Tandem Cyclisations of Amidyl Radicals Derived from O-Acyl Hydroxamic Acid Derivatives

Clark, Andrew J.; Filik, Robert P.; Paecock, Joanne L.; Thomas, Gerard H.

doi:10.1055/s-1999-2641

Cited by 37 publications

(11 citation statements)

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“…Apart from the above, the geminal donor/acceptor N ‐aziridinylimine method of Kim et al,34 and the synthesis of (±)‐ γ ‐lycorane by Zard et al (Section 2.2) are additional examples of the exploitation of N ‐centered radicals. Amidyl radicals have been obtained from N ‐hydroxypyridine‐2‐thione imidate esters (PTOC imidate esters)35 and from O ‐acyl hydroxamic acid derivatives,36 and used in C 5x C 5x cascade cyclizations resulting in hexahydropyrrolizin‐3‐ones such as 30 (Scheme ), containing bridgehead nitrogen atoms.…”

Section: Two‐stage Unimolecular Free‐radical Cascadesmentioning

confidence: 99%

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

McCarroll

Walton

2001

Angew. Chem. Int. Ed.

233

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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: Two‐stage Unimolecular Free‐radical Cascadesmentioning

confidence: 99%

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

McCarroll

Walton

2001

Angew. Chem. Int. Ed.

233

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“…Oxidation of this radical 12, mediated by the CuBr 2 formed in situ from the initial step 1b → 9, followed by elimination of a proton provides the observed oxindole product 8b. 11,12 No sixmembered cyclic sulfonamide 15 was isolated. This is in contrast to Bu 3 SnH-mediated reactions of related sulfonamides where cyclic sulfonamide intermediates were detected.…”

Section: Figurementioning

confidence: 99%

Copper(I) Halide Mediated Tandem 1,4-Aryl Migration-Oxidative Amidyl Radical Cyclisation of Bromosulfonamides

Clark¹,

Fullaway²,

Murphy³

et al. 2009

Synlett

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arylsulfonamides with CuBr/tripyridylamine leads to amidyl radicals via 1,4-aryl migration with concomitant loss of SO 2 , which can further undergo cyclisation to oxindoles or reduction to amides with the ratio dependent upon the temperature and solvent utilised.We recently reported that trichloroacetamide 1 1a and 2-bromo-2-methyl-propionamide 2 1b undergo reaction with copper(I) halides and pentamethyldiethylenetriamine 4 to furnish 2-aryl amides 3a,b via 1,4-aryl migration. At reflux, minor amounts of competing halide reduction to give 2a,b were also observed but levels only became signficant at room temperature (2a/3a = 61:39, 2b/3b = 53:47, Scheme 1). 1,2 Aryl transfer from sulfonamides with loss of SO 2 during radical reactions is well established and a range of migration types including 1,4-and 1,5-aryl migrations have been described. 3 The majority of these published procedures involve reactions mediated by toxic organostannane reagents under high-dilution conditions. Scheme 1 Reaction of amides 1a,b with CuX-4

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“…Darüber hinaus bedient man sich der Stickstoffradikale auch bei der Methode von Kim et al mit dem geminalen Donor/Acceptor N ‐Aziridinylimin34 und bei der Synthese von (±)‐ γ ‐Lycoran nach Zard et al (Abschnitt 2.2). Amidylradikale konnte man aus N ‐Hydroxypyridin‐2‐thionimidatestern (PTOC‐Imidatestern)35 und aus O ‐Acylhydroxamsäurederivaten erhalten36 und in C 5x C 5x ‐Cyclisierungskaskaden einsetzen, wobei Hexahydropyrrolizin‐3‐one wie 30 (Schema ) mit Brückenkopf‐N‐Atomen entstehen.…”

Section: Unimolekulare Zweistufige Radikalische Kaskadenunclassified

Programmierung organischer Moleküle: Design und Management organischer Synthesen über radikalische Kaskaden

McCarroll

Walton

2001

Angew. Chem.

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1. Einleitung 1.1. Beschreibung, Anwendungsbereich und Nutzen von Kaskadenreaktionen Chemische Prozesse, bei denen zwei oder mehr molekulare Veränderungen räumlich und zeitlich eng verknüpft sind (¹Eintopfreaktionenª), wurden als Kaskaden-, Domino-oder Tandemreaktionen oder auch Reaktionsfolgen bezeichnet. Die Wahrnehmung und das chemische Verständnis solcher Prozesse lassen noch zu wünschen übrig, doch das Tempo der Entwicklung ist in letzter Zeit deutlich schneller geworden, da man ihre tatsächlichen und potentiellen Vorteile mehr und mehr erkennt. Mit ihrer Hilfe kann man die Zahl der für den Aufbau eines komplexen Moleküls nötigen Arbeitsschritte im Labor verringern und damit Arbeits-und Gerätezeit sparen und muss weniger Laborplatz beanspruchen. Damit einher geht ein geringerer Verbrauch von Lösungsmitteln und Chemikalien, und es fallen weniger unerwünschte Begleitprodukte an. All diese Faktoren können die Effizienz einer Synthese beträchtlich verbessern und die Umweltbelastung reduzieren. Dieses Potential im Hinblick auf rationelle Synthesen im Labor und im industriellen Maûstab garantiert den Kaskadenprozessen eine glänzende Zukunft.Je gröûer die Zahl der Kaskadenstufen ist, um so mehr Funktionalitäten müssen sich im sorgfältig entworfenen Startmolekül genau an der richtigen Position befinden. Diese Bedingung kann sehr wohl einige der möglichen Vorteile der Kaskadenmethode aufwiegen. Die Struktur der Vorstufe(n) muss sorgfältig ¹programmiertª werden, wenn eine komple-

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Tandem Cyclisations of Amidyl Radicals Derived from O-Acyl Hydroxamic Acid Derivatives

Cited by 37 publications

References 11 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

Copper(I) Halide Mediated Tandem 1,4-Aryl Migration-Oxidative Amidyl Radical Cyclisation of Bromosulfonamides

Programmierung organischer Moleküle: Design und Management organischer Synthesen über radikalische Kaskaden

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