Synthesis of pyrrolizidines by cascade reactions of N-alkenylaziridinylmethyl radicals

Smaele, Dirk De; Bogaert, Piet; Kimpe, Norbert De

doi:10.1016/s0040-4039(98)02176-5

Cited by 34 publications

(10 citation statements)

References 19 publications

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“…A second cyclization onto the vinyl group took place with the cis ‐isomer of the intermediate vinyl tetrahydrofuranylmethyl radical ( F 3 C 5x C 5x ) opening the way to 7‐oxabicyclo[2.2.1]heptane derivatives. More recently, another FC reaction involving a homoallylic aminyl radical derived from an aziridinylmethyl radical has been described 112…”

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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“…A limited number of additions to azides and azo acceptors have also appeared [4]. The fragmentation reaction of aziridinylmethyl radical has been used recently to generate allylaminyl radical, which participates in cascade reactions [70]. The selected transformations shown in Table 7 are illustrative of the scope of these reactions.…”

Section: From Some Other Sourcesmentioning

confidence: 99%

Nitrogen‐Centered Radicals

Stella¹

2001

Radicals in Organic Synthesis

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A wide variety of useful organic transformations involve N-centered radicals. Two of the most characteristic inter-and intramolecular reactions of N-centered radicals are selective hydrogen abstraction and amination of unsaturated substrates (olefinic or aromatic). Hydrogen abstraction is a reaction in which an alkane C-H (T bond is cleaved. The resulting C-centered radical generally combines with a halogen atom donor, in a chain mechanism, to form a carbon-halogen bond. Aminations of olefinic or aromatic substrates are reactions in which N-centered radicals add to the system of a carbon-carbon double bond to form a carbon-nitrogen bond and a Ccentered radical, which is generally removed by atom or group transfer reaction in a chain mechanism. Both these types of intramolecular reaction are particularly useful for heterocyclic synthesis.A comprehensive review of N-centered radical reactions appeared in 1973 [ 11, and the aminium radical chemistry has also been thoroughly reviewed in 1980 [2]. Other reviews, some dealing with specific sub-areas, have been published throughout the last thirty years [3-131. It is the aim of this report to survey the more important developments in the area of synthetic applications and to summarize how a practicing organic chemist can expand the classical repertoire of synthetic methods by using N-centered radical reactions. No attempt has been made to present an exhaustive review of the literature, but, rather, a few specific examples without excessive details are discussed to demonstrate the key features. Basic PrinciplesAminyl radicals are less reactive than carbon radicals, which in turn are less reactive than alkoxy radicals. For dialkylaminyl radicals, the reduction rate constant with tributyltin hydride ( k~ % 5 x lo5 M-' s-' ) [I41 is about ten times lower than for primary alkyl radicals [15] and a thousand times lower than for alkoxy radicals [ 161. Radicals in Organic Synthesis Edited by Philippe Renaud and Mukund P. Sibi

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“…Eine zweite Cyclisierung mit Ringbildung an die Vinylgruppe geschieht beim cis ‐Isomer des als Zwischenstufe gebildeten Vinyltetrahydrofuranylmethylradikals ( F 3 C 5x C 5x ); dies eröffnet den Weg zu 7‐Oxabicyclo[2.2.1]heptanderivaten. Kürzlich wurde eine weitere FC ‐Reaktion mit einem homoallylischen Aminylradikal beschrieben, das aus einem Aziridinylmethylradikal entstand 112…”

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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Synthesis of pyrrolizidines by cascade reactions of N-alkenylaziridinylmethyl radicals

Cited by 34 publications

References 19 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

Nitrogen‐Centered Radicals

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

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