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The work details a mechanistic study based on density functional theory modeling on the cycloisomerization of polyunsaturated substrates catalyzed by all-metal aromatic tripalladium complexes and carboxylic acids. These clusters are an emerging class of catalysts for a variety of relevant transformations, including C-C forming processes that occur under mild conditions and display synthetic features complementary to those of established mononuclear complexes. This study is the first computational one devoted to the comprehension of the series of elementary steps involved in a synthetic transformation catalyzed by an all-metal aromatic complex. Present results confirm previous experimental hints on the striking mechanistic differences exerted by these clusters with respect to the usual cyclization pathways of related substrates. Moreover, the catalytic cycle involving present all-metal aromatic clusters closely parallels the mechanism of the aromatic substitution of regular arenes.

DME has been received the attention as a renewable energy due to its thermal efficiencies equivalent to diesel fuel, lower NOx emission, near-zero smoke and non-toxic. DME can be obtained by methanol dehydration over solid acid catalysts or directly from syngas over bifunctional catalysts. The catalytic dehydration of methanol to DME has been widely studied in the literature over pure or modified γ -aluminas (γ-Al2O3) and zeolites. Mesoporous silica has obtained much consideration due to its well-defined structural order, high surface area, and tunable pore diameter. In this work, sulfonic acid and aluminium modified mesoporous silica were synthesized and tested as catalysts for production of dimethyl ether from methanol. The modified silicas were studied utilizing XRD, N2 physisorption, pyridine adsorption, and scanning electronic microscopy. The effects of reaction temperature and water deactivation on the methanol selectivity and conversion to dimethyl ether were investigated. Sulfonic acid modified mesoporous silica showed higher selectivity and stability of DME than that of aluminosilicate. The grafting of mesoporous silica with sulfonic groups displayed much more enhanced hydrothermal stability than Al-MCM-41 and γ-Al2O3.

We report herein a simple catalytic method for the extensive labeling of alkenyl C–H bonds through the combination of a palladium(0) complex and a carboxylic acid in the presence of deuterium oxide. The reaction can be applied to a variety of terminal alkenes and the best results are obtained with aryl-substituted examples. This method represents a convenient approach for the preparation of extensively labeled chemicals from the cheapest and safest source of deuterium.

The influence of a catalyst's surface acidity on the catalytic activity and deactivation in the dehydration of methanol to DME was investigated. Different materials including propylsulfonic acid functionalized silica with different Brønsted acidities, silica-alumina, and propyl and phenylsulfonic acid functionalized silica-alumina catalysts were prepared. All the samples were characterized by XRD, TGA, XPS, N2-sorption, ICP-OES and SEM analysis. It was found that the Brønsted and Lewis acidity of the SiO2/Al2O3-PhSO3H catalyst played a critical role in the performance of methanol to DME transformation. The grafting of sulfonic acid groups on silica-alumina enhanced the surface Brønsted acidity and also the reaction activity and selectivity for the dehydration of methanol to DME. In addition, the phenylsulfonic acid functionalized silica-alumina catalyst exhibited the highest activity and stability for the dehydration reaction at relatively low temperatures at which the γ-Al2O3 catalyst, commercial reference, displayed low dehydration activity. The effect of water was also investigated because in the indirect process to produce DME using acidic γ-alumina, it had the most important effect on catalyst deactivation. As a result, water had a positive effect on methanol dehydration over the SiO2/Al2O3-PhSO3H catalyst in contrast to γ-Al2O3 which was rapidly deactivated. Thus, Brønsted and Lewis acid sites with suitable strength may be responsible for the effective conversion of methanol to DME with high stability and selectivity. This journal is

The work details a mechanistic study based on density functional theory modeling on the cycloisomerization of polyunsaturated substrates catalyzed by all-metal aromatic tripalladium complexes and carboxylic acids. These clusters are an emerging class of catalysts for a variety of relevant transformations, including C-C forming processes that occur under mild conditions and display synthetic features complementary to those of established mononuclear complexes. This study is the first computational one devoted to the comprehension of the series of elementary steps involved in a synthetic transformation catalyzed by an all-metal aromatic complex. Present results confirm previous experimental hints on the striking mechanistic differences exerted by these clusters with respect to the usual cyclization pathways of related substrates. Moreover, the catalytic cycle involving present all-metal aromatic clusters closely parallels the mechanism of the aromatic substitution of regular arenes.

A cascade of styrylynols promoted by MnO2 allows the synthesis of fused tricycles with a naphthalene core. The reaction occurs under ambient conditions, offering a practical synthetic tool because of the inexpensive and abundant manganese species. The method affords products through the sequential oxidation of a propargyl alcohol, stepwise Diels-Alder cyclization, and finally rearomatization. According to density functional theory, the usually unfavorable stepwise Diels-Alder mechanism is instead a general tool for eliciting otherwise challenging dearomative annulation.

Highly diastereoselective hydroxyalkylation of phenols with chiral glyoxylates was performed. Hydrolysis or reduction of the esters 3 afforded 2-hydroxymandelic acids 6 and diols 5 in high yields and enantiomeric pure form. Mechanistic evidence of chelation-controlled reaction comes from the crystal structure determination of titanium phenoxide complex 8.

The controlled dispersion of polymeric sulfonic acids on suitable heterogeneous supports paves the way to a new catalytic method for the oxidation of a variety of benzylic methylenes to the corresponding carbonyls by using hydrogen peroxide; narrowly dispersed silica nanoparticles covered by fluorinated sulfonic acids ionomers allow selective oxidation of toluene to benzaldehyde, minimizing undesired side reactions and formation of wastes.

The global issue of contamination and power reserves has given dimethyl ether (DME) considerable attention. It is an encouraging and clean green material for the future resulting from its clean combustion properties. In this paper, a novel MCM-41-propyl-SO3H catalyst was successfully prepared with tethering of the active sulfonic acid groups onto the support via covalent bonds. This material was investigated as catalyst for DME synthesis via methanol dehydration in a fixed bed flow reactor at different experimental settings. TGA, NH3-TPD, SEM, XRD and BET techniques​ were utilized to characterize the synthesized material. MCM-41 sulfonated catalyst showed great thermal stability, high surface area and significant acid loading. The catalytic tests also demonstrated that the maximum methanol conversion was observed at 350 °C and catalyst contact time of 8 s. In addition, the catalyst showed a total selectivity to DME; light hydrocarbons and higher oxygenated compounds were not formed at temperatures above 300° C.

Dimethyl ether (DME) is an environmentally friendly fuel that is being widely considered as an alternative fuel to replace petroleum fuels. DME can be produced by dehydration reaction of methanol by using solid catalysts in catalytic reactions. This study shows the influence of catalyst's surface acidity on the catalytic activity in the dehydration of methanol to DME. In this work, the conversion of methanol to dimethyl ether has been investigated using a continuous flow fixed-bed reactor at temperatures between 60°C and 350°C and 1 bar. Sulfonated catalysts with-SO3H acid function were tested and compared with conventional catalysts as γ-Al2O3. SiO2, MCM-41 and fluoropolymer were used as inorganic and organic supports for sulfonic groups. The experimental results demonstrate a good catalytic activity for the functionalized MCM-41 and the fluoropolymeric material. Effects of H2O on the activity and deactivation of these catalysts were also studied.

An in situ formed palladium hydride catalyst enables the sequential dual isomerization of propargylamide derivatives to 1-amido-1,3-dienes with high chemo- and regioselectivity. The reaction shows ample functional group tolerance, delivering a valuable class of products, including highly deuterated ones, from readily available reagents. The reaction occurs through a complex mechanism studied by DFT modelling.

We report herein that suitably supported perfluorosulfonic acids can catalyze the oxidative dimerization of anilines using hydrogen peroxide as a clean oxidant. The reaction does not require the use of organic solvents and affords desired azobenzenes and water as products, minimizing the formation of wastes. The metal-free solid catalyst shows remarkable activity and selectivity for the reaction, which occurs under very mild conditions and with broad functional group tolerance.

Deep oxidative desulfurization has been carried out, achieving the production of a model fuel with minimal sulphur content (0–15 ppm). This desulfurization process has been developed in continuous flow, using a titanium supported heterogeneous catalyst and exceptionally low hydrogen peroxide concentration (0.77% w/w).

Highly symmetric all-metal aromatic Pd3+ complexes can catalyze the cycloisomerization of terminal 1,6-enynes and internal dienynes under mild conditions. Modification of substrates dictates the mechanism and steers the reaction toward different polycyclic frameworks, enabling the development of complex cascades. The reactivity of Pd(4/3) complexes is complementary to that of mononuclear Pd(0) and Pd(II) ones.

The first organo-catalyzed synthesis of imidazolidin-2-ones and imidazol-2-ones via intramolecular hydroamidation of propargylic ureas is reported. The phosphazene base BEMP turned out to be the most active organo-catalyst compared with guanidine and amidine bases. Excellent chemo- and regioselectivities to five-membered cyclic ureas have been achieved under ambient conditions, with a wide substrate scope and exceptionally short reaction times (down to 1 min). A base-mediated isomerization step to an allenamide intermediate is the most feasible reaction pathway to give imidazol-2-ones, as suggested by DFT studies.

A variety of linear dienynes can deliver complex tetracyclic frameworks in the presence of an IrIII complex and visible light. Product formation involves the generation of four new C-C bonds and six contiguous stereocenters, which decorate two [3.1.0] bicyclic units tethered through their bridging quaternary carbon atoms. The internal alkyne acts as a formal dicarbenoid for the generation of two cyclopropanes in these radical cation cascades. This behavior has not been previously observed for organic reactive intermediates and can be extended to intermolecular reactions and diendiynes.

Sulfonic acids grafted on inorganic support such as SiO2 and MCM41 was used as catalysts for conversion of methanol to dimethyl ether. In this experimental work the catalysts were compared for their catalytic properties in a continuous flow fixed-bed reactor at temperatures between 180 and 320 °C and 1 bar. It was found that all SO3H-functionalized materials in this study were active, selective and stable for DME synthesis. According to the experimental results MCM-41-(CH2)3-SO3H exhibited the best performance, related to its higher surface area and acidity.

Understanding the poisoning and deactivation pathways of metal-organic frameworks (MOFs) is an essential goal to boost their application as robust and efficient catalysts in chemical transformations relevant to industrial processes. Herein, the acetalization reaction of benzaldehyde with methanol was investigated by using [Cu3(BTC)2] (BTC=1,3,5-benzenetricarboxylate) as a catalyst. The reaction was performed under batch and continuous flow conditions, and the conversion of benzaldehyde into 1,1-dimethoxytoluene proceeded efficiently in the presence of a modest amount of water. Nevertheless, a drastic reduction in the catalytic activity was observed after recycling the MOF for repetitive batch experiments and after prolonged continuous flow tests. Pore clogging of the MOF and partial crystal-structure modifications, gathered from XRD and pore analyses, suggested grinding the catalyst prior to application; the ground catalyst showed a considerable enhancement in catalytic performance.

An environmentally friendly protocol for the selective protection of dicarboxylic acids is reported using methanol as a cheap esterifying agent and alumina as a heterogeneous catalyst; the selectivity of the process has been ascribed to a balanced acidity/basicity of the bifunctional alumina catalyst.

A cheap and easily recoverable heterogeneous catalyst could efficiently trigger C–P bond formation by selective addition of phosphites to the carbonyl group of aldehydes and ketones. The reactions afford the desired products in good to excellent yields and do not require the presence of a solvent. Furthermore, nearly stoichiometric amounts of reagents could be used as the hydrotalcite catalyst does not cause the condensation of the carbonyl derivatives, even when aliphatic aldehydes are employed.

The combination of a Pd(0) complex with benzoic acid converts propargylic tryptamines to the corresponding tetrahydro-β-carbolines. The method uses unprotected indoles and affords the desired products with ample functional group tolerance. Detailed modeling studies reveal a close synergy between the organic and metal catalysts, which enables sequential alkyne isomerization, indole C–H activation, and eventual C–C reductive elimination to afford the target heterocycles.

Dihydrodibenzo[b,f]azepines and dibenzo[b,f]azepines can be efficiently synthesized from aryl bromides, o-bromoanilines and norbornene or norbornadiene by means of palladium catalysis. This protocol gives access to dibenzo[b,f]azepine core containing a variety of electron-withdrawing substituents on both aromatic rings and complements the previously reported methodology where electron rich aryl iodides were preferentially used. The presence of KI, even in sub-stoichiometric amount, is crucial for this three-component reaction. The proper addition of iodide anions has a dramatic effect on reaction rate and selectivity. A formal three-step synthesis of the tricyclic antidepressant Clomipramine (Anafranil (R)) is also described.

International audience; A simple synthetic method allows the one-pot assembly of C-3-symmetric, 44-core-valence-electron, triangular Pd or Pt clusters and their heterobimetallic mixed Pd/Pt analogues. These mixed metal complexes are the first examples of stable triangular all-metal heteroaromatics. In contrast to traditional heteroaromatic molecules formed combining main-group elements, they actually retain structural and electronic features of their homonuclear analogues.

A clean and efficient protocol for the synthesis of a wide variety of N-Boc-s-amino ketones 3a-g has been defined using flow approach. The multistep procedure is based on the s-azidation of unsaturated ketones, consecutive reduction of the azido group, and concomitant amino group protection, and furnishes the desired products in good yields and very low E-factors ranging from 3.1 to 5.6. In batch conditions and by water as reaction medium, poorer yields and complicated reaction mixtures are obtained. Adoption of the flow approach, which combines transformations performed in solvent-free conditions and in EtOAc, has been essential in order to avoid side reactions, poisoning of the reduction catalyst, and use of minimal amount of reactants.

A variety of isocoumarins have been synthesized directly from 2-halobenzoates and ketones through a palladium-catalyzed α-arylation step followed by an intramolecular cyclization process. The addition of iodide anions to the reaction mixture increased yields and selectivities especially when 2-bromobenzoates were employed. This phosphine-free one-pot synthesis features a high functional group tolerance and gives access to richly decorated isocoumarins. This general methodology was successful in the total synthesis of Xyridin A, an important natural product with antibacterial and antifungal activity.

International audience; Suitably delocalized metal-metal bonds can stabilize a particular class of discrete trinuclear complexes that are the transition-metal counterparts of carbon-based aromatics. This chemical stability has pivoted the development of an advantageous catalytic method for the semi-reduction of internal alkynes under transfer hydrogenation condition. The reaction does not require any additional solvent and a simple work-up delivers pure products. This combines with broad functional group tolerance, complete cis-selectivity and catalytic charges down to 100 ppm on multi-gram scale.

It has been recently reported that the reaction of α,β-unsaturated carbonyl derivatives with epoxides in the presence of a homogeneous acid catalyst readily delivers the corresponding dioxepines via formal (4 + 3) cycloaddition. We report herein that the same apparent reactivity can be triggered via heterogeneous catalysis. Characterization of products by means of NMR correlation experiments and DFT modeling revealed, however, that products are the acetals of the unsaturated reagent rather than the desired heterocycles.

The easily synthesis of dihydrofuronaphthoquinones and C-alkenylated naphthoquinones has been investigated through the radical oxidative cyclization of 2-hydroxy-1,4-naphthoquinones and thiophene or furan substituted alkenes catalyzed by manganese(III) acetate. The corresponding heteroaryl substituted dihydrofurans and naphthoquinones have been isolated in good yields.

Converting biomass into value-added chemicals holds the key to sustainable long-term carbon resource management. In this context, levulinic acid, which is easily obtained from cellulose, is valuable since it can be transformed into a variety of industrially relevant fine chemicals. Here we present a simple protocol for the selective esterification of levulinic acid using solid acid catalysts. Silica supported sulfonic acid catalysts operate under mild conditions and give good conversion and selectivity with stoichiometric amounts of alcohols. The sulfonic acid groups are tethered to the support using organic tethers. These tethers may help in preventing the deactivation of the active sites in the presence of water.

International audience; Highly symmetric [Pd3]+ clusters that present delocalized metal–metal bonds can catalyse the selective semi-reduction of internal alkynes to cis-alkenes. Studies on factors governing the formation of all-metal aromatics enabled the design of an optimised catalytic system that delivers cis-alkenes with almost complete selectivity on a gram scale with very low catalyst loadings (0.03 mol%).

A cheap and easily recoverable heterogeneous catalyst could efficiently trigger C–P bond formation by selective addition of phosphites to the carbonyl group of aldehydes and ketones. The reactions afford the desired products in good to excellent yields and do not require the presence of a solvent. Furthermore, nearly stoichiometric amounts of reagents could be used as the hydrotalcite catalyst does not cause the condensation of the carbonyl derivatives, even when aliphatic aldehydes are employed.

We report herein a clean multistep flow process that starting from α,β-unsaturated ketones 1 allows the preparation of N-Boc-γ-amino alcohols 3 in high yields. The final products have been isolated in pure form without any additional purification step. The cleanness and environmental efficiency achieved using our protocol are proven by the calculation of green metrics such as E-factors.

Supported sulfonic acids can be employed as efficient catalysts in the dihydroxylation of 1-methylcyclohexene with aqueous hydrogen peroxide, without the use of additional solvents, under mild condition. The reaction was deeply studied in terms of catalyst, H 2 O 2 /1-methylcyclohexene molar ratio, and percentage of aqueous hydrogen peroxide to achieve the best reaction conditions. Experimental results, catalytic efficiency, and spectroscopy data allow to advance some hypothesis on the reaction mechanism, based on the interaction, likely via H-bond, of hydrogen peroxide with the sulfate groups resulting from the deprotonation of supported sulfonic acids.

Novel solid fluorides were prepared to optimize the β-azidation of α,β-unsaturated ketones. The higher loading of these catalysts compared to that of commercially available fluorides has allowed the use of a smaller mass of catalyst helping the mixing of the reaction mixture. Porous polymeric supports have proved to be more efficient in the presence of water as reaction medium. Water has played a crucial role showing a beneficial effect on the reactivity by improving dispersion of the reaction mixture and also by avoiding organic fouling caused by the retention of the reaction mixture within the polymeric matrix. This has facilitated the recovery of the products from the catalyst. The protocol reported has allowed a significant reduction in the organic solvent required for the complete recovery of the pure product whilst leaving the catalyst clean and reusable. E-factors are in the range of 5.9–10.5 and therefore ca. 3 times smaller than previous procedures operating under solvent-free conditions. To further improve the efficiency of our approach we have developed a protocol operating in a continuous-flow manner that has allowed us to achieve an E-factor of 1.7–1.9, with a reduction of ca. 80% of the corresponding batch conditions. The continuous-flow protocol has allowed us to minimize the use of trimethylsilyl azide making the recovery and reuse of water and catalyst 5f very efficient and simple. Finally, a novel reduction system using palladium on alumina (5 mol%) and equimolar amount of formic acid has been used in the presence of 1 equivalent of di-tert-butyl pyrocarbonate to set a multistep protocol operating in continuous-flow conditions for the preparation of two representative N-Boc-β-amino ketones starting from the corresponding enones with E-factors of 3.2 and 2.7, respectively.

Some silica- and polystyrene-supported sulfonic acids, prepared by tethering or sol–gel techniques, were employed as metal-free heterogeneous catalysts in the oxidation of hydroquinones to the corresponding 1,4-benzoquinones, carried out with 30% aqueous hydrogen peroxide. The activity of these catalysts was tested in the model oxidation of methylhydroquinone under batch conditions: high yield and selectivity at room temperature and under environmentally friendly conditions can be achieved in the presence of SiO 2 –(CH 2 ) 3 –SO 3 H. The heterogeneous catalyst, that can be easily recovered by simply filtration, can be used for at least three cycles affording the same good results (∼80% yield, ∼91% selectivity).

Polystyrene-supported chiral 2,2′-methylenebis[(4S)-4-tert-butyl-2-oxazoline] is a promising heterogeneous catalyst for the enantioselective Henry reaction of nitromethane with substituted benzaldehydes. The process is carried out in ethanol as a green solvent, and the corresponding chiral β-nitroalcohols are obtained in 56–95 % yield with 49–88 % ee.

Silica-supported propylsulfonic acid is a very good heterogeneous catalyst for the Baeyer-Villiger oxidation of cyclic ketones to lactones with stoichiometric 30% aqueous hydrogen peroxide in 1,1,1,3,3,3-hexafluoro-2-propanol as solvent.