Unprecedented Nucleophilic Attack of Piperidine on the Electron Acceptor during the Synthesis of Push‐Pull Dyes by a Knoevenagel Reaction

An unprecedented nucleophilic addition of piperidine on an electron acceptor, namely, 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1‐ylidene)malononitrile is reported. This unexpected behavior was observed during the synthesis of push‐pull dyes using the classical Knoevenagel reaction. To overcome this drawback, use of diisopropylethylamine (DIPEA) enabled to produce the expected dyes PP1 and PP2 . The optical and electrochemical properties of the different dyes were examined. Theoretical calculations were also carried out to support the experimental results. To evidence the higher electron‐withdrawing ability of this electron acceptor, a comparison was established with two dyes ( PP3 and PP4 ) comprising its shorter analogue.     

A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation

Direct selective oxidation of hydrocarbons to oxygenates by O₂ is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C?H bonds at benzylic positions. In this work, stable, lead‐free, Cs₃Bi₂Br₉ halide perovskites are integrated within the pore channels of mesoporous SBA‐15 silica and demonstrate their photocatalytic potentials for C?H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C₅ to C₁₆ including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol g_cat^?1 h^?1 and excellent selectivity (>99 %) towards aldehydes and ketones under visible‐light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well‐dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp³)?H bond activation by photoinduced charges.     

Helical γ-Peptide Foldamers as Dual Inhibitors of Amyloid-β Peptide and Islet Amyloid Polypeptide Oligomerization and Fibrillization

Type 2 diabetes (T2D) and Alzheimer's disease (AD) belong to the 10 deadliest diseases and are sorely lacking in effective treatments. Both pathologies are part of the degenerative disorders named amyloidoses, which involve the misfolding and the aggregation of amyloid peptides, hIAPP for T2D and Aβ_1-42 for AD. While hIAPP and Aβ_1-42 inhibitors have been essentially designed to target β-sheet-rich structures composing the toxic amyloid oligomers and fibrils of these peptides, the strategy aiming at trapping the non-toxic monomers in their helical native conformation has been rarely explored. We report herein the first example of helical foldamers as dual inhibitors of hIAPP and Aβ_1-42 aggregation and able to preserve the monomeric species of both amyloid peptides. A foldamer composed of 4-amino(methyl)-1,3-thiazole-5-carboxylic acid (ATC) units, adopting a 9-helix structure reminiscent of 3₁₀ helix, was remarkable as demonstrated by biophysical assays combining thioflavin-T fluorescence, transmission electronic microscopy, capillary electrophoresis and mass spectrometry.     

Carbo‐Quinoids: Stability and Reversible Redox‐Proaromatic Character towards Carbo‐Benzenes

The carbo‐mer of the para‐quinodimethane core is stable within in a bis(9‐fluorenylidene) derivative. Oxidation of this carbo‐quinoid with MnO₂ in the presence of SnCl₂ and ethanol affords the corresponding p‐bis(9‐ethoxy‐fluoren‐9‐yl)‐carbo‐benzene. The latter can be in turn converted back into the carbo‐quinoid by reduction with SnCl₂, thus evidencing a chemical reversibility of the interconversion between a pro‐aromatic carbo‐quinoid and an aromatic carbo‐benzene, and is reminiscent of the behavior of the benzoquinone/hydroquinone redox couple (in the red–ox opposite sense).     

On-Surface Synthesis of Unsaturated Hydrocarbon Chains through C−S Activation

We use an on-surface synthesis approach to drive the homocoupling reaction of a simple dithiophenyl-functionalized precursor on Cu(111). The C−S activation reaction is initiated at low annealing temperature and yields unsaturated hydrocarbon chains interconnected in a fully conjugated reticulated network. High-resolution atomic force microscopy imaging reveals the opening of the thiophenyl rings and the presence of trans- and cis-oligoacetylene chains as well as pentalene units. The chemical transformations were studied by C 1s and S 2p core level photoemission spectroscopy and supported by theoretical calculations. At higher annealing temperature, additional cyclization reactions take place, leading to the formation of small graphene flakes.     

Photocatalyzed Synthesis of 3-Substituted Phthalides: A Key Access to (±)-Herbaric Acid

An efficient organophotocatalyzed protocol was developed for the preparation of 3-substituted phthalides. The presented transformation was performed under particularly mild conditions within 6 h and was ultimately applied to a precursor of the herbaric acid.     

Studies on The Application of The Paternò-Büchi Reaction to The Synthesis of Novel Fluorinated Scaffolds

In the context of new scaffolds obtained by photochemical reactions, Paternò-Büchi reactions between heteroaromatic, trifluoromethylphenyl ketone and electron rich alkenes to give oxetanes are described. A comprehensive study has then been carried out on the reaction of aromatic ketones with fluorinated alkenes. Depending on the substitution pattern at the oxetane ring, a metathesis reaction is described as a minor side process to give mono fluorinated alkenes. Overall, this last reaction corresponds to a photo-Wittig reaction and yield amid isosteres. In order to explain the uncommon regioselectivity of the Paternò-Büchi reaction with these alkenes, electrostatic-potential derived charges (ESP) have been determined. In a second computational study, the relative stabilities of the typical 1,4-diradical intermediates of the Paternò-Büchi reaction have been determined. The results well explain the regioselectivity. Further transformations of the oxetanes or previous functionalization of the fluoroalkenes open perspectives for oxetanes as core structures for biologically active compounds.     

Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible‐Light Applications

Various photosensitizers were grafted by conventional peptide coupling methods to functionalized silica with several macroscopic shapes (powders, films) or embedded in highly transparent and microporous silica xerogel monoliths. Owing to the transparency and free‐standing shape of the monoliths, the transient species arising from irradiation of the PSs could be analyzed and were not strikingly different from those observed in solutions. The observed reactivity for either liquid–solid (α‐terpinene oxygenation vs dehydrogenation) or gas–solid (dimethylsulfide, DMS, solvent‐free oxidation) reactions was consistent with the properties of the excited states of the PSs under consideration. Immobilized anthraquinone‐derived materials preferentially react in both cases by electron transfer from the substrate to the triplet state of the sensitizer, in spite of an efficient singlet oxygen production. The recently developed 9,14‐dicyanobenzo[b]triphenylene‐3‐carboxylic acid, DBTP‐COOH, efficiently reacts via energy transfer to yield singlet oxygen from its triplet state. It was shown to perform better than 9,10‐dicyanoanthracene and rose bengal for DMS oxidation and α‐terpinene photooxygenation to ascaridole, respectively. Thus, by a proper choice of the organic immobilized photocatalyst, it is possible to develop efficient and reusable materials, activated under visible light, for various applications and to tune the reaction pathway, opening the way to green oxidation processes.