Browse
Submit Data
Databases
API
Help

Dataset Information

22 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Photochemical aryl radical cyclizations to give (E)-3-ylideneoxindoles.

ABSTRACT: (E)-3-Ylideneoxindoles are prepared in methanol in reasonable to good yields, as adducts of photochemical 5-exo-trig of aryl radicals, in contrast to previously reported analogous radical cyclizations initiated by tris(trimethylsilyl)silane and azo-initiators that gave reduced oxindole adducts.

SUBMITTER: Gurry M

PROVIDER: S-EPMC6270804 | biostudies-other | 2014

REPOSITORIES: biostudies-other

ACCESS DATA

Json Xml

Publications

Photochemical aryl radical cyclizations to give (E)-3-ylideneoxindoles.

Gurry Michael M Allart-Simon Ingrid I McArdle Patrick P Gérard Stéphane S Sapi Janos J Aldabbagh Fawaz F

Molecules (Basel, Switzerland) 20140930 10

(E)-3-Ylideneoxindoles are prepared in methanol in reasonable to good yields, as adducts of photochemical 5-exo-trig of aryl radicals, in contrast to previously reported analogous radical cyclizations initiated by tris(trimethylsilyl)silane and azo-initiators that gave reduced oxindole adducts. ...[more]

PMID: 25271428

Similar Datasets

Photochemical Carbene Transfer Reactions of Aryl/Aryl Diazoalkanes-Experiment and Theory*.

Project description:Controlling the reactivity of carbene intermediates is a key parameter in the development of selective carbene transfer reactions and is usually achieved by metal complexes via singlet metal-carbene intermediates. In this combined experimental and computational studies, we show that the reactivity of free diaryl carbenes can be controlled by the electronic properties of the substituents without the need of external additives. The introduction of electron-donating and -withdrawing groups results in a significant perturbation of singlet triplet energy splitting of the diaryl carbene intermediate and of activation energies of consecutive carbene transfer reactions. This strategy now overcomes a long-standing paradigm in the reactivity of diaryl carbenes and allows the realization of highly chemoselective carbene transfer reactions with alkynes. We could show that free diaryl carbenes can be readily accessed via photolysis of the corresponding diazo compounds and that these carbenes can undergo highly chemoselective cyclopropenation, cascade, or C-H functionalization reactions. Experimental and theoretical mechanistic analyses confirm the participation of different carbene spin states and rationalize for the observed reactivity.

| S-EPMC8252492 | biostudies-literature

Photochemical (Hetero-)Arylation of Aryl Sulfonium Salts.

Project description:The construction of (hetero)biaryls, which are ubiquitous scaffolds among medical substances, functional materials, and agrochemicals, constitutes a key application of cross-coupling methods. However, these usually require multiple synthetic steps. Herein, we report a simple photoinduced and catalyst-free C-H/C-H (hetero)arylation cross-coupling through aryl thianthrenium salts, which are formed site-selectively by direct C-H functionalization. The key to this approach is the UV-light, which can disrupt the C-S bond to form thianthrene radical cations and aryl radicals.

| S-EPMC8383302 | biostudies-literature

Photochemical control of DNA structure through radical disproportionation.

Project description:Photolysis of an aryl sulfide-containing 5,6-dihydropyrimidine (1) at 350 nm produces high yields of thymidine and products resulting from trapping of a 5,6-dihydrothymidin-5-yl radical by O? or thiols. Thymidine is believed to result from disproportionation of the radical pair originally generated from C--S bond homolysis of 1 on the microsecond timescale, which is significantly shorter than other photochemical transformations of modified nucleotides into their native forms. Duplex DNA containing 1 is destabilized, presumably due to disruption of ?-stacking. Incorporation of 1 within the binding site of the restriction endonuclease EcoRV provides a photochemical switch for turning on the enzyme's activity. In contrast, 1 is a substrate for endonuclease VIII and serves as a photochemical off switch for this base excision repair enzyme. Modification 1 also modulates the activity of the 10-23 DNAzyme, despite its incorporation into a nonduplex region. Overall, dihydropyrimidine 1 shows promise as a tool to provide spatiotemporal control over DNA structure on the miscrosecond timescale.

| S-EPMC3807129 | biostudies-literature

Aryl radical-mediated N-heterocyclic carbene catalysis.

Project description:There have been significant advancements in radical reactions using organocatalysts in modern organic synthesis. Recently, NHC-catalyzed radical reactions initiated by single electron transfer processes have been actively studied. However, the reported examples have been limited to catalysis mediated by alkyl radicals. In this article, the NHC organocatalysis mediated by aryl radicals has been achieved. The enolate form of the Breslow intermediate derived from an aldehyde and thiazolium-type NHC in the presence of a base undergoes single electron transfer to an aryl iodide, providing an aryl radical. The catalytically generated aryl radical could be exploited as an arylating reagent for radical relay-type arylacylation of styrenes and as a hydrogen atom abstraction reagent for α-amino C(sp3)-H acylation of secondary amides.

| S-EPMC8219674 | biostudies-literature

Radical Aryl Migration from Boron to Carbon.

Project description:Radical aryl migration reactions represent a unique type of organic transformations that involve the intramolecular migration of an aryl group from a carbon or heteroatom to a C- or heteroatom-centered radical through a spirocyclic intermediate. Various elements, including N, O, Si, P, S, Sn, Ge, and Se, have been reported to participate in radical aryl migrations. However, radical aryl migration from a boron center has not been reported to date. In this communication, radical 1,5-aryl migration from boron to carbon in aryl boronate complexes is presented. C-radicals readily generated through radical addition onto alkenyl aryl boronate complexes are shown to engage in 1,5-aryl migration reactions to provide 4-aryl-alkylboronic esters. As boronate complexes can be generated in situ by the reaction of alkenylboronic acid esters with aryl lithium reagents, the aryl moiety is readily varied, providing access to a series of arylated products starting from the same alkenylboronic acid ester via divergent chemistry. Reactions proceed with high diastereoselectivity under mild conditions, and also the analogous 1,4-aryl shifts are feasible. The suggested mechanism is supported by DFT calculations.

| S-EPMC8251698 | biostudies-literature

Photochemical generation and reactivity of the 5,6-dihydrouridin-6-yl radical.

Project description:Nucleobase radicals are the major family of reactive intermediates formed when nucleic acids are exposed to hydroxyl radical, which is produced by gamma-radiolysis and Fe.EDTA. Significant advances have been made in understanding the role of nucleobase radicals in oxidative DNA damage by independently generating these species from photochemical precursors. However, this approach has been used much less frequently to study RNA molecules. Norrish type I photocleavage of the tert-butyl ketone (2b) enabled studying the reactivity of 5'-benzoyl-5,6-dihydrouridin-6-yl (1b). High mass balances were observed under aerobic or anaerobic conditions, and O(2) did not affect the photochemical conversion of the ketone (2b) to 1b. Competition studies with O(2) indicate that the radical abstracts hydrogen atoms from beta-mercaptoethanol with a bimolecular rate constant = 2.6 +/- 0.5 x 10(6) M(-1)s(-1). The major product formed in the presence of O(2) was 5'-benzoyl-6-hydroxy-5,6-dihydrouridine (6). In contrast, 5-benzoyl-ribonolactone (7), a hypothetical product resulting from C1'-hydrogen atom abstraction by the peroxyl radical, could not be detected. Overall, tert-butyl ketone 2b is a clean source of 5'-benzoyl-5,6-dihydrouridin-6-yl (1b) and should prove useful for studying the reactivity of the respective radical in RNA.

| S-EPMC7831383 | biostudies-literature

Photochemical generation and reactivity of the major hydroxyl radical adduct of thymidine.

Project description:5,6-Dihydro-5-hydroxythymidin-6-yl radical (1), the major reactive intermediate resulting from hydroxyl radical addition to C5 of the pyrimidine, is produced via 350 nm photolysis of a 2,5-dimethoxyphenylsulfide precursor (2). Competition between O(2) and thiol for 1 suggests that the radical reacts relatively slowly with β-mercaptoethanol compared to other alkyl radicals. Overall, aryl sulfide 2 should be an effective precursor for the major hydroxyl radical adduct of thymidine in DNA.

| S-EPMC3366351 | biostudies-literature

Metal-Free Radical Borylation of Alkyl and Aryl Iodides.

Project description:A metal-free radical borylation of alkyl and aryl iodides with bis(catecholato)diboron (B2 cat2 ) as the boron source under mild conditions is introduced. The borylation reaction is operationally easy to conduct and shows high functional group tolerance and broad substrate scope. Radical clock experiments and density functional theory calculations provide insights into the mechanism and rate constants for C-radical borylation with B2 cat2 are disclosed.

| S-EPMC6470957 | biostudies-literature

Ascorbic Acid-Initiated Tandem Radical Cyclization of N-Arylacrylamides to Give 3,3-Disubstituted Oxindoles.

Project description:An ascorbic acid-promoted and metal-free tandem room temperature cyclization of N-arylacrylamides with 4-nitrobenzenediazonium generated in situ was developed. This reaction proceeds smoothly through a radical mechanism and provides an environmentally friendly alternative approach to biologically active 3-alkyl-3-benzyloxindoles, avoiding the use of excess oxidants and light irradiation.

| S-EPMC6332015 | biostudies-literature

Photochemical Generation of a Tryptophan Radical within the Subunit Interface of Ribonucleotide Reductase.

Project description:The Escherichia coli class Ia ribonucleotide reductase (RNR) achieves forward and reverse proton-coupled electron transfer (PCET) over a pathway of redox active amino acids (?-Y122 ? ?-Y356 ? ?-Y731 ? ?-Y730 ? ?-C439) spanning ?35 Å and two subunits every time it turns over. We have developed photoRNRs that allow radical transport to be phototriggered at tyrosine (Y) or fluorotyrosine (FnY) residues along the PCET pathway. We now report a new photoRNR in which photooxidation of a tryptophan (W) residue replacing Y356 within the ?/? subunit interface proceeds by a stepwise ET/PT (electron transfer then proton transfer) mechanism and provides an orthogonal spectroscopic handle with respect to radical pathway residues Y731 and Y730 in ?. This construct displays an ?3-fold enhancement in photochemical yield of W(•) relative to F3Y(•) and a ?7-fold enhancement relative to Y(•). Photogeneration of the W(•) radical occurs with a rate constant of (4.4 ± 0.2) × 10(5) s(-1), which obeys a Marcus correlation for radical generation at the RNR subunit interface. Despite the fact that the Y ? W variant displays no enzymatic activity in the absence of light, photogeneration of W(•) within the subunit interface results in 20% activity for turnover relative to wild-type RNR under the same conditions.

| S-EPMC4929995 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data