Palladium-Catalyzed Stereoselective Formation of α-<i>O</i>-Glycosides

Schuff, Brandon P.; Mercer, Gregory J.; Nguyen, Hien M.

doi:10.1021/ol071268z

Cited by 50 publications

(42 citation statements)

References 12 publications

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“…207 In his approach, glycosylation of phenol acceptors can be achieved without prior activation by Et 2 Zn(II). However, during reactions involving aliphatic alcohols, an initial conversion to the more reactive zinc alkoxide is necessary.…”

Section: Glycal Donorsmentioning

confidence: 99%

Recent Advances in Transition Metal-Catalyzed Glycosylation

2012

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Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of α- and β-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation.

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Section: Glycal Donorsmentioning

confidence: 99%

Recent Advances in Transition Metal-Catalyzed Glycosylation

2012

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“…Building on our previous successes using cationic transition-metal catalysis for the activation of glycosyl trichloroacetimidate donors in highly-selective glycosylation strategies, [20] we began our search for an appropriate catalyst to facilitate the transformation of α-glycosyl trichloroacetimidate 13 to glycosyl trichloroacetamide 14 with 5 mol% of the readily available Pd(CH 3 CN) 4 (BF 4 ) 2 catalyst (Table 1, entry 1). This system was found to be ill-suited for the conversion, showing no detectable product 14 after 5 h at room temperature.…”

Section: Resultsmentioning

confidence: 99%

“…We then evaluated substrate 36 (Scheme 2b) containing the C 2-azido group, which also led to decomposition. Upon switching to the N -benzylidene protected 2-deoxy glucosamine acetimidates 37 and 38 (Scheme 2c), [20d,e] we were able to efficiently achieve an α-selective transformation (71 – 79%, α/β = 11:1 – 20:1). The Ni(4-F-PhCN) 4 (OTf) 2 catalyst was found to be more reactive that the Ni(dppe)(OTf) 2 catalyst.…”

Section: Resultsmentioning

confidence: 99%

“…[19] Based on our recent efforts using transition-metal catalysis in glycosylation reactions, [20] we envisioned that in the absence of an external nucleophile, a transition-metal catalyst would be able to promote the ionization and subsequent rearrangement of α-glycosyl trichloroacetimidate 10 to the corresponding α-trichloroacetamide 11 (Scheme 1d). [19] The trichloroacetamide intermediates 11 can be directly converted to the c α-glycosyl urea products 12 by reaction with a wide range of amines.…”

Section: Introductionmentioning

confidence: 99%

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Investigations of Scope and Mechanism of Nickel‐Catalyzed Transformations of Glycosyl Trichloroacetimidates to Glycosyl Trichloroacetamides and Subsequent, Atom‐Economical, One‐Step Conversion to α‐Urea‐Glycosides

McKay

Park

Nguyen

2014

Chemistry A European J

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The development and mechanistic investigation of a highly stereoselective methodology for preparing α-linked-urea neo-glycoconjugates and pseudo-oligosaccharides is described. This two-step procedure begins with the selective nickel-catalyzed conversion of glycosyl trichloroacetimidates to the corresponding α-trichloroacetamides. The α-selective nature of the conversion is controlled with a cationic nickel(II) catalyst, Ni(dppe)(OTf)2. Mechanistic studies have identified the coordination of the nickel catalyst with the equatorial C2-ether functionality of the α-glycosyl trichloroacetimidate to be paramount for achieving an α-stereoselective transformation. A cross-over experiment has indicated that the reaction does not proceed in an exclusively-intramolecular fashion. The second step in this sequence is the direct conversion of α-glycosyl trichloroacetamide products into the corresponding α-urea glycosides by reacting them with a wide variety of amine nucleophiles in presence of cesium carbonate. Only α-urea-product formation is observed, as the reaction proceeds with complete retention of stereochemical integrity at the anomeric C-N bond.

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“…Similarly, prior activation of the glycoside acceptor is required via a zinc alkoxide for the reaction to proceed. 35 …”

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confidence: 99%

Palladium-Catalyzed α-Stereoselective O-Glycosylation of O(3)-Acylated Glycals

Galan

2017

Org. Lett.

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Pd(MeCN)2Cl2 enables the α-stereoselective catalytic synthesis of 2,3-unsaturated O-glycosides from O(3)-acylated glycals without the requirement for additives to preactivate either donor or nucleophile. Mechanistic studies suggest that, unlike traditional (η3-allyl)palladium-mediated processes, the reaction proceeds via an alkoxy-palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is exemplified with the synthesis of a range of glycosides and glycoconjugates of synthetic utility.

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Palladium-Catalyzed Stereoselective Formation of α-O-Glycosides

Cited by 50 publications

References 12 publications

Recent Advances in Transition Metal-Catalyzed Glycosylation

Recent Advances in Transition Metal-Catalyzed Glycosylation

Investigations of Scope and Mechanism of Nickel‐Catalyzed Transformations of Glycosyl Trichloroacetimidates to Glycosyl Trichloroacetamides and Subsequent, Atom‐Economical, One‐Step Conversion to α‐Urea‐Glycosides

Palladium-Catalyzed α-Stereoselective O-Glycosylation of O(3)-Acylated Glycals

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