Themed collection Free Radical Chemistry special themed issue in memory of Athel Beckwith
Effects of geminal methyl groups on the tunnelling rates in the ring opening of cyclopropylcarbinyl radical at cryogenic temperature
Relative enthalpy changes for the two possible modes of ring opening of 2,2-dimethylcyclopropylcarbinyl radical. Tunnelling is indicated by wavy lines.
sulfonyl radical formations from sulfonylhydrazides and oxidative addition to alkenes
Sulfonyl radicals generate from sulfonylhydrazides in the presence of an iron catalyst and air. Addition of resultant radicals to alkenes affords β-hydroxysulfones in good yield.
addition reaction through the homolytic cleavage of a benzylic C–H bond
Direct generation of a benzyl radical by C–H bond activation of toluenes and the addition reaction were developed.
A convenient pathway to Sm(II)-mediated chemistry in acetonitrile
Atom efficient generation of Sm(OTf)2 in acetonitrile provides a stable alternative to SmI2.
Further investigations into the N-demethylation of
oripavine using iron and stainless steel
Further investigations into the direct synthesis of N-nororipavine from oripavine using iron powder under non-classical Polonovski conditions have been conducted. The stoichiometry, solvents and iron oxidation rates were found to have a dramatic effect on the rate of N-demethylation as well as product yield. Herein, we also present high-yield access to the N-demethylated product simply by employing stainless steel rather than iron powder as redox catalyst.
Controlling the action of chlorine radical: from lab to environment
Stable chlorine atom complexes with lignin derivatives may mediate reaction of chlorine atom in the environment and in bleaching facilities.
Block copolymers containing organic semiconductor segments by RAFT polymerization
Vinyl compounds can be transformed to macro-RAFT agents by RAFT single unit monomer insertion providing a route to block copolymers with a short, non-hydrolysable block linkage.
Diastereoselective radical mediated alkylation of a chiral glycolic acid derivative
Radical alkylation of a chiral equivalent of glycolic acid occurs with good to high diastereoselectivity that compares favorably with the corresponding enolate alkylation.
Gas-phase ion-molecule reactions using regioselectively generated radical
cations to model oxidative damage and probe radical sites in peptides
Isomeric radicals of the model peptide Bz-Ala-Gly-OMe can be distinguished via gas phase ion-molecule reactions with O2 and NO2˙. The latter reagent acts as a radical trap to give nitrate esters, whose structures can be distinguished via collision induced dissociation
Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals
What are the factors that influence the effect of substituents on the stability of multiply substituted carbon-centered radicals? This question is addressed with the help of a variety of existing and new thermochemical quantities.
Highly-controlled regiospecific free-
radical copolymerization of 1,3-diene monomers with sulfur dioxide
The free-radical copolymerization of alkyl-substituted 1,3-butadienes with sulfur dioxide produced poly(diene sulfone)s consisting of a highly alternating and 1,4-regiospecific repeating structure.
New domino radical synthesis of aminoalcohols promoted by TiCl4–Zn/t-BuOOH system: selective hydroxyalkylation of
amines in alcohol or in cyclic ether cosolvents
One-pot multicomponent domino radical synthesis of aminoalcohols under mild conditions.
carbonylation of ω-alkynylamines leading to α-methylene lactams. Synthetic scope and the mechanistic insights
Efficient methods for the synthesis of α-methylene lactams were developed based on radical carbonylation and cyclization of ω-alkynylamines.
Photochemical intramolecular cyclization of o-alkynylaryl isocyanides with organic dichalcogenides leading to 2,4-bischalcogenated quinolines
The photochemical cyclization of o-alkynylaryl isocyanides with (RSe)2, (RTe)2, RSH, RSeH, R3GeH, and TTMSS provides a useful tool to access quinoline derivatives.
Kinetic and thermodynamic aspects of the chain-breaking
antioxidant activity of ascorbic acid derivatives in non-aqueous media
Vitamin C lipid-soluble derivatives react with peroxyl radicals at close to diffusion-controlled rate in the dissociated form which has a BDE(OH) lower by 10 kcal mol−1 than the neutral form.
arylation of tyrosine and its application in the synthesis of a highly selective neurotensin receptor 2 ligand
Replacement of (S)-tyrosine by a novel peptide building block led to a high subtype selectivity for the human NTS2 receptor.
Synthesis of the gymnodimine tetrahydrofuran core through a Ueno–Stork radical cyclization
Elaboration of the C10–C20 skeleton of gymnodimine, incorporating a tetrahydrofuran fragment, has been performed through a stereocontrolled Ueno–Stork radical cyclization.
The thermal C2–C6/[2 + 2]
cyclisation of enyne- allenes: Reversible diradical formation
Experimental evidence and computational results suggest that the thermal C2–C6/[2 + 2] cyclisation of enyne-allenes follows a stepwise mechanism involving the reversible formation of the C2–C6 diradical.
oxidation of ferrocenes by short-lived N-oxyl radicals. The role of structural effects on the intrinsic electron transfer reactivities
The role of structural effects on the intrinsic ET reactivities of short-lived N-oxyl radicals have been examined through a kinetic study of the one electron oxidation reactions of substituted ferrocenes
Free radical 5-exo-dig
cyclization as the key step in the synthesis of bis-butyrolactone natural products: experimental and theoretical studies
Radical 5-exo-dig cyclization is used as an entry to bis-butyrolactone natural products with L-ara configuration.
thermal decomposition of N,N-dialkoxyamides
N,N-Dialkoxyamides — unusual anomeric amides. A new PIFA mediated synthesis and studies of their radical homolysis under thermal conditions.
Pyridine as proton acceptor in the concerted proton electron transfer oxidation of phenol
In the presence of pyridine, phenol oxidation occurs concertedly with proton transfer, the charge being delocalized over a primary shell of water molecules bound to the pyridinium cation.
An important role of intramolecular free radical reactions in
antimalarial activity of artemisinin and its analogs
A new mechanism of free radical reactions of artemisinin and its analogs is proposed, where the initiation of hydroxy radicals plays a key role in the antimalarial effect.
Nitroxide biradicals as thread units in paramagnetic
The first example of paramagnetic rotaxane containing cucurbiturils has been reported.
Structural effects on the photodissociation of alkoxyamines
The search for photosensitive alkoxyamines remains a challenge. We investigate the effect of alkoxyamine structure on the photodissociation process.
Intramolecular homolytic substitution of sulfinates and sulfinamides – a computational study
BHandHLYP/6-311++G(d,p) calculations predict that intramolecular homolytic substitution by aryl radicals at the sulfur atom in phenylsulfinates and sulfinamides competes with intramolecular addition to the phenyl ring.
alkylation of guanine derivatives in aqueous medium
The addition of α-hydroxyalkyl radicals to 8-bromoguanine derivatives results in the efficient formation of intermolecular C–C bonds in aqueous media.
Characterization of 2′-deoxyguanosine
oxidation products observed in the Fenton-like system Cu(II)/H2O2/reductant in nucleoside and oligodeoxynucleotide contexts
Copper-mediated Fenton oxidation of 2′-deoxyguanosine leads to predominant formation of 5-carboxamido-5-formamido-2-iminohydantoin (d2Ih) via C5 hydroxylation.
Enantioselective radical cyclisation reactions of 4-substituted
quinolones mediated by a chiral template
Upon association of quinolones to template (+)-1 the chirality information is provided for the enantioselectivity determining cyclisation step.
Linoleic acid peroxidation vs. isomerization: a biomimetic model of free radical reactivity in the presence of thiols
A biomimetic model offers for the first time the parallel estimation of peroxidation and isomerization as results of oxidative free radical conditions in the presence of thiols.
The mechanism of radical-trapping
antioxidant activity of plant-derived thiosulfinates
The ease with which plant-derived thiosulfinates undergo Cope elimination to form the corresponding sulfenic acids accounts for their differences in antioxidant activity.
Ring-opening radical clock reactions: many density functionals have difficulty keeping time
Many density-functional theory methods provide poor agreement to experimental rate constants for the ring opening of radical clock species.
Fragmentations observed in the reactions of α-methoxy-γ-alkoxyalkyl iodide substrates with super-electron-donors derived from 4-DMAP and N-methylbenzimidazole
Interception of alkyl radicals leads to fragmentation, detected by release of alcohols.
Radical-based grafting of GMA on sutures of different nature
The formation of radicals upon high energy irradiation of sutures allows their easy GMA-derivatization.
An ab initio and DFT study of radical addition reactions of imidoyl and thioyl radicals to methanimine
Imidoyl and thioyl radicals add to the nitrogen of methanimine through simultaneous multi-orbital interactions between the radicals and the imine.
A flexible, unified radical-based approach to polycyclic structures
Cis- and trans-decalins, trans-perhydroazulenes, and [5.3.1]bicyclo-undecanone scaffolds can be readily constructed starting from unsaturated ketones and using the degenerative xanthate transfer technology to accomplish unusual and otherwise difficult radical cyclisations
aromatic amino acids by the atmospheric free radical oxidant NO3˙ in the presence of NO2˙, N2O4, O3 and O2
Damage of aromatic amino acids by the most important atmospheric free-radical oxidant, NO3˙, was studied under simulated environmental conditions.
Radical reductions of alkyl halides bearing electron withdrawing groups with
N-heterocyclic carbene boranes
Stable, readily available, low molecular weight N-hetereocyclic carbene boranes reduce halides bearing electron withdrawing substituents. Product isolation is convenient.
Aggregation behaviour of
peptide– polymer conjugates containing linear peptide backbones and multiple polymer side chains prepared by nitroxide-mediated radical polymerization
The synthesis, characterization and studies on aggregation behavior by DLS and AFM of various peptide–polymer conjugates synthesized by NMP are described.
In search of a new class of stable nitroxide: synthesis and reactivity of a peri-substituted N,N-bissulfonylhydroxylamine
Cyclic, peri- and benzo-fused N,N-bissulfonylnitroxides undergo hydrogen atom abstraction in preference to fragmentation.
A stereoselective, Sm(II)-mediated approach to decorated cis-hydrindanes: synthetic studies on faurinone and pleuromutilin
A route to cis–hydrindanes, featuring SmI2-mediated cyclisations, has been used in an RCM approach to analogues of the antibacterial pleuromutilin.
DEPMPO: an efficient tool for the coupled ESR-spin trapping of alkylperoxyl radicals in water
Spin trapping of peroxyl radicals using DEPMPO as the spin trap
Treasures from the Free Radical Renaissance Period – Miscellaneous hexenyl radical kinetic data
Rate constant data and Arrhenius parameters have been determined for a series of substituted hexenyl radicals of differing electronic and steric demand. Rate constants (kcis + ktrans) were found to lie in the range 0.4–2.1 × 105 s−1 at 25°. Cis/trans and kc/kH ratios were found to be solvent dependent.
Kinetic studies of
retinol addition radicals
The dynamics of β-elimination for retinol thiyl addition radicals and their reactions with oxygen were examined for the first time.
Revising the mechanism of
The propagation step of Bolland and Gee's basic autooxidation scheme is not actually thermodynamically favoured for many polymers and biopolymers.
Rate constants for cyclizations of α-hydroxy radical clocks
Rate constants for 5-exo and 6-exo cyclizations of α-hydroxy radicals were measured.
Tandem free-radical addition/substitution chemistry and its application to the preparation of novel AT1 receptor antagonists
Homolytic addition/substitution chemistry has been used to prepare benzoselenophene analogues of the antihypertensive compounds milfasartan and eprosartan. Benzothiophenes were also prepared.
Switching from (R)- to (S)-selective chemoenzymatic DKR of amines involving
sulfanyl radical-mediated racemization
Chemoenzymatic dynamic kinetic resolution of amines involving sulfanyl radical-induced racemization happened to be the very first switchable DKR process allowing the synthesis of either (R)- or (S)-amides.
About this collection
Organic & Biomolecular Chemistry and Carl Schiesser are delighted to publish this very special themed issue on free radical chemistry in memory of Athel Beckwith: a scientific treasure, a gentleman and a wonderful person.
For an introduction to this web themed issue by Carl Schiesser, Guest Editor of this issue see OBC Blog.