C-Allylation of 1- and 6-Bromosugars with Allylic Sulfides and Sulfones

Pontén, Fritiof; Magnusson, Göran

doi:10.1021/jo960749l

Cited by 39 publications

(14 citation statements)

References 15 publications

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“…Preparation of C-glycofuranosides by intermolecular addition of glycofuranos-1 -yl radicals to C=C cosy1 bromide 5 with the allyltin reagent 23 was biomimic of the enzymatic aldol reactions reactions between phosphoenol pyruvate and carbohydrates. Glycosyl radical donors similarly undergo stereoselective allylation with allylic sulfides and sulfones [29]. Glycos-1 -yl radicals may undergo dimerization in the absence of an intermolecular trap.…”

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confidence: 99%

Radicals in Carbohydrate Chemistry

Pearce¹,

Mallet²,

Sînaÿ³

2001

Radicals in Organic Synthesis

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Radical methods are of central importance in organic synthesis [ 11. These reactions are performed under mild and neutral conditions, which usually avoids competing ionic side reactions. Carbon-centered radicals are compatible with a range of functional groups (e.g. aliphatic alcohols, amines, ketones, esters) and also show high chemoselectivity under carefully controlled reaction conditions. Furthermore, reactions involving loss of stereochemistry at the non-radical center are not problematic, and hence radical methods are emerging as a powerful synthetic tool in the field of carbohydrate chemistry.In this article we provide a broad overview of the application of radical methods in carbohydrate chemistry, including typical examples classified by the type of bond formed. The factors controlling the stereoselectivity of inter-and intramolecular C-C bond formation are now well understood and have been exploited in the synthesis of C-glycosides [2]. Intramolecular C-C bond formation using carbohydratebased chiral templates also provides a powerful route to branched-chain sugars [ 3 ] and carbocycles [4]. Finally, we include synthetically useful processes involving key carbon-heteroatom and C-H bond formation. Intermolecular Carbon-Carbon Bond Formation Synthesis of C-GlycosidesA powerful strategy for the formation of C-glycosides is the intermolecular addition of an anomeric radical to n-systems [2]. Anomeric pyranosyl radicals are readily generated by a variety of standard methods and are nucleophilic in character because of interaction of the SOMO with the non-bonding electron pair of the adjacent ring oxygen. Anomeric radicals therefore undergo addition to n-systems when the high-lying SOMO can interact with a low-lying LUMO as in electron-deficient Radicals in Organic Synthesis Edited

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confidence: 99%

Radicals in Carbohydrate Chemistry

Pearce¹,

Mallet²,

Sînaÿ³

2001

Radicals in Organic Synthesis

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“…In our hands the reaction was complicated by low yields (<30%) and significant contamination by the β-isomer. We thus turned to the radical protocol of Magnusson and co-workers . Photochemically initiated allylation of acetobromolactose ( 1 ) with allyl phenyl sulfone and bistributyltin afforded the desired α-analogue 2 exclusively, but in only moderate yield (∼50%).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of α- and β-Carbon-Linked Serine Analogues of the P^k Trisaccharide

1999

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The synthesis of glycopeptide ligands for a range of biomedically relevant carbohydrate-binding proteins is a topic of great importance to the glycobiology community. This task is impeded by the inherent instability of glycosyl linkages to serine/threonine, the normal sites of O-glycosylation in proteins. We have previously developed methodology for the preparation of C-glycosylated serines based on catalytic asymmetric hydrogenation of the corresponding enamide esters with the DuPHOS−Rh+ catalysts. Here we report further development of the methodology in the preparation of the C-glycosyl serine analogue of the Pk trisaccharide (α-Gal(1→4)β-Gal(1→4)β-Glc-CH 2 -serine); we require these ligands for our continuing investigations of the binding subunit of the shiga-like toxin. Catalytic asymmetric hydrogenation was used to prepare both α- and β-C-glycosides in the R and S serine series. We report here on the tolerance of the DuPHOS catalysts toward acetate, benzoate, and benzyl hydroxyl protecting groups. Additionally, we have developed an amino acid protecting group strategy compatible with both asymmetric hydrogenation and solid-phase peptide synthesis. In the course of our studies, we have also developed a new methodology for regioselective reductive cleavage of benzylidene protecting groups.

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“…Thus, the ultraviolet (UV) irradiation of α-d-galactopyranosyl bromide with allylic sulfides and sulfones in the presence of hexabutylditin gave the corresponding 3-C-(α-d-galactopyranosyl)-1-propene derivatives with excellent diastereoselectivity. 30 d-Gluco-1-yl radicals can also be generated by reaction of d-glucosyl iodide 9 with 1-ethyl-…”

Section: Synthesis Of C-glycosidesmentioning

confidence: 99%