Transfer hydrogenation (TH) offers a sustainable approach for the oxidation of poly-hydroxylated substrates without the need for protecting groups or strong oxidants. Herein, we present a comparative study between the Kn & ouml;lker catalyst (iron) and the Shvo catalyst (ruthenium) for the oxidation of bio-derived polyols. While both catalysts show similar efficiencies in the conversion of model triols, their behaviour diverges significantly with more complex substrates. For sugar-derived polyols, the Kn & ouml;lker complex promotes the selective oxidation of primary alcohols, affording lactones in moderate yields, while the Shvo catalyst leads to extensive epimerisation and complex mixtures. In contrast, the Shvo system proves to be more effective for less reactive substrates, including certain polyols and amidopolyols, with higher conversions. These results highlight the strong influence of substrate structures on catalyst performance and demonstrate the potential of iron-based systems as selective alternatives to noble metal catalysts in sustainable oxidation processes.

A combined experimental and theoretical study on the iron-catalyzed oxidation of unprotected triols incorporating vicinal diols into hydroxylactones is presented using the Knölker catalyst. Focused on triols as mimics for complex polyols derived from sugars, this report rationalizes the difference in reactivity and selectivity observed between vicinal and nonvicinal primary alcohols in transfer hydrogenation. Moreover, DFT calculations performed on a model substrate allowed us to elucidate the key steps of the sequence, highlighting that the final oxidation step determines the selectivity of the whole process. Interestingly, the final product distribution was unexpectedly governed by an entropic contribution instead of electronics or steric effects.

Allylboration reactions of ketones catalyzed by BINOL derivatives can exhibit highly variable stereochemical courses depending on the nature and reactivity of the ketone substrate. In this Article, we put into perspective the relationship between the nature of the starting material and the active species involved in the asymmetric allyboration catalyzed by BINOL derivatives. This work, aimed at comparing different plausible mechanisms by density functional theory (DFT) at the M06-2X/6-311+G(d,p) level involving different types of allylboronates in the presence of the organocatalyst, leads to the confirmation of the hitherto accepted hypothesis of a reaction promoted by the transient cyclic allyl-1,3,2-dioxaborolane derived from BINOLs in the case of unactivated or weakly activated ketones such as indanone. A hypothetical scenario involving dimeric boronate species as chiral catalysts was also investigated.

The synthesis of polycyclic γ- and δ-lactams bearing up to four contiguous fully controlled stereocenters is presented. For that purpose, we developed an original approach based on the use of 2,3-epoxyamides in domino reactions by taking advantage of the nucleophilic nitrogen atom and electrophilic epoxide. In reaction with enol ethers bearing gem bis-electrophiles on the double bond as Michael acceptors, four different reaction pathways were observed. They all started with a domino oxa-Michael/aza-Michael/epoxide opening sequence and depending on substrates engaged could be followed either by a lactonization or a hemiketalization/retro-aldol cascade. Thus, four original fully-substituted piperidine- or pyrrolidine-2-one scaffolds were selectively synthesized in good to high yields. Moreover, these polycyclic lactams were obtained in high stereo- and chemo-selectively highlighting the efficiency and molecular diversity offered by this new methodology that should offer various synthetic opportunities in the future.

Knölker complexes have been recently used to perform the catalytic C1‐oxidation of unprotected sugars into sugar lactones. This oxidation method remained limited by the stability of the catalyst with the polyhydroxylated substrates. Our objective is now to overcome these limitations and extend this method to more challenging substrates such as disaccharides. We proposed in this paper two original designs of Knölker‐type complexes conceived to promote secondary H‐bond interactions with the OH groups of the substrates to stabilise the system and favour the transformation. In total, 8 novel pre‐catalysts were synthesised, fully characterised and applied in the anomeric oxidation of several sugar derivatives. Two of these new complexes proved to be more efficient than the Knölker complex for the oxidation of disaccharides. Moreover, a preliminary DFT study revealed the presence of H‐bonds interactions between the substrate and the oxygen atom on the ligand arm of the best complexes suggesting a beneficial role of this heteroatom on the catalytic efficiency.

Chemical analysis of archaeological sediments is a research area that has long interested archaeologists but has seen recent developments. It locates concentrations of chemical elements in soils that can be linked to ancient activities responsible for their deposition. The use of X-ray fluorescence spectrometry, a more accessible analytical technique than others, makes it possible to analyze large batches of samples. At Ulpiana, two trenches were studied. In the first area, the presence of a lime pit and a mortar preparation area was identified. The signature of the lime seems to correspond to that produced in a kiln discovered further north. In the second area, a bronze recycling workshop was identified, along with a suspected dye molecule.

In this work, five novel A-π-D-π-A type molecules D1-D5 were designed by adding unusual benzothiadiazole derivatives as π-spacer blocks to the efficient reference molecule DRCN5T for application as donor materials in organic solar cells (OSCs). Based on a density functional theory approach, a comprehensive theoretical study was performed with different functionals (B3LYP, B3LYP-GD3, B3LYP-GD3BJ, CAM-B3LYP, M06, M062X, and wB97XD) and with different solvent types (PCM and SMD) at the extended basis set 6-311+g(d,p) to evaluate the structural, optoelectronic, and intramolecular charge transfer properties of these molecules. The B3LYP-GD3BJ hybrid functional was used to optimize the studied molecules in CHCl3 solution with the SMD model solvent as it provided the best results compared to experimental data. Transition density matrix maps were simulated to examine the hole-electron localization and the electronic excitation processes in the excited state, and photovoltaic parameters including open-circuit photovoltage and fill factor were investigated to predict the efficiency of these materials. All the designed materials showed promising optoelectronic and photovoltaic characteristics, and for most of them, a red shift. Out of the proposed molecules, [1,2,5]thiadiazolo[3,4-d]pyridazine was selected as a promising π-spacer block to evaluate its interaction with PC61BM in a composite to understand the charge transfer between the donor and acceptor subparts. Overall, this study showed that adding π-spacer building blocks to the molecular structure is undoubtedly a potential strategy to further enhance the performance of donor materials for OSC applications.

An improvement in the catalytic enantioselective allylboration of isatins with 2-allyl-1,3,2-dioxaborolane in the presence of chiral BINOL derivatives is reported, offering an efficient one-step access to enantioenriched N-unprotected 3-allyl-3-hydroxy-2-oxindoles. This catalytic process is also effective for the crotylboration reaction with enantiomeric ratios (er) up to 97:3, as well as for the asymmetric synthesis of homopropargylic alcohols via an allenyl addition to indoline-2,3-diones. Origins of the high enantioselectivity in chiral BINOL-catalyzed allylboration of isatins were examined by DFT calculations. A hypothetical scenario suggested a crucial internal hydrogen bonding between the amide group (C=O center dot center dot center dot H-O) and the ethylene hydroxyl of the transient chiral mixed boronate ester, generating a rigid and stabilized system that favors the addition of the allylboron species to the Re face of the ketone function. The key role of the alcohol additive (t-BuOH or t-AmOH) in the enantioselective allylboration reaction of isatins has also been shown on the basis of a kinetics study and computational calculations by favoring the transesterification of the 2-allyl-1,3,2-dioxaborolane with BINOL via proton transfer processes.

Saint‐Maurice Abbey in Carnoët (Finistère) underwent an in‐depth archaeological appraisal during 2018–2019, involving several non‐destructive technologies: the geophysical survey revealed the presence of expected structures, drawn on ancient plans, but also the presence of structures unknown up until now. A group of buildings on the edge of the pond in particular raised several questions. A geochemical survey was carried out there in order to try to characterize these buildings and observe the potential complementarity between geophysical and geochemical surveys. The results of the chemical analysis do not highlight the same level of detail of the structures as electrical resistivity, but these analyses seem to be able to clarify the geophysical diagnosis by discriminating signals of structures from echoes linked to the geological substrate.

Enantiopure (R) and (S) cyclic α,α-disubstituted amino acid derivatives displaying a δ-valerolactam side chain were prepared from a common isoxazolidine precursor. The (R)-configured δ-valerolactam 11 was converted into diastereoisomeric pseudopeptides to investigate its ability to induce secondary structures in peptidomimetics. Conformational studies of these pseudopeptides were carried out in the solid state (X-ray diffraction), in solution (NMR analyses), and in silico (computer-aided conformational analysis), which demonstrated that such quaternary amino acids induce β-turn conformations stable enough to be retained in polar media (DMSO). Incorporation of this new type of α,α-disubstituted amino acid into a representative pseudopeptidic sequence by N- then C-elongation and N-debenzylation is also described herein and could serve for the synthesis of various structured peptidomimetics.

Aldol addition of α-triisopropylsilyl-α-diazoacetone (TIPS-diazoacetone), promoted by excess lithium diisopropylamide (LDA), was developed and applied to the synthesis of original C-TIPS diazoaldols, C-TIPS diazoketols, and a related Mannich-type product. An unprecedented mechanistic pathway has been proposed, involving a lithiated triazene intermediate resulting from the nucleophilic addition of LDA on the diazo moiety, supported by experimental results and DFT calculations.

An efficient two‐step strategy for the synthesis of constrained C‐glycosyl amino acid derivatives from C‐vinylglycosides involving a 1,3‐dipolar cycloaddition using l‐(–)‐menthone‐derived nitrone as the key step is described. After optimization of 1,3‐dipolar cycloaddition conditions, various C‐vinylglycosides were tested leading exclusively to one diastereoisomer of the corresponding cycloadduct in good to excellent yields. The total facial selectivity observed was also studied by DFT calculations. Original conformationally restricted C‐glycosyl amino acid derivatives (8 examples) were isolated after simple cleavage of the chiral auxiliary.

Abstract 3,4‐Dihydro‐2H‐pyrans are present in the skeletons of several natural products, and these versatile synthetic intermediates are readily transformed into tetrahydropyrans, pyridines, or 1,5‐dicarbonyl units. Among the strategies developed to access 3,4‐dihydro‐2H‐pyrans, the hetero‐Diels‐Alder reaction between an oxadiene and a dienophile is particularly valuable because up to three contiguous stereogenic centers can be created diastereo‐ and/or enantioselectively in a single step. This review addresses the mechanism of the reaction and presents methods for preparing the product dihydropyrans enantio‐ and diastereoselectively. Thermal and Lewis acid promoted cycloadditions are discussed, as is the role of activating groups on the oxadiene.

This review provides an overview of the applications of α-halogenoacetamides in domino and cycloaddition reactions. α-Halogenoacetamides are versatile building blocks that can lead to a wide variety of complex aza-heterocycles of biological interest when engaged in domino and/or cycloaddition reactions. The reactivity and the reaction conditions involved for these species (solvent, base, etc.) are closely related to the substituent onto the nitrogen atom of the amide: N-alkyl α-halogenoacetamides usually act as formal 1,3-dipoles in domino processes whereas N-alkoxy derivatives often react as real 1,3-dipoles via the formation of aza-oxyallyl cation species. This important modulation of the reactivity of these compounds opens the way to a large panel of reactions and therefore to a large diversity of aza-heterocycles.

In this paper, a new access to several chiral 3-aminoglycals as potential precursors for glycosylated natural products is reported from a common starting material, (−)-methyl-L-lactate. The stereodivergent strategy is based on the implementation of a ring-closing metathesis of vinyl ethers as key step of reaction sequences developed.

A stereospecific Mizoroki-Heck cross-coupling of differently substituted glycals with haloarenes resulting in the exclusive formation of either α- or β-aryl-C-glycosides depending solely on the configuration at C3 was achieved. The reaction was easy to set up because no specific precautions were required concerning moisture or oxygen, and it proceeded by a chirality transfer from C3 to C1. After optimization of cross-coupling conditions, various prepared glycals (7 examples) and arenes (10 examples) were tested, leading stereospecifically to the corresponding aryl-C-glycosides with a carbonyl group at C3, thus opening up new horizons for the total synthesis of glycosylated natural products.

The access to new oxazolo[3,2-d][1,4]oxazepin-5(3H)-ones starting from α-bromoamido alcohols and Michael acceptors under mild conditions is presented. This domino process proved to be chemo-, regio-, and stereoselective and allows the formation of a large diversity of highly functional 7-membered rings in good yields up to 95%. The complete shift of the regioselectivity of the intermediate enolate from a C-C to a C-O bond formation, contrary to the already known alkylations of such ambident nucleophiles, is mostly triggered by steric effects. The last step of the sequence was modeled by DFT giving some important insights for this C-C vs C-O bond shift.

AbstractDie Robinson‐Anellierung hat seit ihrer Entdeckung 1935 in zahlreichen Synthesen Anwendung gefunden, besonders auf dem Gebiet der Steroidsynthese. Die Produkte werden gewöhnlich nach drei aufeinanderfolgenden Stufen erhalten: der Bildung eines Enolats (oder Derivats davon), einer konjugierten Addition und einer Aldolreaktion. Im Laufe der Jahre wurden mehrere methodische Verbesserungen für jede einzelne Stufe vorgenommen oder alternative Synthesewege hin zu Robinson‐Anellierungsprodukten entwickelt. Im ersten Teil dieses Aufsatzes werden die wichtigsten Entwicklungen für die Bildung Monocarbonyl‐abgeleiteter Robinson‐Anellierungsprodukte (MRA‐Produkten, MRAPs) und von einer aktivierten Monocarbonylverbindung abgeleiteter Robinson‐Anellierungsprodukte (AMRA‐Produkten, AMRAPs) erläutert. In den folgenden Abschnitten werden diastereoselektive und enantioselektive Synthesen dieser Produkte beschrieben, und im letzten Abschnitt wird die Racematspaltung von Enantiomerenmischungen dargelegt.

Highly diastereo‐ and enantioselective 1,3‐dipolar cycloadditions between functional ketonitrones and β‐substituted enals are promoted by MacMillan imidazolidinium organocatalysts. A study of the reaction scope shows that high selectivities are conserved if the N‐protecting group or the ester function is varied. However, the reaction is sensitive to steric interactions with the C substituent of the nitrone. In all cases, the reaction proceeds with high exo selectivity. In most cases, a third diastereomer, incompatible with a concerted mechanism, was also observed, albeit in minute amounts. DFT calculations suggest that the cycloaddition proceeds in a nonconcerted fashion by an initial oxa‐Michael‐type addition of the nitrone to the double bond followed by a cyclization. This mechanism explains the formation of the observed minor diastereomers. In addition, the diastereo‐ and enantioselectivities of the reaction were shown to be intermediately thermodynamically controlled, and the diastereomeric ratio is modulated by the kinetics of iminium hydrolysis.