Accounts of Chemical Research
DOI: 10.1021/acs.accounts.3c00396
Challenges and Breakthroughs in Z‐Enantioselective Olefin Metathesis
Asymmetric Olefin Metathesis (AOM) represents a highly versatile synthetic tool to lead to relevant chiral building blocks with excellent enantiopurity. As the Z-alkene moiety is ubiquitous in a wide range of natural products, the development of catalysts which are able to control both the Z-selectivity and the enantioselectivity of metathesis transformations is in high demands. This review aims to provide a comprehensive overview covering all the breakthroughs accomplished in the field of challenging Z-enantioselective olefin metathesis, which is of interest in the total synthesis of complex molecules.
K2S2O8 Mediated C‐3 Formylation of Imidazopyridines Using Glyoxylic Acid
A metal-free formylation of imidazopyridines with K2S2O8 via direct decarboxylative cross-coupling of glyoxylic acid is described. This reaction features broad substrate scope, good functional group tolerance, and generate products in good yields. The involvement of radicals in the course of the reaction has been demonstrated by radical trapping experiments with 2,2,6,6-tetramethylpiperidine-1-oxyl and 2,6-di-tert-butyl-4-methylphenol (BHT).
Valeric Biofuels from Biomass‐Derived γ‐Valerolactone: A Critical Overview of Production Processes
This review analyzes critically the production of valeric biofuels from γ-valerolactone, a relevant biomass-derived platform molecule. Initially, the main properties of valeric esters as fuels for spark- and compression-ignition engines are summarized. Then, catalytic routes to valeric esters from γ-valerolactone are meticulously analyzed, describing the acid- and metal-catalyzed reactions taking part in the tandem catalysis. Only works focused on the production of the valeric biofuels were considered, excluding the cases where these esters were observed in minor amounts or as byproducts. The role of the appropriate selection of the support, catalytic species, catalyst preparation and experimental conditions on the valeric ester productivity are thoroughly commented. Finally, some concluding remarks and perspectives are given, mentioning the areas where additional efforts must be done in order to turn the dream of a massive and renewable valeric biofuel production into a reality.
Reactivity Studies of Cyclic Alkyl(Amino) Carbene (cAAC)‐Supported Phosphinidenide with AuCl
A neutral octa-nuclear AuI-cluster (2) with molecular formula [(Cy-cAACPAu)4(AuCl)4] [Cy-cAAC =:C(N-2,6-iPr2C6H3)(C6H10)(CMe2)(CH2)] has been isolated, and structurally characterized by single-crystal X-ray diffraction. 2 has been further studied by NMR and ESI-MS. The μ3-P bridged AuI-cluster 2 possesses a C2 axis that passes through the two Au atoms positioned oppositely of the central Au(I)4P4 core, and two carbene-P chromophores. The emission spectrum of 2 exhibited a broad band with λem at 720 nm, and an average lifetime of 3.36 ns when excited at 388 nm in solid state at room temperature. Cyclic voltammetry (CV) studies revealed that 2 can undergo reversible one-electron oxidation at 0.76 V. The electronic transition in 2 has been further studied by computational methods.
The Ring‐Opening Reaction of Benzofuran Involving the Cleavage of C–O Bond
Ring-opening of (di)benzofurans is a significant area of research in organic chemistry, offering versatile and direct synthetic strategies to access valuable functional phenol derivatives. Transition metal catalysis, particularly nickel-catalyzed reactions, has been extensively explored for the selective cleavage of the C–O bond in (di)benzofuran. Metal-free methods, such as acid catalysis and strong base-mediated process, have also emerged as important alternatives. Organometallic reagents, including Grignard and organolithium reagents, play a pivotal role in promoting efficient C–O bond activation. The field of (di)benzofuran ring opening holds great promise for the synthesis of complex molecules with diverse applications in pharmaceuticals, materials science, and fine chemical synthesis. Continued research efforts will pave the way for innovative strategies and broaden the utility of (di)benzofuran derivatives in various fields.
Electrochemical Valorization of Glycerol via Electrocatalytic Reduction into Biofuels: A Review
Electrochemical conversion of underutilized biomass-based glycerol into high-value-added products provides a green approach for biomass and waste valorization. Plus, this approach offers an alternative to biofuel manufacturing procedure, under mild operating conditions, compared to the traditional thermochemical routes. Nevertheless, glycerol has been widely valorized via electrooxidation, with lower-value products generated at the cathode, ignoring the electroreduction. Here we study and establish a review of the efficient glycerol reduction into various products via the electrocatalytic reduction (ECR) process. This review has been built upon the background of glycerol underutilization and theoretical knowledge about the state-of-the-art ECR. The experimental understanding of the processing parameter influences towards electrochemical efficiency, catalytic activity, and product selectivity are comprehensively reviewed, based on the recent glycerol ECR studies. We conclude by outlining present issues and highlighting potential future research avenues for enhanced ECR application.
Disproportionation of H2O2 to Dioxygen on a Nonheme Iron Center. A Computational Study
Density functional theory studies on the reduction of H2O2 on a nonheme iron center is shown to lead to dioxygen products efficiently through the formation of a μ-1,2-peroxo bridged diiron(III)dihydroxo complex from two iron(IV)-oxo(hydroxo) intermediates.
Abstract
Hydrogen peroxide is a versatile reductant that under the right conditions can react to form dioxygen in an electrochemical reaction. This reaction has a low carbon footprint and applications are being sought for batteries. In this work a computational study is presented on a recently reported nonheme iron(II) complex where we study mechanistic pathways leading to dioxygen formation from H2O2. The work shows that upon reduction of the iron(III)-hydroperoxo species it rapidly leads through heterolytic cleavage of the dioxygen bond to form iron(IV)-oxo(hydroxo). The dimerization reaction of two iron(IV)-oxo(hydroxo) complexes then leads to formation of the dioxygen bond rapidly with small barriers. Dissociation of the dimer expels dioxygen in an exothermic reaction. An alternative mechanism through the formation of a μ-1,2-peroxo-μ-1,1-hydroperoxodiiron(II) intermediate was also tested but found to be highly endergonic. These studies highlight the electrochemical feasibilities of nonheme iron(III)-hydroperoxo complexes.
Synthesis, Docking Studies and Evaluation of Chalcones as Anti‐Helicobacter pylori and antitumoral Agents
Abstract
Helicobacter pylori colonizes the gastric epithelium of 50 % of world population and it is the main etiological agent of human chronic gastritis, peptic ulcer, and gastric cancer. In this study, we synthesized and characterized a series of 14 chalcones and evaluated their anti-H. pylori, NO inhibition (in vitro and in silico), and AGS cells cytotoxic effects. Compounds 3b and 3h showed MIC of 8 μg/mL. We observed structure-activity relationships, mainly related to the influence of methoxy substituent at C-2 (3b) and the nitro group at C-4 (3h) in chalcone scaffold. The fourteen chalcones inhibited the NO production in LPS-stimulated macrophages and showed potential for interaction on the active site of the iNOS enzyme. Finally, 3b and 3h showed the highest selectivity to the AGS cell lines. Thus, ours results suggest 3b and 3h as potential candidates for design of new and effective agents against H. pylori and related diseases.
Electrochemical C‐N Coupling on Tri‐metallic Mo‐embedded Graphdiyne towards Efficient Urea Synthesis
This study provides a new two-dimensional C−N coupling catalyst for urea production by loading three Mo-atoms on graphdiyne.
Abstract
Synthesis of urea by electrochemical C−N coupling is a promising alternative to the conventional approaches. A metal-cluster catalyst generally possesses multi-atomic active sites and can achieve co-adsorption and activation of several species. As a two-dimensional porous material, graphdiyne (GDY) is predicated to be a good substrate for loading a metal cluster. In this study, tri-metallic Mo-embedded graphdiyne (Mo3@GDY) stands out for efficient urea synthesis among several TM3@GDY (TM=Mo, Fe, Co, Ni and Cu), based on density functional theory (DFT) computations. The co-adsorption of side-on N2 and end-on CO on Mo3@GDY is benefit to the formation of the urea precursor *NCON with a negative free energy change (−0.66 eV). The final hydrogenation step is the potential-determining step (PDS) with a medium onset potential (-0.71 V). This work extends the application of GDY and first provides a new approach for the electrochemical synthesis of urea by loading tri-metallic atoms on GDY.