivalent character of the intermediate indolium ylide, which exhibits both nucleophilic and electrophilic properties at its C2 atom.

This course examines important transformations of organotransition-metal species with an emphasis on basic mechanisms, structure-reactivity relationships, and applications in organic synthesis.

Low-valent cobalt complexes equipped with phosphorous type of ligands can promote the intramolecular (3+2) cycloaddition of alkylidenecyclopropanes (ACPs) with alkenes and with allenes. Dienes can also be used as partners, but they afford seven-membered cycloadducts. The reactions are fully diastereoselective and, in some cases, we also observed moderate enantioselectivities, especially when using chiral phosphite ligands.

Herein, we describe for the first time the synthesis of the highly porous Hf-tetracarboxylate porphyrin-based metal-organic framework (MOF) (Hf)PCN-224(M) (M = H2, Co2+). (Hf)PCN-224(H2) was easily and efficiently prepared following a simple microwave-assisted procedure with good yields (56–67%; space-time yields: 1100–1270 kg m−3·day−1), high crystallinity and phase purity by using trifluoromethanesulfonic acid and benzoic acid as modulators in less than 30 min. By simply introducing a preliminary step (10 min), 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin linker (TCPP) was quantitatively metalated with Co2+ without additional purification and/or time consuming protection/deprotection steps to further obtain (Hf)PCN-224(Co). (Hf)PCN-224(Co) was then tested as catalyst in CO2 cycloaddition reaction with different epoxides to yield cyclic carbonates, showing the best catalytic performance described to date compared to other PCNs, under mild conditions (1 bar CO2, room temperature, 18–24 h). Twelve epoxides were tested, obtaining from moderate to excellent conversions (35–96%). Moreover, this reaction was gram scaled-up (x50) without significant loss of yield to cyclic carbonates. (Hf)PCN-224(Co) maintained its integrity and crystallinity even after 8 consecutive runs, and poisoning was efficiently reverted by a simple thermal treatment (175 °C, 6 h), fully recovering the initial catalytic activity.

Low-valent cobalt complexes equipped with phosphorous type of ligands can promote the intramolecular (3+2) cycloaddition of alkylidenecyclopropanes (ACPs) with alkenes and with allenes. Dienes can also be used as partners, but they afford seven-membered cycloadducts. The reactions are fully diastereoselective and, in some cases, we also observed moderate enantioselectivities, especially when using chiral phosphite ligands.

The [2+2] cycloaddition – retro-electrocyclization (CA-RE) reaction allows ready synthesis of redox-active donor-acceptor chromophores from an electron-rich alkyne and electron-poor olefins like tetracyanoethylene (TCNE). The detailed mechanism of the reaction has been subject of both computational and experimental studies. While several studies point towards a stepwise mechanism via a zwitterionic intermediate for the first step, the cycloaddition, the reaction follows neither simple second-order nor first-order kinetics. Recent studies have shown that the kinetics can be understood if an autocatalytic step is introduced in the mechanism, in which complex formation with the donor-substituted tetracyanobutadiene (TCBD) product possibly facilitates nucleophilic attack of the alkyne onto TCNE, generating the zwitterionic intermediate of the CA step. This Concept highlights the convenient use of the “click-like” CA-RE reaction to obtain elaborate donor-acceptor chromophores and the recent mechanistic results.

Recent knowledge in chemistry has enabled the material utilization of greenhouse gas (CO2) for the production of organic carbonates using mild reaction conditions. Organic carbonates, especially cyclic carbonates, are applicable as green solvents, electrolytes in batteries, feedstock for fine chemicals and monomers for polycarbonate production. This review summarizes new developments in the ring opening of epoxides with subsequent CO2-based formation of cyclic carbonates. The review highlights recent and major developments for sustainable CO2 conversion from 2000 to the end of 2021 abstracted by Web of Science. The syntheses of epoxides, especially from bio-based raw materials, will be summarized, such as the types of raw material (vegetable oils or their esters) and the reaction conditions. The aim of this review is also to summarize and to compare the types of homogeneous non-metallic catalysts. The three reaction mechanisms for cyclic carbonate formation are presented, namely activation of the epoxide ring, CO2 activation and dual activation., Nejnovější poznatky v chemii umožnily materiálové využití skleníkových plynů jako je CO2 pro výrobu organických karbonátů za mírných reakčních podmínek. Organické karbonáty, zejména cyklické, jsou použitelné jako zelená rozpouštědla, elektrolyty v bateriích, surovina pro jemné chemikálie a monomery pro výrobu polykarbonátů. Tento článek shrnuje nový vývoj v otevírání kruhu epoxidů s následnou tvorbou cyklických karbonátů na bázi CO2. Přehled dále zdůrazňuje nedávný a hlavní vývoj pro udržitelnou konverzi CO2 od roku 2000 do konce roku 2021 dle dostupné literatury na Web of Science. Článek shrnuje syntézy epoxidů zejména z biosurovin, jako jsou druhy např. rostlinné oleje nebo jejich estery) a reakční podmínky. Tato publikace dále porovnává typy homogenních nekovových katalyzátorů.

In this thesis transition metal promoted cycloadditions of trhee-strained carbocycles were carried out. On one hand, the chemistry of alkydlidenecyclopropenes (ACPs) was explored. Despite the abudant number of cycloadditions involving this systems, their enantioselective versions are scarce. In this context, using a low valent cobalt catalyst, a novel enantioselective intramolecular cycloaddition of ACPs and alkynes was succesfully developed. Moreover, mechanistic experiments and computational analysis of the reaction allowed us to stablish an unkonwk mechanism. In addition, the advantages of cobalt was applied in a intramolecular (3+2+2) cycloaddition of ACPs, alkynes and alkenes construction several polycarbocyclic scaffolds. Moreover, the intramolecular cycloaddition of ACPs with alkenes, allenes and dienes catalysed by cobalt was further analysed. The intermolecular cycloaddition of ACPs and trifluoromethyl ketones was also developed. By employing bulky biaryl phosphines as ligands several exo-methylene trifluoromethyl tetrahydrofurans could be synthetize in good yields albeit in low diastereomeric control. Finally, a novel (3+2) cycloaddition of cyclopropenes tethered to alkynes was accomplished. Employing a low valent cobalt catalyst several cyclopentadienes were synthetize with good efficinect. In addition, the syntehtic utility of this trasnformation was proved by the synthesis of several cyclopentadienyl rhodium complexes.

This course examines important transformations of organotransition-metal species with an emphasis on basic mechanisms, structure-reactivity relationships, and applications in organic synthesis.

The [2+2] cycloaddition - retro-electrocyclization (CA-RE) reaction is a "click-like" protocol for facile synthesis of donor-acceptor chromophores from an alkyne and tetracyanoethylene. Herein we shed light on the mechanism of this reaction by detailed kinetics studies using H-1 NMR spectroscopy. By considering several experiments simultaneously, a variety of mechanistic models was evaluated. Surprisingly, a model in which the final 1,1,4,4-tetracyanobuta-1,3-diene product promoted the first step was the only one that described well the experimental data. This autocatalysis model also involved a non-concerted, stepwise formation of the cyclobutene cycloaddition adduct. By proper choice of conditions, we were able to generate the transient cyclobutene in sufficient amount to verify it as an intermediate using C-13 NMR spectroscopy. For its final retro-electrocyclization step, simple first-order kinetics was observed and only minor solvent dependence, which indicates a concerted reaction.

The [2+2] cycloaddition - retro-electrocyclization (CA-RE) reaction is a "click-like" protocol for facile synthesis of donor-acceptor chromophores from an alkyne and tetracyanoethylene. Herein we shed light on the mechanism of this reaction by detailed kinetics studies using H-1 NMR spectroscopy. By considering several experiments simultaneously, a variety of mechanistic models was evaluated. Surprisingly, a model in which the final 1,1,4,4-tetracyanobuta-1,3-diene product promoted the first step was the only one that described well the experimental data. This autocatalysis model also involved a non-concerted, stepwise formation of the cyclobutene cycloaddition adduct. By proper choice of conditions, we were able to generate the transient cyclobutene in sufficient amount to verify it as an intermediate using C-13 NMR spectroscopy. For its final retro-electrocyclization step, simple first-order kinetics was observed and only minor solvent dependence, which indicates a concerted reaction.

The [2+2] cycloaddition – retro-electrocyclization (CA-RE) reaction allows ready synthesis of redox-active donor-acceptor chromophores from an electron-rich alkyne and electron-poor olefins like tetracyanoethylene (TCNE). The detailed mechanism of the reaction has been subject of both computational and experimental studies. While several studies point towards a stepwise mechanism via a zwitterionic intermediate for the first step, the cycloaddition, the reaction follows neither simple second-order nor first-order kinetics. Recent studies have shown that the kinetics can be understood if an autocatalytic step is introduced in the mechanism, in which complex formation with the donor-substituted tetracyanobutadiene (TCBD) product possibly facilitates nucleophilic attack of the alkyne onto TCNE, generating the zwitterionic intermediate of the CA step. This Concept highlights the convenient use of the “click-like” CA-RE reaction to obtain elaborate donor-acceptor chromophores and the recent mechanistic results.

The Pd-catalyzed dipolar cycloaddition represents a significant synthetic strategy for the construction of useful heterocyclic compounds. This study developed the dipolar [4+2] and [6+2] cycloaddition reactions of benzo[d]isothiazole 1,1-dioxides (BDs) leading to the synthesis of BD-fused 1,3-oxazinane and 1,3-oxazocane derivatives, respectively. In particular, the synthesis of BD-fused 1,3-oxazinanes demonstrated regio- and enantioselective characteristics, resulting in products with good yields, enantioselectivity and regioselectivity (if applicable). Furthermore, the [6+2] cycloaddition reaction developed in this work represented the first strategy for the synthesis of medium-sized ring compounds based on BDs. © 2023 SIOC, CAS, Shanghai, & WILEY-VCH GmbH.

Direct laser writing is a technique for printing complex 3D structures with high resolution by irradiating a photoresist in a two-photon process. Improved resolution and dynamic material properties of the printed structures is critical. Herein, advanced photochemical systems were investigated, potentially enabling dual-wavelength direct laser writing. Such systems consisting of organic photoswitches enable the formation of a single product only when irradiated with two wavelengths. A well-known class of photoswitches was investigated for this purpose and its chemistry was carefully explored. Further, photocatalysis combined with a photoswitch was identified as a possible strategy for the two-colour activated photoresist development.

[EN] A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced.

Sulfur vulcanization is the most used method for curing of natural and synthetic rubbers. The crosslinking degree achieved is usually controlled by adding proper quantities of accelerants, activators, co-activators, retardants, and inhibitors, and influences the hardness, elasticity, hysteresis of elastomers and, consequently, the properties and behavior of the materials that incorporate them. Despite the fine tuning pursued over the years, sulfur crosslinking is still difficult to control both in terms of degree and homogeneity of cross-link. Addition of thermally activable bifunctional reagents able to crosslink the polymer matrix through covalent bonds could be a strategy to modulate and control finely the reticulation grade of elastomers. Tetrazoles can form highly reactive nitrilimines by thermal treatment at appropriate temperature, which can react with the vinyl double bonds present in the rubber. In this work a set of bis-tetrazoles were synthesized and those with the right activation temperatures were used for the curing of styrene-butadiene rubber, acting both as single crosslinkers and together with classic sulfur-based ones. The addition of bistetrazoles simplified and made more efficient the compounding process, allowing to prolong the mixing until optimum dispersion and homogeneity were obtained. Moreover, they led to an improvement in the hysteretic properties of the compound and to the reduction of the non-linearity of the dynamic behavior (Payne effect).

Quantum chemical calculations are reported for the thermal dimerizations of 1,3-cyclohexadiene at 1 atm and high pressures up to the GPa range. Computed activation enthalpies of plausible dimerization pathways at 1 atm agree well with the experiment activation energies and the values from previous calculations. High-pressure reaction profiles, computed by the recently developed extreme pressure-polarizable continuum model (XP-PCM), show that the reduction of reaction barrier is more profound in concerted reactions than in stepwise reactions, which is rationalized on the basis of the volume profiles of different mechanisms. A clear shift of the transition state towards the reactant under pressure is revealed for the [6+4]-ene reaction by the calculations. The computed activation volumes by XP-PCM agree excellently with the experimental values, confirming the existence of competing mechanisms in the thermal dimerization of 1,3-cyclohexadiene.

Quantum chemical calculations are reported for the thermal dimerizations of 1,3-cyclohexadiene at 1 atm and high pressures up to the GPa range. Computed activation enthalpies of plausible dimerization pathways at 1 atm agree well with the experiment activation energies and the values from previous calculations. High-pressure reaction profiles, computed by the recently developed extreme pressure-polarizable continuum model (XP-PCM), show that the reduction of reaction barrier is more profound in concerted reactions than in stepwise reactions, which is rationalized on the basis of the volume profiles of different mechanisms. A clear shift of the transition state towards the reactant under pressure is revealed for the [6+4]-ene reaction by the calculations. The computed activation volumes by XP-PCM agree excellently with the experimental values, confirming the existence of competing mechanisms in the thermal dimerization of 1,3-cyclohexadiene.

type:Communication, We report herein an efficient method to synthesize triptycenes by the reaction of benzynes and anthranoxides, which are electron-rich and readily prepared from the corresponding anthrones. Using this method, 1,9-syn-substituted triptycenes were regioselectively obtained employing 3-methoxybenzynes. This method was also applied to synthesize pentiptycenes. A DFT study revealed that the cycloaddition of lithium anthranoxide and benzyne proceeds stepwise.

Herein, we report dual cobalt and photoredox catalysis enabled [2+2+2] cycloaddition of enediynes to produce tricyclic cyclohexadienes bearing a quaternary bridgehead carbon. A variety of enediynes were used, and the corresponding cyclohexadienes were obtained in good to high yields. The use of a chiral ligand, (S)-Segphos, enabled a highly enantioselective reaction allowing access to highly enantio-enriched cyclohexadienes.

Irradiation of 1-acylindole derivatives that possess a vinylcyclopropane moiety at the end of the acyl side chain by a high-pressure mercury lamp through Pyrex glass under sensitization of an aromatic ketone gave the corresponding cyclised products stereoselectively in high yields. The distribution of the products was highly dependent on the substituents on the cyclopropane ring. In the case of a simple cyclopropane, the product was a mixture of ring-expanded cycloheptene-fused indoline and all -cis-fused cyclopropylcyclobutane-fused indoline through [2 + 2] cycloaddition, while cycloheptene-fused indolines were predominantly produced via formal [5 + 2] cyclisation in the case of substituted cyclopropanes. In particular, the product selectivity was substantially high in the case of silylcyclopropane.

Esta tesis doctoral contiene un primer capítulo introductorio en el que se presenta el contexto histórico de la química sintética moderna y se profundiza en los logros obtenidos en el campo de la activacion C-H catalizada por paladio. También se hace hincapié en las cicloadiciones formales basadas en activación C-H catalizadas por paladio. Además, se comenta también la influencia que han tenido los ligandos tipo aminoácido en este tipo de química. En un segundo capítulo, se describe el desarrollo de una nueva cicloadición formal (4+2) de bencilaminas y alquenaminas con alenos, destacando su variante asimétrica basada en desimetrizacion de diarilmetilaminas. El uso de aminoácidos monoprotegidos como ligandos resulta clave para lograr altos rendimientos y enantioselectividades. En un tercer capítulo, se describe el desarrollo de una nueva cicloadición formal (4+2) basada en la activación de carbonos sp3, de mayor dificultad, de o-metilanilinas.Se realizan varios estudios para entender el mecanismo de la reacción. Se expande el alcance de la reacción mediante el desarrollo de una cicloadición formal (5+2), y se estudia de forma preliminar la variante asimétrica de la misma, siguiendo una estrategia de resolución cinética. Finalmente, en un anexo se presentan los resultados preliminares de una nueva reacción de ciclación basada en activacion de carbonos sp3.

The dihydroazulene/vinylheptafulvene (DHA/VHF) couple presents a photo-/thermoswitch that has attracted interest for the development of molecular solar thermal energy storage systems. Here we present the synthesis and optical properties as well as the switching properties of DHA derivatives incorporating alkyne and norbornadiene (NBD) substituents at position C2. The corresponding VHF isomers exhibited remarkably long lifetimes. Thus, the VHF-to-DHA back-reaction half-life for a derivative with a phenylethynyl substituent was 22 days in acetonitrile at room temperature, while the half-life of a VHF reference compound having a phenyl substituent is around 3.5 h under the same conditions. This finding is particularly attractive in the quest for long-term energy storage systems, considering limited enhancement of molecular weight and maintenance of good quantum yield photoisomerization. Moreover, from the thermal back-reaction of an NBD compound, used as a precursor for the DHA-NBD dyad, we estimated the radical-stabilizing influence of a C(Me)=C(CN)2 substituent.

The dihydroazulene/vinylheptafulvene (DHA/VHF) couple presents a photo-/thermoswitch that has attracted interest for the development of molecular solar thermal energy storage systems. Here we present the synthesis and optical properties as well as the switching properties of DHA derivatives incorporating alkyne and norbornadiene (NBD) substituents at position C2. The corresponding VHF isomers exhibited remarkably long lifetimes. Thus, the VHF-to-DHA back-reaction half-life for a derivative with a phenylethynyl substituent was 22 days in acetonitrile at room temperature, while the half-life of a VHF reference compound having a phenyl substituent is around 3.5 h under the same conditions. This finding is particularly attractive in the quest for long-term energy storage systems, considering limited enhancement of molecular weight and maintenance of good quantum yield photoisomerization. Moreover, from the thermal back-reaction of an NBD compound, used as a precursor for the DHA-NBD dyad, we estimated the radical-stabilizing influence of a C(Me)=C(CN)2 substituent.

[EN] A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced.

Sulfur vulcanization is the most used method for curing of natural and synthetic rubbers. The crosslinking degree achieved is usually controlled by adding proper quantities of accelerants, activators, co-activators, retardants, and inhibitors, and influences the hardness, elasticity, hysteresis of elastomers and, consequently, the properties and behavior of the materials that incorporate them. Despite the fine tuning pursued over the years, sulfur crosslinking is still difficult to control both in terms of degree and homogeneity of cross-link. Addition of thermally activable bifunctional reagents able to crosslink the polymer matrix through covalent bonds could be a strategy to modulate and control finely the reticulation grade of elastomers. Tetrazoles can form highly reactive nitrilimines by thermal treatment at appropriate temperature, which can react with the vinyl double bonds present in the rubber. In this work a set of bis-tetrazoles were synthesized and those with the right activation temperatures were used for the curing of styrene-butadiene rubber, acting both as single crosslinkers and together with classic sulfur-based ones. The addition of bistetrazoles simplified and made more efficient the compounding process, allowing to prolong the mixing until optimum dispersion and homogeneity were obtained. Moreover, they led to an improvement in the hysteretic properties of the compound and to the reduction of the non-linearity of the dynamic behavior (Payne effect).

H-bonded counterion-directed catalysis (HCDC) is a strategy wherein a chiral anion that is hydrogen-bonded to the achiral ligand of a metal complex is responsible for enantioinduction. In this article we present the application of H-bonded counterion-directed catalysis to the Au(I)-catalyzed enantioselective tandem cycloisomerization-addition reaction of 2-alkynyl enones. Following the addition of C-, N- or O-centered nucleophiles, bicyclic furans were obtained in moderate to excellent yield and enantioselectivity (28 examples, 59-96 % yield, 62 : 38 to 95 : 5 er). The optimal catalytic system, comprising a phosphinosquaramide Au(I) chloride complex and a BINOL-derived phosphoramidate Ag(I) salt, was selected in a combinatorial fashion from a larger library with the help of high-throughput screening. An enantioselectivity switch of ca. 120 Delta ee% was observed upon addition of the achiral Au(I) component to the Ag(I) salt.

Schinortriterpenoids, such as pre-schisanartanin A and arisanlactone C, are complex and highly oxygenated polycyclic terpenes. In this study, the left-hand fragment of this class terpenes, which possesses oxygen-functionality at C19, was synthesized through [3+2] cycloaddition with excellent diastereoselectivity. This stereoselectivity was investigated by computational studies. Further selective transformation provided a tricyclic skeleton with the desired stereochemistry.

Producción Científica, In this work, the ionic liquid [Aliquat][Cl] was supported into alginate and silica aerogel matrices and applied as a catalyst in the cycloaddition reaction between CO2 and a bio-based epoxide (limonene oxide). The efficiency of the alginate aerogel system is much higher than that of the silica one. The method of wet impregnation was used for the impregnation of the aerogel with [Aliquat][Cl] and a zinc complex. The procedure originated a well-defined thin solvent film on the surface of support materials. Final materials were characterised by Fourier Transform Infrared Spectroscopy, N2 Adsorption–Desorption Analysis, X-ray diffraction, atomic absorption and Field Emission Scanning Microscopy. Several catalytic tests were performed in a high-pressure apparatus at 353.2 K and 4 MPa of CO2.

Covalent surface modification of medical grade PVC tubing was performed using copper-free azide-alkyne cycloaddition reactions to prepare anti-fouling surfaces. PVC azide surface was synthesized by nucleophilic substitution of labile chlorine with sodium azide in the presence of phase transfer catalyst in aqueous media to minimize loss of plasticizer. Electron-poor alkynes with different functionality (zwitterionic, polyethylene oxide, polyfluoro and quaternary amines) were synthesized and covalently attached to the PVC azide surface by thermal azide-alkyne cycloaddition reactions. The reaction progress was monitored by ATR-FTIR spectroscopy. Static contact angle, surface free energy, contact angle hysteresis and atomic force microscopic images were taken for each modified surface. Except for the C6F13 polyfluoro group, the other functional groups containing zwitterionic, polyethylene oxide and quaternary ammonium display hydrophilic properties with the initial SCA in the range of 35-80° due to the strong surface charges. All the modified PVC surfaces maintain their wetting properties against vigorous water rinsing for long period of time (over 60 minutes of sonication) confirming strong covalent bonding of the functional groups to the surface. The antifouling activity of these modified endotracheal tubing samples was evaluated by bacterial adherence assay using Pseudomonas aeruginosa, a gram-negative opportunistic and nosocomial pathogen. Although the adherence assays demonstrate that high polyfluoro (di-ester of C6F13) and long quaternary amine functionality samples slightly reduced P. aeruginosa adherence to endotracheal tubing, the inhibition was not as strong as expected. X-Ray Photoelectron Spectroscopy revealed a pre-existing silicone coating on the original commercial samples, dampening the effects of biofilm inhibition from the chemical modification procedures.

The stereocontrolled formation of medium-sized carbocycles is a major goal in modern organic chemistry due to their widespread occurrence in natural products and pharmaceutically active ingredients. One approach consists in the use of cycloaddition reactions which notably results in high selectivities and atom-economy. To this end, cyclopropanes are ideal substrates since they can provide readily functionalized three- or five-carbon synthons. Herein we report advances made in cycloaddition reactions of cyclopropanes towards the synthesis of medium-sized carbocycles via transition metal catalysis or Lewis acid catalysis.

Covalent surface modification of medical grade PVC tubing was performed using copper-free azide-alkyne cycloaddition reactions to prepare anti-fouling surfaces. PVC azide surface was synthesized by nucleophilic substitution of labile chlorine with sodium azide in the presence of phase transfer catalyst in aqueous media to minimize loss of plasticizer. Electron-poor alkynes with different functionality (zwitterionic, polyethylene oxide, polyfluoro and quaternary amines) were synthesized and covalently attached to the PVC azide surface by thermal azide-alkyne cycloaddition reactions. The reaction progress was monitored by ATR-FTIR spectroscopy. Static contact angle, surface free energy, contact angle hysteresis and atomic force microscopic images were taken for each modified surface. Except for the C6F13 polyfluoro group, the other functional groups containing zwitterionic, polyethylene oxide and quaternary ammonium display hydrophilic properties with the initial SCA in the range of 35-80° due to the strong surface charges. All the modified PVC surfaces maintain their wetting properties against vigorous water rinsing for long period of time (over 60 minutes of sonication) confirming strong covalent bonding of the functional groups to the surface. The antifouling activity of these modified endotracheal tubing samples was evaluated by bacterial adherence assay using Pseudomonas aeruginosa, a gram-negative opportunistic and nosocomial pathogen. Although the adherence assays demonstrate that high polyfluoro (di-ester of C6F13) and long quaternary amine functionality samples slightly reduced P. aeruginosa adherence to endotracheal tubing, the inhibition was not as strong as expected. X-Ray Photoelectron Spectroscopy revealed a pre-existing silicone coating on the original commercial samples, dampening the effects of biofilm inhibition from the chemical modification procedures.

Construction of rings through reliable reactions followed by changes in the ring size or the connectivity through skeletal rearrangement provides molecules with a wide range of skeletons. In this account, our syntheses of polycyclic natural products through skeletal rearrangement are discussed.

Producción Científica, In this work, the ionic liquid [Aliquat][Cl] was supported into alginate and silica aerogel matrices and applied as a catalyst in the cycloaddition reaction between CO2 and a bio-based epoxide (limonene oxide). The efficiency of the alginate aerogel system is much higher than that of the silica one. The method of wet impregnation was used for the impregnation of the aerogel with [Aliquat][Cl] and a zinc complex. The procedure originated a well-defined thin solvent film on the surface of support materials. Final materials were characterised by Fourier Transform Infrared Spectroscopy, N2 Adsorption–Desorption Analysis, X-ray diffraction, atomic absorption and Field Emission Scanning Microscopy. Several catalytic tests were performed in a high-pressure apparatus at 353.2 K and 4 MPa of CO2.

Low‐valent cobalt complexes equipped with chiral ligands can efficiently promote highly enantioselective (3+2) cycloadditions of alkyne‐tethered alkylidenecyclopropanes. The annulation allows to assemble bicyclic systems containing five‐membered rings in good yields and with excellent enantiomeric ratios. We also present a mechanistic discussion based on experimental and computational data, which support the involvement of CoI/CoIII catalytic cycles

The Diels–Alder reaction is one of the most popular reactions in organic chemistry. However, its use in the field of on-surface synthesis is hampered by the spatial restrictions of this cycloaddition reaction. Herein we selected a cyclic strained triyne to demonstrate an on-surface hexadehydro-Diels–Alder reaction in a single molecule. The reaction was studied in detail by means of atomic force microscopy (AFM) with CO-functionalized tips. Our results pave the way to use this iconic pericyclic reaction for on-surface synthesis, introducing the concept of atom economy in the field

Recent progress in the characterization, synthesis, reactivity and application of four-membered ring heterocycles with three heteroatoms with at least one oxygen, sulfur or nitrogen atom are covered in this chapter for the period since 2007. Theoretical and structural methods, including X-ray diffraction analysis, NMR spectroscopy, IR spectroscopy and mass spectrometry, of some representative compounds are first described. Then, their synthesis and reactivity are discussed with an emphasis on the most important transformations reported recently. The last section is devoted to highlight some applications of these four-membered heterocycles which have been used in various domains, such as in catalysis., SCOPUS: ch.b, info:eu-repo/semantics/published

The reaction between epoxides and CO2 to yield cyclic carbonates is efficiently promoted under solvent-free and relatively mild reaction conditions (0.5 mol % catalyst loading, 0.8 MPa, 125 °C) by zinc(II) complexes of pyridine containing macrocyclic ligands (Pc−L pyridinophanes). The zinc complexes have been fully characterized, including X-ray structural determination. The [Zn(II)X(Pc−L)]X complexes showed good solubility in several polar solvents, including cyclic carbonates. The scope of the reaction under solvent-free conditions has been studied and good to quantitative conversions with excellent selectivities have been obtained, starting from terminal epoxides. When solvent-free conditions were not possible (solid epoxides or low solubility of the catalyst in the oxirane) the use of cyclic carbonates as solvents has been successfully investigated. The remarkable stability of the catalytic system has been demonstrated by a series of consecutive runs.

The search for more sustainable solutions for plastics production, moving away from petrochemical feedstocks as today's major raw material basis, is a research area of increasing interest. This task goes far beyond the issue of designing greener polymers and their related monomers as tailor-made plastics require, besides the polymer itself, further components. These additives also need to be switched from typically fossil-based to bio-renewable raw materials. One of such necessary components for many applications are plasticizers, and a major application of them is related to polyvinyl chloride (PVC) as one of the leading polymers with a wide range of applications. Typically today‘s plasticizers are based on fossil feedstocks, and some of them such as specific ortho-phthalates as the most important product class of plasticizers are now subject to restrictions and authorization by the EU's REACH legislation due to their toxicological profile. In this contribution, we report the synthesis and technical evaluation of alternative, novel bicyclic plasticizer candidates, which are fully accessible from renewable feedstocks. In detail, these new plasticizer target molecules are based on the use of the furan-derivative 2-methylfuran, maleic anhydride and 2-ethylhexanol as bio-based starting materials. The synthetic concept consists of an initial Diels-Alder reaction with 2-methylfuran and a subsequent hydrogenation and optional esterification step. The applied reactions are well-known as economic and sustainable technologies. Thus, not only the starting materials (being of bio-based origin) but also the selected reaction technologies for the syntheses of the target molecules are sustainable. Furthermore, a range of performance tests enabled an insight into structure-performance relationships and revealed promising plasticizing properties of this new bio-based plasticizer generation with, e. g., an attractive solution temperature fulfilling the criterium for a “fast fuser” a, Bundesministerium für Bildung und Forschung (BMBF)

Methyl vinyl glycolate (MVG, methyl 2‐hydroxybut‐3‐enoate) is a new biobased platform chemical, which is available by degradation of carbohydrates. In the present work, the oxidation of MVG to methyl 2‐oxobut‐3‐enoate has been investigated and a procedure developed with the Dess‐Martin periodinane. Methyl 2‐oxobut‐3‐enoate has not been characterized before and is stable for days at −18 °C, but slowly dimerizes by an unusual hetero‐Diels‐Alder reaction at room temperature. Therefore, the reactivity of methyl 2‐oxobut‐3‐enoate in the normal Diels‐Alder reaction with 1,3‐dienes has been investigated and a one‐pot procedure developed where MVG is first oxidized with the Dess‐Martin periodinane followed by addition of the 1,3‐diene. A number of different 1,3‐dienes can take part in the cycloaddition to afford the functionalized cyclohexene products in moderate‐to‐good yields.

Low-valent cobalt complexes equipped with chiral ligands can efficiently promote highly enantioselective (3+2) cycloadditions of alkyne-tethered alkylidenecyclopropanes. The annulation allows to assemble bicyclic systems containing five-membered rings in good yields and with excellent enantiomeric ratios. We also present a mechanistic discussion based on experimental and computational data, which support the involvement of Co/Co catalytic cycles.

An efficient and easy protocol for performing 1,3-dipolar cycloaddition using azomethine ylides and acrolein is presented. The reaction catalyzed by d-proline allows the synthesis of C-3 unsubstituted pyrrolidines. The application of this methodology to the synthesis of an advanced intermediate in the preparation of a Hepatitis C virus inhibitor is presented. Final attempts to complete the synthesis of the target inhibitor results in the preparation of its C-4 epimer in good overall yield

Suitably engineered molecular systems exhibiting triplet excited states with very long lifetimes are important for high-end applications in nonlinear optics, photocatalysis, or biomedicine. We report the finding of an ultra-long-lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, measured for a globular tridecafullerene with a highly compact glycodendrimeric structure. A series of three tridecafullerenes bearing different glycodendrons and spacers to the C-60 units have been synthesized and characterized. UV/Vis spectra and DLS experiments confirm their aggregation in water. Steady-state and time-resolved fluorescence experiments suggest a different degree of inner solvation of the multifullerenes depending on their molecular design. Efficient quenching of the triplet states by O-2 but not by waterborne azide anions has been observed. Molecular modelling reveals dissimilar access of the aqueous phase to the internal structure of the tridecafullerenes, differently shielded by the glycodendrimeric shell.

© 2020, Springer Nature B.V. Abstract: Lignocellulosic wastes obtained from vegetal residues in combination with nucleophiles were used as catalysts for carbon dioxide fixation in epoxides to form cyclic carbonates. An adequate combination of the residue and the nucleophile was essential to obtain active catalytic systems. The best binary systems were formed by olive bones, grape waste, date pit and corn leaves husk residues with tetrabutylammonium bromide (TBAB). High conversions in the cycloaddition of CO2 to propylene oxide (76–84%) and 1,2-epoxyhexane (68–79%) were achieved at very low nucleophile loading (0.47 mol % respect to the substrate) under mild conditions (95 °C and 10 atm of CO2). The vegetal wastes were stable under catalytic conditions and could be recycled after adequately supporting the nucleophile TBAB in silica gel. The mechanistic computational study carried out with Density Functional Theory calculations on model catalysts describes the contribution of individual lignin and cellulosic components to the experimental substrate conversion into cyclic carbonate. The energy barriers obtained and the experimental data suggest that the contribution of lignin to the total catalytic activity (barrier energy of 9.9 kcal/mol) may be more important than the contribution of cellulose (energy barrier 11.9 kcal/mol). Graphic abstract: [Figure not available: see fulltext.]

The ability of highly energetic metal-carbene intermediates to engage in complex cascade or formal cycloaddition processes is one of the most powerful tools for building intricate molecular architectures in a straightforward manner. Among this type of organometallic intermediates, non-acceptor metal carbenes are particularly challenging to access and, therefore, have experienced slower development. In this regard, our group has exploited the use of electrophilic gold(I) complexes to selectively activate certain classes of substrates for the generation of this type of intermediate. Thus, very different types of molecules, such as enynes or 7-substituted cycloheptatrienes, lead to the formation of carbenes under gold(I) catalysis. Related rhodium(II) carbenes can also be generated from cycloheptatrienes. In this account, we aim to summarize our efforts towards the in situ generation of such highly versatile organometallic species as well as studies on their reactivity through formal cycloadditions or complex cascade reactions.

We provide a comprehensive DFT investigation of the mechanistic details of CO2 fixation into styrene oxide to form styrene carbonate, catalyzed by potassium iodide-tetraethylene glycol complex. A detailed view on the intermediate steps of the overall reaction clarifies the role of hydroxyl substances as co-catalysts for the alkali halide-catalyzed cycloaddition. The increase of iodide nucleophilicity in presence of tetraethylene glycol is examined and rationalized by NBO and Hirshfeld charge analysis, and bond distances. We explore how different alkali metal salts and glycols affect the catalytic performance. Our results provide important hints on the synthesis of cyclic carbonates from CO2 and epoxides promoted by alkali halides and glycol complexes, allowing the development of more efficient catalysts.