Iron‐Mediated Cyanoalkylsulfonylation/Arylation of Active Alkenes with Cycloketone Oxime Derivatives via Sulfur Dioxide Insertion
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Abstract Iron‐mediated radical cyanoalkylsulfonylation/arylation of active olefins with cycloketone oxime derivatives via cleavage of C−C single bond and insertion of SO 2 is developed for the preparation of cyanoalkylsulfonylated oxindoles. This difunctionalization of carbon−carbon double bond via a radical pathway involves cyclobutanone oxime ester fragmentation, sulfonyl radical generation and radical addition/5‐ exo cyclization. The methodology displays good functional group tolerance and does not require any external bases or oxidants. magnified imageKeywords:
Sulfonyl
Functional group
Cyclobutanone
Radical cyclization
Sulfonyl oxime ethers undergo facile radical substitutions with various amines to yield the corresponding oxime ethers. An efficient arylation of sulfonyl oxime ethers was accomplished under ambient temperature and metal-free conditions, with a wide range of functional group tolerance. Mechanistic investigations indicate that a phenyl radical is involved in the catalytic cycle.
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This article describes the discovery and recent progresses of cyclobutanonebased free radical ring expansion and annulation reactions. Mechanisms associated with these reaction processes are also discussed. Ring expansion reactions rely on selective β- scission of alkoxy radicals generated from the cyclization of carbon radicals onto carbonyls. Exo-substituted cyclobutanones are employed to construct cis-fused seven- and eight-membered rings, spiro-annulated medium rings, large rings, and cyclopropanecontaining compounds. Endo-substituted cyclobutanones can undergo tandem rearrangements to produce bridged rings. The cyclization of dichlorocyclobutanones followed by TMSI-induced ring opening is another ring expansion strategy for the construction of some novel ring systems. Cyclobutanones used for free radical reactions are readily prepared by well-established [2 + 2] cycloadditions of ketenes with various olefins.
Cyclobutanone
Annulation
Radical cyclization
Tandem
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A nickel-catalyzed base-promoted rearrangement of cyclobutanone oxime esters to cyclopropanecarbonitriles was developed. The ring opening of cyclobutanone oxime esters occurs at the sterically less hindered side. A base-promoted nickelacyclobutane intermediate, formed in situ, is assumed to be involved in the formation of the product.
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Beckmann rearrangement
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Abstract Oximierung von D‐Nor‐Soz‐androstanon (I) liefert die isomeren Oxime (II) und (III), deren Gemisch bei Umsetzung mit SOCI, unter Beckmann‐Reaktion die Spaltprodukte (IV) und (V) und die erwarteten Umlagerungsprodukte (VI) und (VII) gibt.
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Beckmann rearrangement
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Cyclobutanone
Radical cyclization
Free-radical reaction
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Abstract A copper‐catalyzed cascade cyclization of 1,6‐enynes with sulfonyl hydrazides for producing various sulfonyl‐substituted γ ‐lactams is described. This sulfonyl radical‐enabled cyclization reaction features excellent regioselectivity, mild conditions and broad substrate scope, enabling the formation of new C−S and C−C bonds through radical sulfonylation, intramolecular cyclization and hydrogen abstraction. Moreover, relevant experiments have been carried out to probe a possible mechanism.
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Hydrogen atom abstraction
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We highlighted the applications of sulfonyl hydrazides in radical cyclization of alkenes, which generally has two radical conversion modes, including sulfonyl radicals and sulfoxide radicals, with an emphasis on their reaction mechanisms.
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Radical cyclization
Radical initiator
Free-radical reaction
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Abstract The 1‐halo‐5‐hexenyl phenyl sulfones (I) undergo radical induced ring closure to yield the cyclopentyl sulfone (IIa), together with the fused thiopyran dioxides (III).
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Tandem
Radical cyclization
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The first example of intramolecular ring-opening and reconstruction of cyclobutanone oxime esters via selective C–C bond cleavage leading to the synthesis of 3,4-dihydronaphthalene-2-carbonitriles in the presence of a cheap copper catalyst has been reported.
Cyclobutanone
Bond cleavage
Cleavage (geology)
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