Merging Visible-Light Photoredox Research Articles

Regio- and stereoselective divergent cross-coupling of alkynes and disubstituted alkenes via photoredox cobalt dual catalysis

Regio- and stereoselective divergent cross-coupling of alkynes and gem-disubstituted alkenes has been reported by merging visible light photoredox and cobalt catalysis. The selective ene-type or reductive coupling reaction has been achieved by stwich of different ligands.

Stereoselective Oxidative Mannich Reaction of Ketones with Dihydrodibenzo-Oxazepines via a Merger of Photoredox-/Electro-Catalysis with Organocatalysis.

An enantio- and diastereoselective sp3 -sp3 coupling of acyclic/cyclic ketones with dihydrodibenzo-oxazepines has been developed by merging visible light photo-redox- or electro-catalysis with organocatalysis. This approach parallelly utilizes Eosin Y or graphite electrodes for the co-catalyst-free oxidative conversion of dihydrodibenzo-oxazepines to oxazepines, followed by L-Proline catalyzed direct Mannich-type reaction with ketones. A series of enantioenriched dihydrodibenzo-oxazepines have been prepared in high yields and enantioselectivity. This method shows substantial advantages over the existing protocols by using potentially safer starting materials and cheap commercially available catalysts.

Visible-light photoredox-catalyzed C\u2013O bond cleavage of diaryl ethers by acridinium photocatalysts at room temperature

Cleavage of C–O bonds in lignin can afford the renewable aryl sources for fine chemicals. However, the high bond energies of these C–O bonds, especially the 4-O-5-type diaryl ether C–O bonds (~314 kJ/mol) make the cleavage very challenging. Here, we report visible-light photoredox-catalyzed C–O bond cleavage of diaryl ethers by an acidolysis with an aryl carboxylic acid and a following one-pot hydrolysis. Two molecules of phenols are obtained from one molecule of diaryl ether at room temperature. The aryl carboxylic acid used for the acidolysis can be recovered. The key to success of the acidolysis is merging visible-light photoredox catalysis using an acridinium photocatalyst and Lewis acid catalysis using Cu(TMHD)2. Preliminary mechanistic studies indicate that the catalytic cycle occurs via a rare selective electrophilic attack of the generated aryl carboxylic radical on the electron-rich aryl ring of the diphenyl ether. This transformation is applied to a gram-scale reaction and the model of 4-O-5 lignin linkages.

Visible‐Light‐Promoted Regio‐ and Stereoselective Oxyalkenyl‐ation of Phosphinyl Allenes

AbstractA highly regio‐ and stereoselective oxyalkenylation of phosphinyl allenes is revealed for the first time. This protocol, merging visible light photoredox and palladium catalysis, provides a direct approach to conjugated tertiary allylic alcohol derivatives with broad functional group tolerance in moderate to excellent yields. Mechanistic studies suggest that, although two possible pathways exist in the transformation, radical oxyalkenylation promoted by visible light photoredox takes over the major pathway.magnified image

Merging Visible-Light Photoredox and Chiral Phosphate Catalysis for Asymmetric Friedel-Crafts Reaction with in Situ Generation of N-Acyl Imines.

In the presence of visible-light photoredox and chiral phosphate catalysts, a novel asymmetric Friedel-Crafts reaction of indoles and readily accessible α-amino acid derived redox-active esters is established to afford enantioenriched 1-indolyl-1-alkylamine derivatives in moderate to high yields and with high levels of enantioselectivities. This method not only shows a mild and efficient alternative for the in situ generation of N-acyl imines but also indicates the feasibility of a multicatalyst system for asymmetric photoredox catalysis.

Olefination of Alkyl Halides with Aldehydes by Merging Visible-Light Photoredox Catalysis and Organophosphorus Chemistry

SummaryCarbon-carbon double bond (C=C) formation is a crucial transformation in organic chemistry. Visible-light photoredox catalysis provides economical and sustainable opportunities for the development of novel and peculiar organic reactions. Here we report a method for the olefination of alkyl halides with aldehydes by visible-light photoredox catalysis using triphenylphosphine as a reductive quencher (103 examples). This transformation accommodates a variety of aldehydes including paraformaldehyde; aqueous formaldehyde; 2,2,2-trifluoroacetaldehyde monohydrate; 2,2,2-trifluoro-1-methoxyethanol; and other common aldehydes. The present method exhibits several advantages, including operational simplicity, mild reaction conditions, wide functional group tolerance, and amenability to gram-scale synthesis. We anticipate that it will be widely used in the synthesis of organic molecules, natural products, biological molecules, and polymers.

Merging visible-light photoredox and micellar catalysis: arylation reactions with anilines nitrosated in situ

A micellar photocatalytic system has been disclosed, which enables arylation reactions with anilines nitrosated in situ to run in water.

Acceptorless Dehydrogenation of N-Heterocycles by Merging Visible-Light Photoredox Catalysis and Cobalt Catalysis.

Herein, the first acceptorless dehydrogenation of tetrahydroquinolines (THQs), indolines, and other related N-heterocycles, by merging visible-light photoredox catalysis and cobalt catalysis at ambient temperature, is described. The potential applications to organic transformations and hydrogen-storage materials are demonstrated. Primary mechanistic investigations indicate that the catalytic cycle occurs predominantly by an oxidative quenching pathway.

Merging visible-light photoredox and copper catalysis in catalytic aerobic oxidation of amines to nitriles.

Visible-light-initiated homogeneous oxidative synthesis of nitriles from amines was accomplished through a combined use of photoredox and copper catalysis. This transformation was performed at room temperature with O2 as the oxidant.

Photocatalytic Oxidation of Lignin Model Systems by Merging Visible-Light Photoredox and Palladium Catalysis.

Lignin valorization has long been recognized as a sustainable solution for the renewable production of aromatic compounds. Two-step oxidation/reduction strategies, whereby the first oxidation step is required to "activate" lignin systems for controlled fragmentation reactions, have recently emerged as viable routes toward this goal. Herein we describe a catalytic protocol for oxidation of lignin model systems by combining photoredox and Pd catalysis. The developed dual catalytic protocol allowed the efficient oxidation of lignin model substrates at room temperature to afford the oxidized products in good to excellent yields.

Merging Visible Light Photoredox and Gold Catalysis.

Since the beginning of this century, π-Lewis acidic gold complexes have become the catalysts of choice for a wide range of organic reactions, especially those involving nucleophilic addition to carbon-carbon multiple bonds. For the most part, however, the gold catalyst does not change oxidation state during the course of these processes and two-electron redox cycles of the kind implicated in cross-coupling chemistry are not easily accessible. In order to address this limitation and expand the scope of gold catalysis beyond conventional hydrofunctionalization, extensive efforts have been made to develop new oxidative reactions using strong external oxidants capable of overcoming the high potential of the AuI/AuIII redox couple. However, these processes typically require superstoichiometric amounts of the oxidant and proceed under relatively harsh conditions. Moreover, to date, gold-catalyzed oxidative coupling reactions have remained somewhat limited in scope because, for many systems, the desired cross-coupling does not favorably compete with homodimerization or conventional hydrofunctionalization. In 2013, we disclosed a new concept for gold-catalyzed coupling reactions that, rather than involving external oxidants, employs aryl radicals that act as both the oxidant and the coupling partner in overall redox-neutral transformations. For this, we developed a dual catalytic system combining homogeneous gold catalysis with the emerging field of visible light photoredox catalysis. Using aryldiazonium salts, which are known to act as sources of aryl radicals upon activation with reducing photocatalysts, we could achieve intramolecular oxy- and aminoarylations of alkenes upon irradiating the reaction mixtures with visible light. Further studies on this transformation, in which nucleophilic addition onto a gold-activated alkene is followed by C(sp3)-C(sp2) bond formation, expanded the scope of the process to intermolecular, three-component oxyarylation, while inexpensive organic dyes and user-friendly diaryliodonium salts could be employed as alternative photocatalysts and aryl radical sources, respectively. The potential of dual gold/photoredox catalysis was quickly realized by several research groups and a range of diverse new coupling reactions involving nucleophilic addition to π-systems and even P-H and C(sp)-H functionalization have been developed. In addition to the ambient reaction conditions and the simple setup using household light sources or even sunlight, a key advantage of dual gold/photoredox catalysis results from the simultaneous oxidation of gold(I) and coordination of the coupling partner, which results in high levels of selectivity for the cross-coupled products over homodimers. Furthermore, when gold complexes that are not catalytically active prior to oxidation by the aryl radical are employed, background reactions not involving coupling can be suppressed. Notably, this feature has allowed for the successful use of allenes and alkynes, for which conventional hydrofunctionalization pathways are highly favored, opening the door to new transformations involving the most common substrate classes for gold catalysis. In this Account, we provide an overview of dual gold/photoredox catalysis and highlight the potential of this concept to greatly expand the scope of homogeneous gold catalysis and enable the efficient construction of complex organic molecules. Moreover, recent studies on the visible light-promoted synthesis of novel gold(III) complexes suggest that photoredox activation could yet find further applications in gold chemistry beyond coupling.

ChemInform Abstract: Direct sp3 C—H Acroleination of N‐Aryl‐tetrahydroisoquinolines by Merging Photoredox Catalysis with Nucleophilic Catalysis.

AbstractThe first example of sequence catalysis by merging visible light photoredox catalysis and nucleophilic catalysis is reported.

Merging visible-light photoredox and Lewis acid catalysis for the functionalization and arylation of glycine derivatives and peptides

A relay catalysis protocol for the functionalization of α-amino acids and dipeptides using a combination of visible-light photoredox and Lewis acid catalysis has been developed.