C ‐aryl glycosyl compounds offer better in vivo stability relative to O‐ and N‐ glycoside analogues. C ‐aryl glycosides are extensively investigated as drug candidates and applied to chemical biology studies. Previously, C ‐aryl glycosides are derived from lactones, glycals, glycosyl stannanes, and halides, via methods displaying various limitations with respect to the scope, functional group compatibility, and practicality. Challenges remain in the synthesis of C ‐aryl nucleosides and 2‐deoxysugars from easily accessible carbohydrate precursors. Herein, we report a cross‐coupling method to prepare C ‐aryl and heteroaryl glycosides, including nucleosides and 2‐deoxysugars, from glycosyl esters and bromoarenes. Activation of the carbohydrate substrates leverages dihydropyridine (DHP) as an activating group followed by decarboxylation to generate a glycosyl radical via C–O bond homolysis. This strategy represents a new means to activate alcohols as a cross‐coupling partner. The convenient preparation of glycosyl esters and their stability exemplifies the potential of this method in medicinal chemistry.
Synlett
DOI: 10.1055/a-1349-3543
Nickel-catalyzed carbon–oxygen bond activation is one of the most powerful strategies for the direct construction of various biaryl compounds. Under nickel catalysis, efficiently produced and naturally abundant arenol-based electrophiles can be activated and coupled with different aryl nucleophiles, including nucleophiles containing magnesium, zinc, boron, etc., to produce biaryl structural units. This Account summarizes recent progress on biaryl synthesis via nickel-catalyzed C–O bond activation.1 Introduction2 Coupling of Arenols and Arenol Derivatives with Aryl Magnesium Reagents3 Coupling of Arenols and Arenol Derivatives with Aryl Zinc Reagents4 Coupling of Arenols and Arenol Derivatives with Aryl Boron Reagents5 Others6 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany
Article in Thieme eJournals:
Table of contents | Abstract | Full text
![Nickel‐Catalyzed Acyl Group Transfer of o‐Alkynylphenol Esters Accompanied by C−O Bond Fission for Synthesis of Benzo[b]furan](https://onlinelibrary.wiley.com/cms/asset/50484ebe-bc15-49a1-95b2-5fd942423407/cctc202001949-toc-0001-m.png)
This skeleton lives! Nickel‐catalyzed C−O bond activation of ester and cyclization cascade to construct 3‐acylbenzo[b]furan skeleton is developed. The reaction perfectly avoided the formation of decarbonylated products which was rationalized by density functional theory calculation. Furthermore, the oxidative addition of ester is studied by using a stoichiometric amount of Ni(0)/N‐heterocyclic carbene complex.
Herein, we report the nickel‐catalyzed cascade C−O bond cleavage/cyclization of ortho‐alkynylphenyl ester to construct a 3‐acylbenzo[b]furan skeleton. As a result of reaction condition screening, the Ni(0)/IAd (1,3‐Di(1‐adamantyl)imidazole‐2‐ylidene) system was found to be optimal for catalytic conversion. Interestingly, the reaction exclusively gives 3‐acylbenzo[b]furan instead of a decarbonylated product frequently observed in reactions mediated by acyl‐nickel species. The catalyst loadings could be reduced to 5–10 mol %. We demonstrated the synthesis of a variety of functionalized 3‐acylbenzofuran derivatives. We conducted stoichiometric study of nickel complexes as well as density functional theory (DFT) calculations to support a possible reaction mechanism.
Nature Catalysis, Published online: 08 February 2021; doi:10.1038/s41929-020-00560-3
Mechanistic details of Ni-catalysed functionalizations of strong sigma C–O bonds in synthetic chemistry have been elusive. Now, the identification and characterization of important Ni species, as well as the role of a ZnCl2 additive and solvent in the coupling of aryl esters, are reported.
A Ni‐deposited carbon nitride material was developed as a fully heterogeneous dual photocatalyst. Visible light‐driven C–O cross‐coupling is demonstrated free of organic ligands and additives. This dual catalytic system operates with very low nickel loadings and the heterogeneous photocatalyst can be easily recycled.
Ni‐deposited mesoporous graphitic carbon nitride (Ni‐mpg‐CN x ) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross‐coupling reactions. The dual catalytic Ni‐mpg‐CN x is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good‐to‐excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron‐withdrawing, ‐donating and neutral groups. The heterogeneous Ni‐mpg‐CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.
Open Access
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Shining light on organoborates: A photocatalyzed oxidative cross‐coupling reaction of functionalized organoborates is described, providing a diverse range of biaryl and olefin products. The mechanism of this C−C bond formation was investigated through quantum chemical calculations, revealing an unusual boracyclic intermediate.
Readily accessible tetraorganoborate salts undergo selective coupling reactions under blue light irradiation in the presence of catalytic amounts of transition‐metal‐free acridinium photocatalysts to furnish unsymmetrical biaryls, heterobiaryls and arylated olefins. This represents an interesting conceptual approach to forge C−C bonds between aryl, heteroaryl and alkenyl groups under smooth photochemical conditions. Computational studies were conducted to investigate the mechanism of the transformation.
Better by bio: Dr. Nejad's group has developed a lignin epoxidation method that allows any unmodified lignin (from different biomass sources and extraction processes) to be used for replacing 100 % of toxic bisphenol A (BPA) in the formulation of epoxy resin. A fully bio‐based epoxy system were formulated using lignin, bio‐based epichlorohydrin, and bio‐based hardener, which showed comparable thermomechanical performances to a BPA‐based resin.
Thirteen unmodified lignin samples from different biomass sources and isolation processes were characterized and used to entirely replace bisphenol A (BPA) in the formulation of solubilized epoxy resins using a developed novel method. The objective was to measure the reactivity of different lignins toward bio‐based epichlorohydrin (ECH). The epoxy contents of various bio‐based epoxidized lignins were measured by titration and 1H NMR spectroscopy methods. A partial least square regression (PLS‐R) model with 92 % fitting accuracy and 90 % prediction ability was developed to find correlations between lignin properties and their epoxy contents. The results showed that lignins with higher phenolic hydroxy content and lower molecular weights were more suitable for replacing 100 % of toxic BPA in the formulation of epoxy resins. Additionally, two epoxidized lignin samples (highest epoxy contents) cured by using a bio‐based hardener (Cardolite GX‐3090) were found to show comparable thermomechanical performances and thermal stabilities to a petroleum‐based (DGEBA) epoxy system.
