Some intriguing mechanistic aspects of the radical chemistry of xanthates

Zard, Samir Z.

doi:10.1002/poc.2976

Cited by 26 publications

(21 citation statements)

References 68 publications

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“…This gap in synthesis has now been largely filled by a reaction we discovered some time ago. It is based on the degenerative xanthate transfer depicted in greatly simplified form in scheme 10 [30,31].…”

Section: Methodsmentioning

confidence: 99%

Some aspects of radical cascade and relay reactions

Quiclet‐Sire¹,

Zard²

2017

Proc. R. Soc. A.

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The ability to create carbon-carbon bonds is at the heart of organic synthesis. Radical processes are particularly apt at creating such bonds, especially in cascade or relay sequences where more than one bond is formed, allowing for a rapid assembly of complex structures. In the present brief overview, examples taken from the authors' laboratory will serve to illustrate the strategic impact of radical-based approaches on synthetic planning. Transformations involving nitrogen-centred radicals, electron transfer from metallic nickel and the reversible degenerative exchange of xanthates will be presented and discussed. The last method has proved to be a particularly powerful tool for the intermolecular creation of carbon-carbon bonds by radical additions even to unactivated alkenes. Various functional groups can be brought into the same molecule in a convergent manner and made to react together in order to further increase the structural complexity. One important benefit of this chemistry is the so-called RAFT/MADIX technology for the manufacture of block copolymers of almost any desired architecture.

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Section: Methodsmentioning

confidence: 99%

Some aspects of radical cascade and relay reactions

Quiclet‐Sire¹,

Zard²

2017

Proc. R. Soc. A.

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“…1:1 in both cases). [29,30] A little later, Vidal and co-workers noted that benzylic xanthate 22 afforded a quantitative yield of dibenzyl 23 upon exposure to stoichiometric peroxide. [31] What is surprising is not the formation of dimers in a radical process.…”

Section: Preamblementioning

confidence: 99%

Radical Alliances: Solutions and Opportunities for Organic Synthesis

Zard

2019

Helvetica Chimica Acta

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The present account discusses in detail various mechanistic features of the degenerative radical addition‐transfer of xanthates and related thiocarbonylthio congeners and makes a comparison with the more classical Kharasch reactions to which it is similar in certain aspects. The xanthate group reacts reversibly with the ‘active’ radicals in the medium and is able to store them in a somewhat inactive form. This increases their effective lifetime in the medium and, at the same time, lowers their absolute concentration while regulating their relative concentration. These properties translate into a powerful carbon–carbon bond forming process, especially as regards intermolecular additions to electronically unbiased (‘unactivated’) alkenes. Most functional groups are tolerated, in particular polar functions that often require protection with other chemistries. This broad versatility is illustrated by examples where the xanthate addition to the alkene is combined with other, more classical reactions to provide a convergent, rapid access to a wide range of useful structures. Emphasis has been placed on the synthesis of open chain and more complex carbocycles, as well as on the transfer of chirality. These ‘radical alliances’ include organosilicon chemistry, the Diels–Alder cycloaddition and cheletropic extrusion of sulfur dioxide, the Claisen sigmatropic rearrangement, and the Horner–Wadsworth–Emmons (HWE) condensation.

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“…The reaction manifold in Scheme has many other interesting subtle features, which will not be discussed here (a more thorough description of the mechanism can be found in Refs. ). There are nevertheless various practical advantages that must be pointed out.…”

Section: Mechanism and Selected Examplesmentioning

confidence: 99%

On the Strategic Impact of the Degenerative Transfer of Xanthates on Synthetic Planning

Quiclet‐Sire

Zard

2016

Israel Journal of Chemistry

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The present brief account relates synthetic endeavours revolving around a novel chemistry of xanthates (dithiocarbonates) being developed in our group. The degenerative reversible transfer of xanthates has a unique ability to store reactive radicals in a dormant form, and thereby to enhance their lifetime in a concentrated medium, while at the same time, regulating their absolute and relative concentrations. It allows intermolecular radical additions even to unactivated alkenes, and can promote otherwise sluggish radical processes, such as 5‐endo, 6‐exo, 6‐endo, 7‐endo, and 8‐endo cyclisations, as well as ring closures on (hetero)aromatic structures. This chemistry has proved remarkably versatile and powerful, both for solving synthetic problems and for the industrial production of block copolymers through the RAFT/MADIX technology.

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Some intriguing mechanistic aspects of the radical chemistry of xanthates

Cited by 26 publications

References 68 publications

Some aspects of radical cascade and relay reactions

Some aspects of radical cascade and relay reactions

Radical Alliances: Solutions and Opportunities for Organic Synthesis

On the Strategic Impact of the Degenerative Transfer of Xanthates on Synthetic Planning

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