Radical cyclisation of carbohydrate alkynes: synthesis of highly functionalised cyclohexanes and carbasugars

Maudru, E; Singh, Gurdial; Wightman, R. H.

doi:10.1039/a802228c

Cited by 29 publications

(14 citation statements)

References 21 publications

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“…Premature hydrogen transfers are one way that multiple‐cyclization sequences can be diverted from their original design. For example, attempts by Malacria and co‐workers to synthesize a steroid skeleton by means of a multiple‐cyclization sequence was deflected into a CCH cascade,132 and H migration from supposedly passive ether protecting groups may lead to the formation of dehydroxylated products 133. However, hydrogen migrations can also be beneficial as in the CCCCHC process (followed by elimination of a trimethylsilyl radical) which aided the development of syntheses of linear triquinanes 134…”

Section: Three‐stage and Longer Unimolecular Cascadesmentioning

confidence: 99%

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

McCarroll

Walton

2001

Angew. Chem. Int. Ed.

236

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Cascade, domino, or tandem processes, that link together two or more transformations in one pot, are increasing in popularity because they lead to improvements in synthetic efficiency and decreases in environmental impact. Not only do these cascades contain choice mechanistic gems but they also deliver compact and elegant syntheses of complex natural products. Longer cascades require more functional groups precisely configured within carefully designed initial molecular architectures. Such “purposeful” molecules can be thought of as chemical algorithms.This article surveys the phenomenal range of unimolecular free‐radical cascades. A convenient system for classifying free‐radical cascades is described that is useful for evaluating and comparing cascades and aids the design of synthetic routes to polycyclic structures.Double cyclization cascades lead to cyclopentylcyclopentane or bicyclo[3.3.0]octane derivatives. Precursors that contain a ring as a template have been used to control stereochemistry in syntheses of triquinanes and many related compounds. Of the cascades containing ring‐cleavage steps, the most useful are the ring expansions which have opened up new synthetic routes to medium ring polycycles.The key design features of three‐stage unimolecular free‐radical cascades that yielded steroid structures, are linear arrays of radical acceptor units associated with methyl groups distributed every fifth C‐atom in the precursor polyenes. Ring cleavage is the reverse of cyclization. In special, symmetrical structures, therefore, this led to sequences that were reversible, thus launching endlessly repeating cascades supported by delightfully fluxional structures. The science of “programming” organic molecules to achieve particular target structures is maturing rapidly. Coordination and classification of the welter of information in this area is intended to facilitate design and hence to extend the range and complexity of attainable structures.

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Section: Three‐stage and Longer Unimolecular Cascadesmentioning

confidence: 99%

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

McCarroll

Walton

2001

Angew. Chem. Int. Ed.

236

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“…Enol ethers and oximes can also act as radical acceptors in analogous 6-exo-cyclizations reported by Marco-Contelles [91]. Singh and Wightman [92] recently reported the preparation of carbasugars by 6-exo-dig cyclization of hex-6-ynyl radicals derived from iodides such as 145.…”

Section: Synthesis Of Functionalized Carbocycles By Cyclization Of Acmentioning

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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“…175 The synthesis of carbasugars involving 6-exo-dig radical cyclization was first shown by McDevitt and Fraser-Reid 176 and afterward by Wightman. 177 More recently, Go´mez and Lo´pez have studied the different factors that favor the 6-endo versus 5-exo radical ring clo-sure to lead to carbapyranoses. 178 They found that enyne 150, which includes at least two regiodi-recting features (vinyl radical and substitution at C-5), is able to undergo 6-endo-trig radical cycliza-tion in good yields.…”

Section: Synthesis Of Carbapyranoses and Polyfunctionalized Cyclohexa...mentioning

confidence: 99%

Radicals and Carbohydrates

Pérez‐Martín

Suárez

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

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Radical cyclisation of carbohydrate alkynes: synthesis of highly functionalised cyclohexanes and carbasugars

Cited by 29 publications

References 21 publications

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

Radicals in Carbohydrate Chemistry

Radicals and Carbohydrates

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