Photoinduced Copper‐Catalyzed Regioselective Synthesis of Indoles: Three‐Component Coupling of Arylamines, Terminal Alkynes, and Quinones

Copper (I) Chloride-Catalyzed Photoredox Synthesis of Multifunctionalized Compounds at Room Temperature and Their Antifungal Activities

A simple visible-light-induced CuCl-catalyzed synthesis was developed for highly functionalized carbon-centered compounds (α-alk/aryloxy-α-diaryl/alkylaryl-acetaldehydes/ketones) at room temperature using benzoquinone, alkyl/aryl alcohol, and alkyl/aryl terminal/internal alkynes. Late-stage functionalized compounds show good antifungal activities, especially against Candida krusei fungal strain, in in vitro experiments (the Broth microdilution method). Moreover, toxicity tests (zebrafish egg model experiments) indicated that these compounds had negligible cytotoxicity. The green chemistry metrics (E-factor value is 7.3) and eco-scale (eco-scale value is 58.8) evaluations show that the method is simple, mild, highly efficient, eco-friendly, and environmentally feasible.

Synthesis of Ketonylated Carbocycles via Excited-State Copper-Catalyzed Radical Carbo-Aroylation of Unactivated Alkenes

Carbocycles are core skeletons in natural and synthetic organic compounds possessing a wide diversity of important biological activities. Herein, we report the development of an excited-state copper-catalyzed radical carbo-aroylation of unactivated alkenes to synthesize ketonylated tetralins, di- and tetrahydrophenanthrenes, and cyclopentane derivatives. The reaction is operationally simple and features mild reaction conditions that tolerate a broad range of functional groups. Preliminary mechanistic studies suggest a reaction pathway beginning with photoexcitation of [CuI-BINAP]2 and followed by a single electron transfer (SET), radical aroylation of unactivated alkenes, radical cyclization, and re-aromatization, affording the desired ketonylated carbocycles.

Visible-Light-Induced Oxidative α-keto-Dichlorination of Arylalkynes by CuCl2 at Room Temperature

A visible light-induced oxidative α-keto-dichlorination of terminal and internal aryl alkynes was developed to form dichloroacetophenones (DCAPs) and dichlorophenyl-acetophenones (DCPAPs), respectively, by using CuCl₂ as a photoredox catalyst in the presence of air at room temperature (without using any exogenous photocatalyst). Here, photoexcited CuCl₂ underwent ligand-to-metal charge transfer to generate a Cl radical, which readily added to the alkynes to form DCAPs or DCPAPs in the presence of O₂ . This α-keto-dichlorination reaction is a green and mild protocol as it produced water as the only by-product. Moreover, the evaluation of green chemistry metrics indicated that the E-factor (mass of wastes/mass of products) of the current α-keto-chlorination method is around 10.1 times lower than that of a literature-reported photochemical method. The Eco Scale value (score 55, which on a scale of 0-100 indicates an acceptable synthesis) signifies that this process is simple, highly efficient, eco-friendly, and cost-effective.

Excited-State Copper Catalysis for the Synthesis of Heterocycles

Heterocycles are one of the largest groups of organic moieties with significant medicinal, chemical, and industrial applications. Herein, we report the discovery and development of visible-light-induced, synergistic excited-state copper catalysis using a combination of Cu(IPr)I as a catalyst and rac-BINAP as a ligand, which produces more than 10 distinct classes of heterocycles. The reaction tolerates a broad array of functional groups and complex molecular scaffolds, including derivatives of peptides, natural products, and marketed drugs. Preliminary mechanistic investigation suggests in situ generations of [Cu(BINAP)₂ ]⁺ and [Cu(IPr)₂ ]⁺ catalysts that work cooperatively under visible-light irradiation to facilitate catalytic carbo-aroylation of unactivated alkenes, affording a wide range of useful heterocycles.

Visible-light-mediated copper photocatalysis for organic syntheses

Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C-H functionalization that have been reported over the past 5 years, are included.

Recent Advances on Photoinduced Cascade Strategies for the Synthesis of N-Heterocycles

Over the last decade, visible-light photocatalysis has proved to be a powerful tool for the construction of N-heterocyclic frameworks, important constituents of natural products, insecticides, pharmacologically relevant therapeutic agents and catalysts. This account highlights recent developments and established methods towards the photocatalytic cascades for preparation of different classes of N-heterocycles, giving emphasis on our contribution to the field.

meta-Selective C-H Activation of Arenes at Room Temperature Using Visible Light: Dual-Function Ruthenium Catalysis

Ruthenium-catalyzed meta-C-H activation of arenes at room temperature is reported to proceed under blue-light irradiation. A variety of heteroarenes are compatible with this photochemical process, which leads to the corresponding meta C-C coupling products in good to very good yields. Initial mechanistic studies suggest a single-electron transfer process occurs between a photoexcited Ru^II -cyclometalated complex and alkyl halides, enabling meta-C-H functionalization reaction via carbon-centered radicals.

Photocatalysis in organic and polymer synthesis

This review, with over 600 references, summarizes the recent applications of photoredox catalysis for organic transformation and polymer synthesis. Photoredox catalysts are metallo- or organo-compounds capable of absorbing visible light, resulting in an excited state species. This excited state species can donate or accept an electron from other substrates to mediate redox reactions at ambient temperature with high atom efficiency. These catalysts have been successfully implemented for the discovery of novel organic reactions and synthesis of added-value chemicals with an excellent control of selectivity and stereo-regularity. More recently, such catalysts have been implemented by polymer chemists to post-modify polymers in high yields, as well as to effectively catalyze reversible deactivation radical polymerizations and living polymerizations. These catalysts create new approaches for advanced organic transformation and polymer synthesis. The objective of this review is to give an overview of this emerging field to organic and polymer chemists as well as materials scientists.

Photoredox Catalysis with Metal Complexes Made from Earth-Abundant Elements

Photoredox chemistry with metal complexes as sensitizers and catalysts frequently relies on precious elements such as ruthenium or iridium. Over the past 5 years, important progress towards the use of complexes made from earth-abundant elements in photoredox catalysis has been made. This review summarizes the advances made with photoactive Cr^III , Fe^II , Cu^I , Zn^II , Zr^IV , Mo⁰ , and U^VI complexes in the context of synthetic organic photoredox chemistry using visible light as an energy input. Mechanistic considerations are combined with discussions of reaction types and scopes. Perspectives for the future of the field are discussed against the background of recent significant developments of new photoactive metal complexes made from earth-abundant elements.

Electrochemical C-H/N-H Functionalization for the Synthesis of Highly Functionalized (Aza)indoles

Indoles and azaindoles are among the most important heterocycles because of their prevalence in nature and their broad utility in pharmaceutical industry. Reported herein is an unprecedented noble-metal- and oxidant-free electrochemical method for the coupling of (hetero)arylamines with tethered alkynes to synthesize highly functionalized indoles, as well as the more challenging azaindoles.

Photoinduced Copper-Catalyzed C-H Arylation at Room Temperature

Room-temperature azole C-H arylations were accomplished with inexpensive copper(I) compounds by means of photoinduced catalysis. The expedient copper catalysis set the stage for site-selective C-H arylations of non-aromatic oxazolines under mild reaction conditions, and provides step-economical access to the alkaloid natural products balsoxin and texamine.

Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.