The effect of tethered bi-naphthyls on visible-light promoted alkene-alkene [2 + 2] cycloadditions.

Dispersion interactions are ubiquitous weak interactions that can play a role in many chemical events. Tailor-made catalysts and additives can lead to more selective reactions by properly exploiting dispersion interactions. Although radical-π dispersion interactions are known to have an important stabilizing role, this concept has been so far overlooked in synthetic photochemistry.

Valorisation of the Invasive Macroalgae (Harvey) Suringar for the Green Synthesis of Gold and Silver Nanoparticles with Antimicrobial and Antioxidant Potential.

Bacterial and fungal infections are a challenging global problem due to the reported increasing resistance of pathogenic microorganisms to conventional antimicrobials. Nanomaterials are a promising strategy to fight infections caused by multidrug-resistant microbes. In this work, gold (Au@UP) and silver (Ag@UP) nanoparticles were produced for the first time by green synthesis using an aqueous extract of the invasive macroalgae (UP).

Sequential Strategies to Trigger Mild Dearomative Diels-Alder Cyclizations.

Dihydronaphthalenes are present in several functional molecules, but their assembly is challenging. However, a sequential strategy can induce the key annullation of an alkyne with a vinylarene under mild conditions. Products form in good yields, with ample functional tolerance via domino nucleophilic substitution and dearomative Diels-Alder and ene reactions.

Evolution of Triangular All-Metal Aromatic Complexes from Bonding Quandaries to Powerful Catalytic Platforms.

This manuscript describes an overview on the literature detailing the observation of trinuclear complexes that present delocalized metal-metal bonds similar to those of regular aromatics, which are formed combining main group elements. A particular emphasis is given to the structural and electronic features of aromatic clusters that are sufficiently stable to allow their isolation. In parallel to the description of their key bonding properties, the work presents reported catalytic applications of these complexes, which already span from elaborated C-C-forming cascades to highly efficient cross-coupling methods.

Visible-Light Promoted Intramolecular para-Cycloadditions on Simple Aromatics.

Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitization of allenamides.

Gold Nanoparticles Synthesized by an Aqueous Extract of as Potential Antitumoral Enhancers of Gemcitabine.

Cancer still poses a global threat, since a lot of tumors remain untreatable despite all the available chemotherapeutic drugs, whose side effects, it must also be noted, still raise concerns. The antitumoral properties of marine seaweeds make them a potential source of new, less toxic, and more active antitumoral agents. Furthermore, these natural extracts can be combined with nanotechnology to increase their efficacy and improve targeting.

Immunomodulatory and Antitumoral Activity of Gold Nanoparticles Synthesized by Red Algae Aqueous Extracts.

This study reports on the green and cost-efficient synthesis of gold nanoparticles from three different red algae extracts. The nanoparticles synthesized were fully characterized by UV-Vis spectroscopy, HRTEM, and Z-potential. Relevant components occurring in the extracts, such as polysaccharides or phenolic content, were assessed by analytical techniques such as spectrophotometric assays and liquid chromatography.

Synthetic recovery of impulse propagation in myocardial infarction via silicon carbide semiconductive nanowires.

Myocardial infarction causes 7.3 million deaths worldwide, mostly for fibrillation that electrically originates from the damaged areas of the left ventricle. Conventional cardiac bypass graft and percutaneous coronary interventions allow reperfusion of the downstream tissue but do not counteract the bioelectrical alteration originated from the infarct area.

Is Aromaticity a Driving Force in Catalytic Cycles? A Case from the Cycloisomerization of Enynes Catalyzed by All-Metal Aromatic Pd Clusters and Carboxylic Acids.

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.

Ambient Synthesis of Tricyclic Naphthalenes via Stepwise Styryl-yne Dearomative Diels-Alder Cyclization.

A cascade of styrylynols promoted by MnO 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.

Enhancement of X-ray-Excited Red Luminescence of Chromium-Doped Zinc Gallate via Ultrasmall Silicon Carbide Nanocrystals.

X-ray-activated near-infrared luminescent nanoparticles are considered as new alternative optical probes due to being free of autofluorescence, while both their excitation and emission possess a high penetration efficacy . Herein, we report silicon carbide quantum dot sensitization of trivalent chromium-doped zinc gallate nanoparticles with enhanced near-infrared emission upon X-ray and UV-vis light excitation. We have found that a ZnGaO shell is formed around the SiC nanoparticles during seeded hydrothermal growth, and SiC increases the emission efficiency up to 1 order of magnitude due to band alignment that channels the excited electrons to the chromium ion.

Visible-Light-Promoted Polycyclizations of Dienynes.

A variety of linear dienynes can deliver complex tetracyclic frameworks in the presence of an Ir complex and visible light. Product formation involves the generation of four new C-C bonds and six contiguous stereocenters, which decorate two [3.1.

Macroalgae to nanoparticles: Study of Ulva lactuca L. role in biosynthesis of gold and silver nanoparticles and of their cytotoxicity on colon cancer cell lines.

Marine bio-resources are being widely studied as an invaluable source of compounds with therapeutic applicability. In particular, macroalgae contain an extended variety of bioactive compounds with different structures and promising biological applications. In this work, Ulva lactuca L.

Bi-directional alkyne tandem isomerization via Pd(0)/carboxylic acid joint catalysis: expedient access to 1,3-dienes.

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.

Synthesis of Carbolines via Palladium/Carboxylic Acid Joint Catalysis.

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.

Silica-supported sulfonic acids as recyclable catalyst for esterification of levulinic acid with stoichiometric amounts of alcohols.

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.

Boosting catalyst activity in cis-selective semi-reduction of internal alkynes by tailoring the assembly of all-metal aromatic tri-palladium complexes.

Highly symmetric [Pd] 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 Simple Synthesis of Triangular All-Metal Aromatics Allowing Access to Isolobal All-Metal Heteroaromatics.

A simple synthetic method allows the one-pot assembly of C3 -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 rationale of the Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide: unprecedented evidence for a radical mechanism controlling reactivity.

We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred.

Alpha-fluorotropinone immobilized on silica: a new stereoselective heterogeneous catalyst for epoxidation of alkenes with oxone.

The dioxirane-mediated epoxidation of alkenes in the presence of supported alpha-fluorotropinones 5 and 9 has been evaluated. The catalysts anchored onto silica supports 5 have shown comparable activity with respect to the homogeneous counterpart 10 and good stability on recycling. In the second part of this paper the enantiomerically enriched alpha-fluorotropinone 4 was anchored onto both mesoporous MCM-41 and amorphous KG-60 silicas.

Heterogeneous enantioselective epoxidation of olefins catalysed by unsymmetrical (salen)Mn(III) complexes supported on amorphous or MCM-41 silica through a new triazine-based linker.

High enantioselectivity (ee up to 84%) has been achieved in heterogeneous asymmetric epoxidation using a silica-bound unsymmetrical (salen)-manganese(III) complex; amorphous silica can be used in the same way as MCM-41, showing a positive effect in the catalyst recycling.