Synthesis of β-<i>C</i>-Glycosides of <i>N</i>-Acetylglucosamine via Keck Allylation Directed by Neighboring Phthalimide Groups

Roe, Barbara A.; Boojamra, Constantine G.; Griggs, Jennifer L.; Bertozzi, Carolyn R.

doi:10.1021/jo960819o

Cited by 82 publications

(29 citation statements)

References 34 publications

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“…13.2) and can be rationalized by additive anomeric and quasi-homo-anomeric effects (model 17). Bertozzi has reported a very elegant approach to CI-and p-C glycosides of Nacetylglucosamine via tin-mediated radical allylation (Scheme 14) [38]. The stereochemical outcome of the reaction was essentially controlled by the anomeric effect when the N-acetyl derivative was used (alp 1O:l).…”

Section: Stereoelectronic Effectsmentioning

confidence: 99%

Stereoselectivity of Radical Reactions: Cyclic Systems

Renaud¹

2001

Radicals in Organic Synthesis

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Cyclic radicals are very often involved in the key step of a reaction sequence. They are particularly useful since the stereochemical outcome of their reactions can be easily predicted and in some cases directed. Selected examples from the recent literature have been chosen in order to illustrate the different factors governing the stereochemical outcome. The importance of steric effects, conformational effects, neighboring prochiral centers, pyramidalization, stereoelectronic effects and position of the transition states will be discussed based on examples of synthetic importance. The anti RuleCyclic radicals can only exist in a reduced number of conformations relative to acyclic ones. Therefore, prediction of the stereochemistry is simplified. As nicely documented in two excellent review articles [ l , 21, the anti rule could be applied with great success to many cases of cyclic radicals: reactions occur preferentially in unti fashion to the substituents present in the cyclic moiety. This simple model is based on minimization of steric interactions in the transition state and is particularly efficient when the conformation of the radical intermediate is known.

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Section: Stereoelectronic Effectsmentioning

confidence: 99%

Stereoselectivity of Radical Reactions: Cyclic Systems

Renaud¹

2001

Radicals in Organic Synthesis

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“…The C-ally1 glycosides of N-acetylneuraminic acid 20 [26] and N-phtalimidoglucosamine 21 [27] have been prepared by this method and are important targets for the design of C-linked glycopeptide mimetics. The reaction is also extended to branched derivatives such as methallyltributyltin 22 [28] and 23 [ lo], although substitution at the terminal position of allyltributyltin in not tolerated.…”

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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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“…356 Thus, starting from precursor 81, the tetra-acetyl 2-tetrachlorophthalimido derivative 148 is obtained in 56% yield over three steps (Scheme 27). 443 Precursor 148 can then be modified accordingly into potent glycosyl donors such as bromides, 202,444,445 fluorides, 441 pentenyl ethers, 352,353,443,446 trichloroacetimidates, 438,447 or thioglycosides. [448][449][450] Herein, the synthesis and application of trichloroacetimidate 149 and O-pentenyl glycoside 153 synthesized via bromide 152 will be discussed.…”

Section: Disubstituted 2-amino-2-deoxyglycosyl Donorsmentioning

confidence: 99%