Browse
Submit Data
Databases
API
Help

Dataset Information

29 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Photocatalytic Reductive Radical-Polar Crossover for a Base-Free Corey-Seebach Reaction.

ABSTRACT: A metal-free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey-Seebach reaction. The presented method operates under mild redox-neutral and base-free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo- and hydrogen atom transfer (HAT) catalysis. This catalytic merger allows a C-H to carbanion activation by the abstraction of a hydrogen atom followed by radical reduction. The generated nucleophilic intermediate is then capable of adding to carbonyl electrophiles. The obtained dithiane can be easily converted to the valuable ?-hydroxy carbonyl in a subsequent step. The proposed reaction mechanism is supported by emission quenching, radical-radical homocoupling and deuterium labeling studies as well as by calculated redox-potentials and bond strengths.

SUBMITTER: Donabauer K

PROVIDER: S-EPMC7589390 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Photocatalytic Reductive Radical-Polar Crossover for a Base-Free Corey-Seebach Reaction.

Donabauer Karsten K Murugesan Kathiravan K Rozman Urša U Crespi Stefano S König Burkhard B

Chemistry (Weinheim an der Bergstrasse, Germany) 20200917 57

A metal-free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey-Seebach reaction. The presented method operates under mild redox-neutral and base-free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo- and hydrogen atom transfer (HAT) catalysis. This catalytic merger allows a C-H to carbanion activation by the abstraction of a hydrog ...[more]

PMID: 32686166

Similar Datasets

Hydroarylation of Arenes via Reductive Radical-Polar Crossover.

Project description:A photocatalytic system for the dearomative hydroarylation of benzene derivatives has been developed. Using a combination of an organic photoredox catalyst and an amine reductant, this process operates through a reductive radical-polar crossover mechanism where aryl halide reduction triggers a regioselective radical cyclization event, followed by anion formation and quenching to produce a range of complex spirocyclic cyclohexadienes. This light-driven protocol functions at room temperature in a green solvent system (aq. MeCN) without the need for precious metal-based catalysts or reagents or the generation of stoichiometric metal byproducts.

| S-EPMC7667579 | biostudies-literature

Redox-Neutral Photocatalytic Cyclopropanation via Radical/Polar Crossover.

Project description:A benchtop stable, bifunctional reagent for the redox-neutral cyclopropanation of olefins has been developed. Triethylammonium bis(catecholato)iodomethylsilicate can be readily prepared on multigram scale. Using this reagent in combination with an organic photocatalyst and visible light, cyclopropanation of an array of olefins, including trifluoromethyl- and pinacolatoboryl-substituted alkenes, can be accomplished in a matter of hours. The reaction is highly tolerant of traditionally reactive functional groups (carboxylic acids, basic heterocycles, alkyl halides, etc.) and permits the chemoselective cyclopropanation of polyolefinated compounds. Mechanistic interrogation revealed that the reaction proceeds via a rapid anionic 3- exo- tet ring closure, a pathway consistent with experimental and computational data.

| S-EPMC6540794 | biostudies-literature

Photocatalyzed Dowd-Beckwith radical-polar crossover reaction for the synthesis of medium-sized carbocyclic compounds.

Project description:The Dowd-Beckwith reaction, a ring-expansion of carbonyl compounds via alkoxy radicals, is a powerful approach for synthesizing medium to large-sized carbocyclic scaffolds, which takes advantage of existing ring structures and avoids entropic and enthalpic factors that arise from the end-to-end cyclization strategies. However, the Dowd-Beckwith ring-expansion followed by H-atom abstraction is still the dominating pathway, which hampers its synthetic applications, and there currently exist no reports on the functionalization of ring-expanded radicals using non-carbon based nucleophilic reagents. Herein, we report a redox-neutral decarboxylative Dowd-Beckwith/radical-polar crossover (RPC) sequence that delivers functionalized medium-sized carbocyclic compounds with broad functional group tolerance. The reaction allows one-carbon ring-expansion of 4-, 5-, 6-, 7-, and 8-membered ring substrates and can also be applied to three-carbon chain incorporation, enabling remote functionalization in medium-sized rings.

| S-EPMC10306080 | biostudies-literature

Organophotoredox-catalyzed semipinacol rearrangement via radical-polar crossover.

Project description:Over the past century, significant progress in semipinacol rearrangement involving 1,2-migration of α-hydroxy carbocations has been made in the areas of catalysis and total synthesis of natural products. To access the α-hydroxy carbocation intermediate, conventional acid-mediated or electrochemical approaches have been employed. However, the photochemical semipinacol rearrangement has been underdeveloped. Herein, we report the organophotoredox-catalyzed semipinacol rearrangement via radical-polar crossover (RPC). A phenothiazine-based organophotoredox catalyst facilitates the generation of an α-hydroxy non-benzylic alkyl radical followed by oxidation to the corresponding carbocation, which can be exploited to undergo the semipinacol rearrangement. As a result, the photochemical approach enables decarboxylative semipinacol rearrangement of β-hydroxycarboxylic acid derivatives and alkylative semipinacol type rearrangement of allyl alcohols with carbon electrophiles, producing α-quaternary or α-tertiary carbonyls bearing sp3-rich scaffolds.

| S-EPMC9106707 | biostudies-literature

Azido-alkynylation of alkenes through radical-polar crossover.

Project description:We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

| S-EPMC10498506 | biostudies-literature

A Radical-Polar Crossover Annulation To Access Terpenoid Motifs.

Project description:A new catalytic radical-polar crossover annulation between two unsaturated carbonyl compounds is described. The annulation proceeds under exceptionally mild conditions and provides direct and expedient access to complex terpenoid motifs. Application of this chemistry allows for synthesis of forskolin, a densely functionalized terpenoid, in 14 steps from commercially available material.

| S-EPMC7556742 | biostudies-literature

Photocatalytic Reductive Cyclizations of Enones: Divergent Reactivity of Photogenerated Radical and Radical Anion Intermediates.

Project description:Photocatalytic reactions of enones using metal polypyridyl complexes proceed by very different reaction manifolds in the presence of either Lewis or Brønsted acid additives. Previous work from our lab demonstrated that photocatalytic [2+2] cycloadditions of enones required the presence of a Lewis acidic co-catalyst, presumably to activate the enone and stabilize the key radical anion intermediate. On the other hand, Brønsted acid activators alter this reactivity and instead promote reductive cyclization reactions of a variety of aryl and aliphatic enones via a neutral radical intermediate. These two distinct reactive intermediates give rise to transformations differing in the connectivity, stereochemistry, and oxidation state of their products. In addition, this reductive coupling method introduces a novel approach to the tin-free generation of β-ketoradicals that react with high diastereoselectivity and with the high functional group compatibility typical of radical cyclization reactions.

| S-EPMC3222952 | biostudies-literature

Radical-Polar Crossover Annulation: A Platform for Accessing Polycyclic Cyclopropanes.

Project description:Photoredox-mediated radical/polar crossover (RPC) processes provide unique solutions to challenging annulations. Herein, we describe an approach to the cyclopropanation of olefins that are embedded within bicyclic scaffolds. Whereas these systems are notoriously recalcitrant toward classical cyclopropanation approaches, RPC cyclopropanation can be executed with ease, leading to polycarbocyclic and polyheterocyclic cyclopropanes. The cyclopropanation proceeds through a photoredox-enabled Giese-type radical addition followed by an intramolecular anionic substitution reaction on a neopentyl leaving group.

| S-EPMC8172062 | biostudies-literature

Photoredox Radical/Polar Crossover Enables Construction of Saturated Nitrogen Heterocycles.

Project description:Photoredox-mediated radical/polar crossover (RPC) processes offer new avenues for the synthesis of cyclic molecules. This process has been realized for the construction of medium-sized saturated nitrogen heterocycles. Photocatalytically generated alkyl radicals possessing pendant leaving groups engage imines in C-C bond formation, and subsequent reduction of the intermediate nitrogen-centered radical triggers anionic ring closure. With the aid of visible light irradiation, substituted pyrrolidines, piperidines, and azepanes can be prepared under mild, redox-neutral conditions.

| S-EPMC6452489 | biostudies-literature

Dearomatization through Photoredox Hydroarylation: Discovery of a Radical-Polar Crossover Strategy.

Project description:Indole dearomatization has been achieved via radical hydroarylation. Under mild photoredox conditions, a range of indole derivatives undergo hydroarylation to form 2-arylindoline products. Mechanistically, radical termination occurs primarily via stepwise reduction/protonation, with a small contribution from concerted hydrogen atom transfer. This mechanistic understanding prompted the extension of this reactivity to benzenoid dearomatization. This work formed the foundation of our program, which utilizes reductive radical-polar crossover to drive highly selective dearomatization pathways.

| S-EPMC8925927 | 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