Electron spin resonance spectroscopic investigation of carbohydrate radicals. 4. 1,2-Acyloxyl migration in pyranosyl radicals

Korth, Hans Gert; Sustmann, Reiner; Groeninger, K. S.; Leisung, M.; Giese, Bernd

doi:10.1021/jo00253a032

Cited by 109 publications

(53 citation statements)

References 2 publications

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“…61,62 Considerable variation in the A value and the activation energy was observed for these reactions which translates into a spread of rate constants, at a given temperature, over almost two orders of magnitude. To some extent this variation reflects the different ground-state conformations of the initial radicals and the distortion they must undergo to satisfy the stereoelectronic requirements of the migration.…”

Section: Estersmentioning

confidence: 99%

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Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

et al. 1997

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ContentsI. Introduction 3273 II. Rearrangements 3275 A. β-(Acyloxy)alkyl Rearrangement 3275 1. Esters 3275 2. Lactones 3280 3. Thiocarbonyl Esters 3280 B. β-(Phosphatoxy)alkyl Rearrangement 3282 C. β-(Nitroxy)alkyl and β-(Sulfonatoxy)alkyl Rearrangements 3285 D. (Acyloxyalkyl)silyl Radical Rearrangement 3285 III. Fragmentation Reactions 3286 A. β-(Acyloxy)alkyl Radicals and Their Thiocarbonyl Analogues 3286 B. β-(Phosphatoxy)alkyl Radicals 3288 1. Anaerobic Conditions 3288 2. Aerobic Conditions 3293 C. β-(Sulfonatoxy)alkyl and Related Radicals 3294 IV. Mechanism 3294 A. β-(Ester)alkyl Radicals Susceptible to Neither Rearrangement Nor Fragmentation 3294 B. Fragmentation Reactions 3295 C. Rearrangement Reactions 3295 1. Noncage Dissociative Pathways 3296 2. Stepwise Pathways via Five-Membered Cyclic Intermediate Radicals 3296 3. Use of Isotopic and Stereochemical Labeling as Probes of Mechanism 3296 4. Quantitative Structure Activity Relationships 3298 5. Computational Studies and ESR Considerations 3299 V. Overview of β-(Ester)alkyl Radical Reactions 3303 VI. Related Reactions Involving Radical C−O Bond Shift and Cleavage 3305 A. Rearrangement and Fragmentation of β-Hydroxyalkyl Radicals 3305 B. Schenck or Allylperoxy Radical Rearrangement 3307 C. β-(Vinyloxy)alkyl to 4-Ketobutyl Rearrangement 3308 VII. Acknowledgments 3309 VIII. References 3309 Scheme 6

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Section: Estersmentioning

confidence: 99%

“…Also in the context of their ESR investigation, Giese and Sustmann generated and observed radicals 79 and 80 but found no evidence for acyloxy migration. 61 These two failed shifts draw attention to the considerable susceptibility of the rearrangement to fairly subtle changes in radical stability and/or conformation.…”

Section: Estersmentioning

confidence: 99%

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

et al. 1997

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“…A plausible mechanism is provided in Scheme , whereby the anomeric radical 38 undergoes a well‐known 1,2‐shift reported by Giese and colleagues in the carbohydrate field, and the resulting radical 39 abstracts a hydrogen atom from cyclohexane to furnish peracetylated 2‐deoxyglucose 40 and a cyclohexyl radical that propagates the chain. The unexpected feature is the ease and efficiency with which the hydrogen atom abstraction occurs.…”

Section: Polarity Effects On the Rate Of Hydrogen Abstractionmentioning

confidence: 93%

Some intriguing mechanistic aspects of the radical chemistry of xanthates

Zard

2012

J of Physical Organic Chem

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International audienceXanthates are exceedingly useful substrates for intermolecular and intramolecular radical additions, even to unactivated alkenes. Various functional groups can be brought together under mild, neutral conditions, thus providing tremendous opportunities for organic synthesis. Because the products of the additiontransfer process are also xanthates, iteration allows the formation of block polymers by a controlled radical polymerisation (the RAFT/MADIX technology). The present overview concentrates on mechanistic and unexpected aspects of this chemistry, which may be of particular interest to physical organic chemists. Copyright (C) 2012 John Wiley & Sons, Ltd

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“…In this system, inversion of the C-1 ' radical center is observed followed by nucleophilic addition to allyltributyltin, generating the observed product along with a small amount of the addition product arising from unmigrated pivalate. A conceptually related 1,2-acyloxy rearrangement has also been utilized in the syntheses of 2-deoxy-a-glucosides [25].…”

Section: Generation Of A-oxygenated Radicals and Their Subsequent Reamentioning

confidence: 99%

Utilization of α‐Oxygenated Radicals in Synthesis

Buckmelter¹,

Rychnovsky²

2001

Radicals in Organic Synthesis

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@-Oxygenated radical intermediates play an important role in modern synthetic chemistry and the stereochemistry of radical reactions is an area of considerable interest. These intermediates are important in a number of stereoselective transformations, including the radical-mediated syntheses of C-glycosides, 2-deoxy-P-glycosides, spironucleosides, and axial (2-tetrahydropyrany1)lithium and 1-glycosyllithium reagents. Substituted 2-tetrahydropyranyl radicals exhibit anisotropic interactions between the radical center and the adjacent oxygen atom which dictate the stereochemical outcome of these radical reactions. In general, xoxygenated radicals are rapidly equilibrating intermediates, but recent advances have shown that non-equilibrium radical reactions are now possible as a result of the inherent conformational memory present in the radical intermediate. This chapter will focus on the conformations of a-oxygenated (anomeric) radicals in cyclic ethers, the stereoselectivities associated with their reactions, and the applications of these important synthetic intermediates. Conformation and Stereoelectronic Effects of Cyclic a-Oxygenated RadicalsStereoelectronic effects dominate in the reactivities of simple 2-tetrahydropyranyl radicals [I]. In these ring systems, anomeric radicals are best characterized as an equilibrating mixture of pseudoaxial and pseudoequatorial radicals, which tend to be slightly pyramidalized because of the presence of the a-oxygen atom. Moreover, 2-tetrahydropyranyl radicals prefer to be axial in order to maximize overlap with the lone pair of the ring ether oxygen; ab initio calculations predict the axial radical to be >2 kcal/mol more stable than the equatorial radical [2]. In terms of molecular orbital theory, the stabilization between the axial oxygen lone pair and the singly occupied molecular p-orbital (SOMO) of an axial carbon- Radicals in Organic Synthesis Edited by Philippe Renaud andMukund P. Sibi

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Electron spin resonance spectroscopic investigation of carbohydrate radicals. 4. 1,2-Acyloxyl migration in pyranosyl radicals

Cited by 109 publications

References 2 publications

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

Some intriguing mechanistic aspects of the radical chemistry of xanthates

Utilization of α‐Oxygenated Radicals in Synthesis

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