Mild Cu(OTf)2-Mediated C-Glycosylation with Chelation-Assisted Picolinate as a Leaving Group

Reagent-assisted regio-divergent cyclization synthesis of pyrazole

The present study reveals a practical one-pot base-promoted regio-divergent cyclization of hydrazines with alkynyl silane under mild conditions, facilitating the synthesis of diverse silicone-substituted pyrazoles and functionalized pyrazoles in great yields with exceptional selectivity. This protocol is expected to afford a streamlined one-pot approach for the synthesis of multiple compounds in water.

[Au]/[Ag]-catalysed synthesis of non-hydrolysable C-glycosides

Many C-glycosides are found in natural products, drugs and small molecular probes. Herein, we report the synthesis of C-glycosides by the [Au]/[Ag]-catalysed activation of ethynylcyclohexyl glycosyl carbonate donors. This mild, catalytic, fast and high yielding protocol enables the synthesis of a diverse array of C-glycosides that were otherwise challenging to synthesize.

C-OH Bond Activation for Stereoselective Radical C-Glycosylation of Native Saccharides

Radical C-glycosylation presents a flexible and efficient method for synthesizing C-glycosides. Existing methods always require multistep processes for generating anomeric radicals. In this study, we introduce a streamlined approach to produce anomeric radicals through direct C-OH bond homolysis of unmodified saccharides, eliminating the need for protection, deprotection, or activation steps. These anomeric radicals selectively couple with activated alkenes, yielding C-glycosylation products with high stereoselectivity (>20:1). This method is applicable to a variety of native monosaccharides, such as l-arabinose, d-arabinose, d-xylose, l-xylose, d-galactose, β-d-glucose, α-d-glucose, and l-ribose, as well as oligosaccharides including α-lactose, d-(+)-melibiose, and acarbose. We also extend this approach to C-glycosylation of amino acid and peptide derivatives, and demonstrate a streamlined synthesis of an anti-inflammatory agent.

Photocatalytic Synthesis of α-Ketonyl Glycosyl Compounds from Glycosyl Thiols and Silyl Enol Ethers

The synthesis of C1-ketonyl glycosyl compounds featuring α-selectivity has seldom been reported. We herein devise a glycosyl radical-based approach to facilely access stereoenriched ketonyl glycosyl compounds via an Ir photoredox-catalyzed desulfurative addition to silyl enol ethers, using in situ-generated tetrafluoropyridinyl thioglycosides from glycosyl 1-thiols as radical precursors. This protocol features readily prepared starting materials, mild conditions, excellent functional group tolerance, satisfactory scale-up, and notable amenability to late-stage modification of pharmaceutically relevant complex molecules.

Excited-State Palladium-Catalyzed α-Selective C1-Ketonylation

C-Glycosides are important carbohydrate mimetics found in natural products, bioactive compounds, and marketed drugs. However, stereoselective preparation of this class of glycomimetics remains a significant challenge in organic synthesis. Herein, we report an excited-state palladium-catalyzed α-selective C-ketonylation strategy using readily available 1-bromosugars to access a range of C-glycosides. The reaction features excellent α-selectivity and mild conditions that tolerate a wide range of functional groups and complex molecular architectures. The resulting α-ketonylsugars can serve as versatile precursors for their β-isomers and other C-glycosides. Preliminary experimental and computational studies of the mechanism suggest a radical pathway involving the formation of palladoradical and glycosyl radical that undergoes polarity-mismatched coupling with silyl enol ether, affording the desired α-ketonylsugars. Insight into the reactivity and mechanism will inspire new reaction development and provide straightforward access to both α- and β-C-glycosides, greatly expanding the chemical and patent spaces of glycomimetics.

Visible-Light-Induced Copper-Catalyzed Asymmetric C(sp3)-C(sp3)-H Glycosylation: Access to C-Glycopeptides

Herein, a practical and highly efficient method for visible-light-induced copper-catalyzed N-aminoquinoline-directed asymmetric C(sp³)-C(sp³)-H glycosylation was reported. At the same time, C(sp³)-C(sp³)-H glycosylation of nondeoxysugars with amino acids to construct C-glycopeptides was achieved. This approach promoted the synthesis of various C-glycopeptides and provided a new model for the synthesis of C-glycoamino acids.

Glycosyl 3-Phenyl-4-pentenoates as Versatile Glycosyl Donors: Reactivity and Their Application in One-Pot Oligosaccharide Assemblies

Both glycoconjugates and oligosaccharides are important biomolecules having significant roles in several biological processes, and a new strategy for their synthesis is crucial. Here, we report a versatile N-iodosuccinimide/trimethylsilyl triflate (NIS/TMSOTf) promoted glycosidation approach with shelf-stable 3-phenyl-4-pentenoate glycosyl as a donor for the efficient synthesis of O/C-glycosides with free alcohols, silylated alcohols, and C-type nucleophile acceptors in good to excellent yields. The mild activation conditions and outstanding reactivity of phenyl substituted pentenoate donors analogous to 4-pentenoate glycosyl donors enhance their applicability to various one-pot strategies for the synthesis of oligosaccharides, such as single-catalyst one-pot and acceptor reactivity-controlled one-pot strategies.

Transition metal catalyzed glycosylation reactions - an overview

Carbohydrates are a large class of natural products that play key roles in a number of biological processes such as in cellular communication or disease progression. Carbohydrates are also used as vaccines and pharmaceuticals. Their synthesis through glycosylation reactions is challenging, and often stoichiometric amounts of promoters are required. Transition metal catalyzed glycosylation reactions are far less common, but can have advantages with respect to reaction conditions and selectivity. The review intends to approach the topic from the catalysis and carbohydrate perspective to encourage researchers from both the fields to perform research in the area. The article covers the basics in glycosylation and catalysis chemistry. The catalysts for the reaction can be roughly divided into two groups. In one group, the catalysts serve as Lewis acids. In the other group, the catalysts play a higher sophisticated role, are involved in all elementary steps of the mechanism and remain coordinated to the substrate throughout the whole catalytic cycle. Based on selected examples, the main trends in transition metal catalyzed glycosylation reactions are explained. Lewis acid catalysts tend to require a somewhat higher catalyst load compared to other organometallic catalysts. The reaction conditions such as the temperature and time depend in many cases on the leaving group employed. An outlook is also presented. The article is not meant to be comprehensive; it outlines the most common transition metal catalyzed processes with the intention to bring the catalysis and carbohydrate communities together and to inspire research activities in both areas.