Direct enantioselective reduction of C=C bond of β-polyfluoro-alkylated enones via asymmetric photoredox catalysis

Direct enantioselective reduction of the C=C bond ofβ-polyfluoro-alkylated enones is an important but long-pending subject in asymmetric catalysis.Here,we report on the viability of visible light-driven cooperative photoredox and chiral hydrogenbonding catalysis to effectively address this challenge,as a variety of products are obtained in high yields(up to 85%)with good to excellent enantioselectivities(up to 98%ee).The formation of thermodynamically favorable enol intermediates after double single-electron reduction represents the center of the success.Additionally,the utility of the current method is validated by the convenient regio-specific and-diverse synthesis of various deuterated derivatives for these products using inexpensive D_(2)O as the deuterium source.

Modular synthesis of 1,4-diketones through regioselective bis-acylation of olefins by merging NHC and photoredox catalysis

Efficient and modular synthesis of structurally diverse 1,4-diketones from readily available building blocks represents an essential but challenging task in organic chemistry.Herein,we report a multi-component,regioselective bis-acylation of olefins by merging NHC organocatalysis and photoredox catalysis.With this protocol,a broad range of 1,4-diketones could be rapidly assembled using bench-stable feedstock materials.The robustness of this method was further evaluated by sensitivity screening,and good reproductivity was observed.Moreover,the diketone products could be readily converted into functionalized heterocycles,such as multi-substituted furan,pyrrole,and pyridazine.Mechanistic investigations shed light on the NHC and photoredox dual catalytic radical reaction mechanism.

Chlorine Atom Transfer of Unactivated Alkyl Chlorides Enabled by Zirconocene and Photoredox Catalysis

Alkyl chlorides are robust precursors to carbon radicals;however,their relative inertness has hampered their practical use.Although modern photochemical strategies have greatly enhanced the utility of alkyl chlorides as radical precursors,these methods often depend on strongly reducing conditions leading to unproductive side reactions.Here,we report a catalytic radical generation from 1°,2°,and 3°unactivated alkyl chlorides with zirconocene and photoredox catalysis,which enables both hydrogenation and borylation on a range of structurally complex molecules.This mild zirconocene-catalyzed protocol shows that zirconium can render the C−Cl bond cleavage more exergonic and can lower the activation energy of the transition state,amplifying the ability of metallocenes toward halogen atom transfer.

A review of enantioselective dual transition metal/photoredox catalysis

Transition metal catalysis is one of the most important tools to construct carbon-carbon and carbon-heteroatom bonds in modern organic synthesis. Visible-light photoredox catalysis has recently drawn considerable attention of the scientific community owing to its unique activation modes and significance for the green synthesis. The merger of photoredox catalysis with transition metal catalysts, termed metallaphotoredox catalysis, has become a popular strategy for expanding the synthetic utility of visiblelight photocatalysis. This strategy has led to the discovery of novel asymmetric transformations, which are unfeasible or not easily accessible by a single catalytic system. This contemporary area of organic chemistry holds promise for the development of economical and environmentally friendly methods for the asymmetric synthesis of chiral compounds. In this review, the advances in the enantioselective metallaphotoredox catalysis(EMPC) are summarized.

Valorization of Biomass-Derived Platform Molecules via Photoredox Sustainable Catalysis

The conversion of biomass into valuable chemicals has promise for application in biorefineries.Light-driven photoredox catalysis,with the typical features of green route and operation under mild conditions,is considered a promising strategy for renewable biomass or biomass-derived intermediates conversion into high-value-added chemical feedstocks.In this review,we strongly emphasize the recent advances in photocatalytic valorization of lignin model compounds and biomassderived alcohols.We briefl y summarize the advances in photocatalytic cleavage of theβ-O-4 bond or C–C bond into usable chemicals in the lignin model.On the other hand,we clarify not only the hybrid system for cooperative biomass-relevant alcohols oxidation and hydrogen(H2)evolution but also the tunable accessibility to variation of the target products from the same alcohol reactant by catalyst design and optimization of reaction conditions.It is hoped that this review will inspire the rational design of photoredox catalysis-based systems toward efficient biomass-derived platform molecules valorization to obtain target-oriented valuable products.

Chemistry With N-Centered Radicals Generated by Single-Electron Transfer-Oxidation Using Photoredox Catalysis

This review covers the recent literature on oxidative generation of N-centered radicals using photoredox catalysis.The concept of proton-coupled electron transfer is briefly discussed.Applications of such reactive N-centered radicals in cascade processes comprising arene amidation,alkene amidation,C—C bond cleavage reactions,and remote C—H functionalization are addressed.In addition,novel reagents allowing for clean oxidative N-radical generation are discussed.

Photoredox Catalysis Unlocks the Nickel-Catalyzed Cyanation of Aryl Halides under Benign Conditions

The transition-metal-catalyzed cyanations of aryl halides are among the most used methods for synthesizing aryl nitriles.Despite tremendous advances,cyanating an aryl halide in a facile and benign fashion has generally been unsuccessful.The challenge in this significant transformation is the strong affinity of cyanide for metals,which hampers oxidative addition(OD)and reductive elimination(RE)making organometallic catalysis elusive.Herein,we demonstrate for the first time that photoredox-nickel-catalyzed cyanations of aryl halides are readily enabled by visible light,in which Ni(Ⅱ)species are transiently oxidized to Ni(Ⅲ)species,thereby facilitating subsequent cyanide transfer and RE.Using this dual catalysis strategy,we cyanated aryl and alkenyl halides at room temperature in a highly benign manner(30 examples,53-93% yield)by avoiding the use of air-sensitive ligands,Ni(0)precursors,and hypertoxic cyanation reagents,while also limiting excess metal waste.Computational studies were also used to help understand the present transformation.

Alternating current electrolysis:A photoredox catalysis mimic and beyond

Alternating current electrolysis(ACE)is an emerging powerful synthetic tool,which principally resembles photoredox catalysis strategies.Its periodically alternating polarity feature allows oxidation and reduction processes to take place on the same electrode surface in a well-controlled manner via the fine-tuning of current frequency along with other reaction parameters.Therefore,many challenging transformations in typical direct electrolysis,including constant current electrolysis or constant potential electrolysis,could be achieved via ACE.The recent advances in the organic synthesis using this emerging technology and its advantages over direct electrolysis are highlighted.

Benign perfluoroalkylation of uracils and uracil nucleosides via visible light-induced photoredox catalysis

In this work, an efficient and facile method for the preparation of 5-perfluoroalkylation uracils and uracil nucleosides through visible-light-mediated reaction has been developed. The reaction processes in high efficiency under mild reaction conditions and show broad substrate scope by employing commercial available perfluoroalkyl sources, thus demonstrates high potent application in life and medicinal science.

Synergistic Brønsted Base/Photoredox-Catalyzed Three-Component Coupling with Malonates to Synthesize δ-Hydroxy Esters and δ-Keto Esters

Multicomponent alkene 1,2-dicarbofunctionalizations(DCFs)have emerged as a powerful strategy to rapidly incorporate both two carbon subunits across one C-C double bond in one step for enhancing molecular complexity and diversity.To the best of our knowledge,there is only one report on photoredox-catalyzed three-component DCFs with malonates through the radical−radical cross-coupling,while photoredox-catalyzed radical-polar crossover(RPC)-type DCFs with malonates were still rare.Herein,we describe a redox-neutral RPC-type 1,2-dialkylation of styrenes with malonates and aldehydes through the synergistic Brønsted base/photoredox catalysis system.This transition-metal-free strategy provides an efficient and clean approach to a broad variety ofδ-hydroxy esters and also features exceptionally mild conditions,wide compatibility of substrate scope and functional groups,and high atomic economy.Moreover,three-component 1,2-alkylacylation from the same starting materials was achieved in one-pot manner through such RPC-type coupling and subsequent two-electron oxidation process,providing a set ofδ-keto esters of interest in pharmaceutical research.

Metallaphotoredox-Catalyzed Three-Component Couplings for Practical Synthesis of Ureas and Carbamates

Ureas are widely used in drugs,materials and catalysts because of their diamide structure,which can form strong hydrogen bonds.Therefore,it is of great scientific significance to develop efficient and green methods for the synthesis of urea compounds,especially unsymmetrical ureas.Here,we have disclosed novel and highly efficient three-component coupling reactions of organic halides,sodium cyanate and amines enabled by nickel/photoredox dual catalysis for the preparation of unsymmetrical ureas.The reaction features simple and safe operations,broad substrate scopes,and product diversities.It allows the facile synthesis of N-aryl/vinyl ureas from readily available,user-friendly feedstocks under mild conditions(27 examples,36%—98%yields).In addition,this method is further derived to alcohols as nucleophiles to synthesize a series of carbamates(15 examples,40%—95%yields).The mechanism experiment shows that the isocyanate produced by the coupling of halide and sodium cyanate may be the key intermediate in this reaction.

Photoredox-catalyzed C-glycosylation of peptides with glycosyl bromides

Glycosyl radicals,produced under mild photoredox conditions,show unique utility in the preparation of C-linked glycoconjugates.We herein report the construction of C-glycosidic bonds on α,β-dehydroalanine(DHA)of peptides with easily available glycosyl bromides as glycosyl radical precursors under highly anomeric control,leading to C-glycosylation modifications of peptides.This method not only has outstanding functional group compatibility,but also is feasible in near-physiological conditions(pH~7 and temperature T≤37℃ in aqueous media).

Photoredox catalytic alkylarylation of alkynes with arylsulfonylacetate as bifunctional reagent

Difunctionalization of alkynes represents a powerful and straightforward approach to the synthesis of complex molecules.However,the radical difunctionalization of alkynes mediated by bifunctional reagents remains challenging and underexplored,despite significant progress having been made in alkene difunctionalization.Here,we report a novel arylsulfonylacetate skeleton in which aryl rings are attached to acetates through SO_(2),serving as a powerful bifunctional reagent for the alkylarylation of alkynes via vinyl-radical intermediate under photoredox conditions.This modular bifunctional reagent enables the simultaneous incorporation of a wide range of functional groups,including(hetero)aryl ring and alkyl carboxylate into alkynes,resulting in synthetically valuable all-carbon tetrasubstituted alkene derivatives.This transformation is distinguished by its redox-neutral nature,readily accessible starting materials,compatibility with diverse functional groups and its capacity to facilitate convergent synthesis.The utility of this approach was further demonstrated by the late-stage functionalization of complex molecules and the preparation of fluorescent molecules and anti-cancer drugs.

Annulation Cascades of Cyclosulfonium Salts and Alkenes towards Sulfur-Containing N-Heterocycles by Visible Light/Copper Catalysis

Although,great achievements have been made in the synthesis of heterocycles using radical addition/cyclization strategy,developing versatile alkyl radical precursors,especially the non-stabilized long chain alkyl radicals for this strategy still remains a huge challenge.Herein,we report an efficient annulation cascade reaction between cyclosulfonium salts and alkenes for the synthesis of sulfur-containing N-heterocycles by visible light/copper catalysis under mild conditions.The C—S bond cleavage/radical cascade reaction delivers a variety of corresponding N-heterocycles containing aryl alkyl thioether motifs with good functional group tolerance.Significantly,the current system could be used for the late-stage functionalization of complex bioactive molecules.

Visible-light photoredox-catalyzed carboxylation of aryl epoxides with CO_(2)

Herein, we report the first visible-light photoredox-catalyzed carboxylation of aryl epoxides with CO_(2)to synthesize hydroxy acid derivatives. A variety of valuable β-, γ-, δ-, ε–hydroxy acid derivatives are obtained in moderate to high yields under mild conditions. This protocol shows noteworthy functionalgroup compatibility, high chemo-and regioselectivities under transition-metal-free conditions with an inexpensive organo-dye as photosensitizer. Mechanistic studies indicate that the benzylic carbanion is generated as an intermediate via the sequential single electron transfer(SSET) process.

Photoredox Synthesis of Thio-Functionalized Cyclic Ethers Using N-Sulfenyl Phthalimides as a Thiyl-Radical Precursor

Comprehensive Summary A visible-light mediated exclusively regioselective synthesis of 2,2-disubstituted thio-functionalized tetrahydrofurans,tetrahydro-pyrans and oxepanes has been described through an operationally simple and mild photoredox protocol.Thiyl radical generated from N-phenylsulfenyl phthalimide by photoredox catalysis was proven to be the key reactive intermediate in this reaction.

Metal-Free Photocatalytic[4+2]Annulation of Acrylamides with 2-Benzyl-2-bromocarbonyls to Assemble Tetralin-1-carboxamides

Tetralin-1-carboxamides are frequently incorporated in myriad medicinally important molecules.However,their existing synthetic routes not only suffer from some drawbacks such as tedious procedures,harsh reaction conditions,narrow substrate scope,low yields,and environmental problems,but are also based upon the elaboration of uneasily available non-linear tetralin derivatives.Herein,we describe a metal-and additive-free visible light-induced[4+2]annulation of two simple linear starting materials,namely acrylamides and 2-benzyl-2-bromocarbonyls,through a cascade C(sp^(3))-Br/C(sp^(2))-H bond cleavage,double C-C bond formation,and aromatization sequence.The developed protocol provides a convenient,efficient,and green approach to a variety of tetralin-1-carboxamide derivatives with good functional group compatibility.Importantly,the resulting products could also undergo the Licl-mediated mono-decarboxylative cyclization process to further furnish the architecturally novel bridged polycyclic imides with excellentcis-diastereoselectivities.

Visible-Light-Driven Four-Component Radical Relay Aminocarbonylation of Unactivated Alkenes

Catalytic four-component radical carbonylation of unactivated alkenes has recently been recognized as a robust protocol for rapid construction of various structurally diverse carbonyl compounds.Given the significance of fluorine-containing groups,this reaction class has been extensively applied to assembly of a variety of perfluoroalkyl carboxylic acid derivatives by transition metal catalysis.Herein,we report a visible-light-driven radical relay 1,2-perfluoroalkylation aminocarbonylation of unactivated alkenes using CO gas as carbonyl source and 4CzIPN as organic photocatalyst.A wide range of alkenes and amines were well tolerated,providing the valuableβ-perfluoroalkylated amides with generally good yields and high chemoselectivity.

Recent advances in visible-light photoredox-catalyzed nitrogen radical cyclization

Visible-light photoredox catalysis is a powerful and attractive strategy for organic molecule activation and new reaction design owing to its environmental-friendly characteristics and unique catalytic mechanisms,and has found wide applications in organic synthesis.This catalytic strategy enables controllable generation of diverse nitrogen-centered radicals(NCRs)under mild conditions,providing access to construction of diverse nitrogencontaining compounds.In this review,we critically illustrate the recent advances in the field of visible-light photoredox-catalyzed cyclization of nitrogen-centered radicals,based on the different radical precursors and activation modes.Wherever possible,particular emphasis is also put on working models and synthetic applications.

Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

A photoredox/palladium-cocatalyzed enantioselective alkylation of racemic secondary carbonates with 4-alkyl-1,4-dihydropyridines under visible light irradiation has been developed. The present study provides a method for the preparation of optically active diarylalkanes from racemic diarylmethyl carbonates by a dynamic kinetic asymmetric transformation(DYKAT).This photoredox/palladium dual catalysis strategy expands the scope of the asymmetric Pd-catalyzed benzylic substitution reaction and serves as its potential alternative and complement.