Photocatalytic dual decarboxylative alkenylation mediated by triphenylphosphine and sodium iodide

Iron-Catalyzed Csp2-Csp3 Cross-Coupling via Double Decarboxylation: One Step Synthesis of Remote Polar Alkenes

Herein, we report an efficient photoinduced iron-catalyzed strategy for cross-couplings of alkyl carboxylic and acrylic acids, which provides a powerful tool for the synthesis of a variety of alkenes with polar functional groups. This novel synthetic methodology can also be applied to the preparation of ketones by using α-keto acids. Mechanistic experiments revealed preliminary mechanistic details. Diverse functionalization could be achieved, which may help streamline the synthesis of complex analogues for drug discovery.

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

Photoredox catalysis plays a crucial role in contemporary synthetic organic chemistry. Since the groundbreaking work of Shang and Fu on photocatalytic decarboxylative alkylations in 2019, a wide range of organic transformations, such as alkylation, alkenylation, cyclization, amination, iodination, and monofluoromethylation, have been progressively achieved using a combination of iodide and PPh3. In this review, we primarily focus on summarizing the recent advancements in inexpensive and readily available iodide/phosphine-mediated photoredox radical transformations.

Visible-light-mediated synthesis of oxime esters via multicomponent reactions of aldehydes, aryl amines, and N-hydroxyphthalimide esters

Oxime esters are useful scaffolds in many organic chemistry transformations. Herein, a novel visible-light-mediated three-component reaction for synthesis of oxime esters is reported. Aldehydes, aniline, and N-hydroxyphthalimide (NHPI) esters were used as substrates in this three-component reaction, and eosin Y was used as a crucial photocatalyst for the reaction. Wide ranges of aldehydes and NHPI esters were well tolerated in this reaction method, generating various oxime esters with high efficiency under mild reaction conditions. This visible-light-mediated methodology will be a promising approach to synthesize useful oxime esters in a single step.

A Chemoselective Polarity-Mismatched Photocatalytic C(sp3 )-C(sp2 ) Cross-Coupling Enabled by Synergistic Boron Activation

We report the development of a C(sp3 )-C(sp2 ) coupling reaction using styrene boronic acids and redox-active esters under photoredox catalysis. The reaction proceeds through an unusual polarity-mismatched radical addition mechanism that is orthogonal to established processes. Synergistic activation of the radical precursor and organoboron are critical mechanistic events. Activation of an N-hydroxyphthalimide (NHPI) ester by coordination to boron enables electron transfer, with decomposition leading to a nucleofuge rebound, activating the organoboron to radical addition. The unique mechanism enables chemoselective coupling of styrene boronic acids in the presence of other alkene radical acceptors. The scope and limitations of the reaction, and a detailed mechanistic investigation are presented.

Visible-Light-Promoted Decarboxylative Alkylation/Cyclization of Vinylcycloalkanes

An efficient strategy for visible-light-promoted decarboxylative alkylation of vinylcyclopropanes with alkyl N-(acyloxy)phthalimide esters through the dual C-C bond and single N-O bond cleavage, employing triphenylphosphine and lithium iodide as the photoredox system to synthesize 2-alkylated 3,4-dihydronaphthalenes, has been established. This alkylation/cyclization involves a radical process and undergoes a sequence of N-(acyloxy)phthalimide ester single-electron reduction, N-O bond cleavage, decarboxylative, alkyl radical addition, C-C bond cleavage, and intramolecular cyclization. Moreover, using the photocatalyst Na₂-Eosin Y instead of triphenylphosphine and lithium iodide, the vinyl transfer products are acquired when vinylcyclobutanes or vinylcyclopentanes are utilized as alkyl radical receptors.

NaI/PPh3-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

A practical NaI/PPh3-catalyzed decarboxylative radical cascade cyclization of N-arylacrylamides with redox-active esters is described, which is mediated by visible light irradiation. A wide range of substrates bearing different substituents and derived from ubiquitous carboxylic acids, including α-amino acids, were synthesized and examined under this very mild, efficient, and cost effective transition-metal-free synthetic method. These afforded various functionalized oxindoles featuring a C3 quaternary stereogenic center. Mechanistic experiments suggest a radical mechanism.

Visible-Light-Induced Decarboxylative Alkylation/Ring Opening and Esterification of Vinylcyclopropanes

A visible-light-induced four-component reaction of vinylcyclopropanes, N-(acyloxy)phthalimide esters, N,N-dimethylformamide (DMF), and H₂O through an oxidative ring opening of cyclopropane is presented. This procedure provides a new and effective way to construct formate esters. DMF is employed as both a solvent and the source of CHO. This difunctionalization of vinylcyclopropanes shows good functional group tolerance under room temperature. A radical pathway is involved, and carbonyl oxygen of ester originated from water in this transformation.

Copper-Mediated Cyclization of o-Hydroxyaryl Enaminones with 3-Indoleacetic Acids toward the Synthesis of 3-Indolmethyl-Chromones

Here, we describe a copper-mediated tandem decarboxylative coupling/annulation protocol of o-hydroxyaryl enaminones with 3-indoleacetic acids. A series of 3-indolmethyl-chromones were afforded in up to 97% yield. A one-pot method for 3-indolmethyl-chromones from o-hydroxy acetophenones, N, N-dimethylformamide dimethyl acetal, and 3-indoleacetic acids was also developed. Derivatization of the products was conducted to provide various indolmethyl-substituted pyrimidines. Moreover, a biological evaluation revealed that some compounds had anti-influenza viral activities.

Visible light-promoted, photocatalyst-free decarboxylative alkylations of 2H-indazoles via electron donor-acceptor-complex activation

A transition-metal-free and traditional dye-free visible light-driven directly alkylation of 2-aryl-2H-indazoles was developed in the catalytic of an electron donor-acceptor (EDA) complex among alkyl N-hydroxyphthalimide (NHPI) esters, triphenylphosphine (PPh3), and...

Visible-light-mediated decarboxylative alkylation of 2-pyridone derivatives via a C3-selective C-H functionalization

A direct C-H functionalization approach to access C3-alkylated 2-pyridone derivatives is reported. This study utilizes N-hydroxyphthalimide (NHPI) esters of various carboxylic acids as sources of alkyl radicals by reductive cleavage under photocatalytic reaction conditions. The carbon-carbon bond formation occurred site-selectively at C3 of 2-pyridone to give the desired products in moderate to good yields. This method enables a faster access to C3-alkylated pyridone compounds which can be applied to the synthesis of small molecule drugs.

Photocatalytic Decarboxylative [3 + 2] and [4 + 2] Annulation of Enynals and γ,σ-Unsaturated N-(Acyloxy)phthalimides by NaI/PPh3 Catalysis

A practical and eco-friendly strategy for the radical-mediated decarboxylative [3 + 2] and [4 + 2] annulation of enynals and γ,σ-unsaturated N-(acyloxy)phthalimides through the photoactivation of an electron donor-acceptor (EDA) complex has been developed. A wide range of primary, secondary, and tertiary alkyl N-hydroxyphthalimide (NHP) esters can be used as suitable substrates for the synthesis of fused ketones without any transition-metal catalysts or oxidants. This protocol features a broad substrate scope, excellent selectivity, and clean reaction conditions.

Progress and Prospect of Organic Electrocatalysts in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition-metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li-S batteries and discusses the structure-activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li-S batteries are also discussed.

Dual Nickel/Ruthenium Strategy for Photoinduced Decarboxylative Cross-Coupling of α,β-Unsaturated Carboxylic Acids with Cycloketone Oxime Esters

Herein, a dual nickel/ruthenium strategy is developed for photoinduced decarboxylative cross-coupling between α,β-unsaturated carboxylic acids and cycloketone oxime esters. The reaction mechanism is distinct from previous photoinduced decarboxylation of α,β-unsaturated carboxylic acids. This reaction might proceed through a nickelacyclopropane intermediate. The C(sp²)-C(sp³) bond constructed by the aforementioned reaction provides an efficient approach to obtaining various cyanoalkyl alkenes, which are synthetically valuable organic skeletons in organic and medicinal chemistry, under mild reaction conditions. The protocol tolerates many critical functional groups and provides a route for the modification of complex organic molecules.

Photocatalytic decarboxylative alkylation of silyl enol ether and enamide with N-(acyloxy)phthalimide using ammonium iodide

Under visible light, a catalytic amount of ammonium iodide promotes the decarboxylative alkylation of silyl enol ether and enamide with aliphatic N-(acyloxy)phthalimide through the photoactivation of a transiently assembled chromophore.

Visible-light-induced iodine-anion-catalyzed decarboxylative/deaminative C–H alkylation of enamides

An efficient method for photo-induced iodine-anion-catalyzed C–H alkylation of enamides has been developed. Redox-active esters and Katritzky salts of amino acids are amenable, successfully delivering various functionalized enamides.

Copper-catalyzed oxidative decarboxylative alkylation of cinnamic acids with 4-alkyl-1,4-dihydropyridines

We have developed a new oxidative decarboxylation of cinnamic acids with 4-alkyl-1,4-dihydropyridines to construct C(sp3)-C(sp2) bonds in the presence of copper catalyst and dicumyl peroxide (DCP). A variety of internal alkenes have been obtained with mild conditions, broad substrate scope and excellent functional group tolerance. This method has significant potential for application by using inexpensive and stable cinnamic acids instead of alkenyl halides and nitro-olefins.

Metal-free decarboxylative annulation of N-arylacrylamides with vinyl acids to synthesize benzo[b]azepin-2-ones

An efficient oxidative decarbonylative (3 + 2)/(5 + 2) annulation of N-arylacrylamides with vinyl acids for the synthesis of diverse seven-membered N-heterocycles under metal-free conditions has been developed.