Photoinduced Copper-Catalyzed Site-Selective C(sp2)–C(sp) Cross-Coupling via Aryl Sulfonium Salts

Photoredox Ring Opening 1,2-Alkylarylation of Alkenes with Sulfonium Salts Toward Thioether-Substituted Oxindoles

A novel strategy for the difunctionalization of electron-deficient alkenes with aryl sulfonium salts to access remote sulfur-containing oxindole derivatives by using in situ-formed copper(I)-based complexes as a photoredox catalyst is presented. This method enables the generation of the C(sp3)-centered radicals through site selective cleavage of the C-S bond of aryl sulfonium salts under mild conditions. Moreover, the oxidation reactions of desired products provide a new strategy for the preparation of sulfoxide or sulfone-containing compounds. Importantly, this approach can be easily applied to late-stage modification of pharmaceuticals molecules.

Silver-Promoted Rapid Synthesis of 3-Arylindan-1-ones: Microwave-Assisted Reductive Coupling of N-Tosylhydrazone and Boronic Acids

An efficient and straightforward one-pot tandem synthesis of 3-arylindan-1-ones was consummated through silver nitrate-promoted C-C coupling of simple indane-1,3-dione with arylboronic acid via 1,3-indanedione monotosylhydrazone under microwave conditions. The resulting series of 3-arylindan-1-ones exhibited impressive yields, surpassing those achievable with traditional methods and requiring a shorter time frame. This innovative approach significantly accelerated the synthesis of biologically active compounds such as (+)-indatraline (Lu 19-005) and several other industrially relevant substances.

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Palladium(II)-Catalyzed Heck Coupling: Direct Stereoselective Synthesis of C-Aryl Glycosides from Nonactivated Glycals and Thianthrenium Salts

Here, we report an efficient Pd(II)-catalyzed Heck coupling reaction utilizing modular and readily available thianthrenium salts. The tunability and ease of thianthrenium salts facilitated the integration of glycals with drugs, natural products, and peptides. This method allows the incorporation of diverse glycals into structurally varied aglycon components without directing groups or prefunctionalization and provides a practical method for synthesizing C-aryl glycosides, offering a new avenue for the production of complex glycosides with potential applications.

Site-selective carbonylation of arenes via C(sp2)-H thianthrenation: direct access to 1,2-diarylethanones

Herein, a new reaction for the site-selective carbonylation of arenes via C(sp²)-H thianthrenation under mild conditions has been developed. With low loadings of palladium catalysts, various desired 1,2-diarylethanones are produced in good yields. This strategy also enables the late-stage modification of complex molecules, which was previously challenging with similar carbonylative Negishi-type reactions.

Photocatalytic Late-Stage C-H Functionalization

The emergence of modern photocatalysis, characterized by mildness and selectivity, has significantly spurred innovative late-stage C-H functionalization approaches that make use of low energy photons as a controllable energy source. Compared to traditional late-stage functionalization strategies, photocatalysis paves the way toward complementary and/or previously unattainable regio- and chemoselectivities. Merging the compelling benefits of photocatalysis with the late-stage functionalization workflow offers a potentially unmatched arsenal to tackle drug development campaigns and beyond. This Review highlights the photocatalytic late-stage C-H functionalization strategies of small-molecule drugs, agrochemicals, and natural products, classified according to the targeted C-H bond and the newly formed one. Emphasis is devoted to identifying, describing, and comparing the main mechanistic scenarios. The Review draws a critical comparison between established ionic chemistry and photocatalyzed radical-based manifolds. The Review aims to establish the current state-of-the-art and illustrate the key unsolved challenges to be addressed in the future. The authors aim to introduce the general readership to the main approaches toward photocatalytic late-stage C-H functionalization, and specialist practitioners to the critical evaluation of the current methodologies, potential for improvement, and future uncharted directions.

Organothianthrenium salts: synthesis and utilization

Organothianthrenium salts are a class of compounds containing a positively charged sulfur atom and a neutral sulfur atom. Over the past years, organothianthrenium salts have been emerging as attractive precursors for a myriad of transformations to forge new C-C and C-X bonds due to their unique structural characteristics and chemical behaviors. The use of the thianthrenation strategy selectively transforms C-H, C-O, and other chemical bonds into organothianthrenium salts in a predictable manner, providing a straightforward alternative for regioselective functionalizations for arenes, alkenes, alkanes, alcohols, amines and so on through diverse reaction mechanisms under mild conditions. In this review, the preparation of different organothianthrenium salts is summarized, including aryl, alkenyl and alkyl thianthrenium salts. Moreover, the utilization of organothianthrenium salts in different catalytic processes and their synthetic potentials are also discussed.

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Copper-catalyzed deacetonative Sonogashira coupling

A convenient Pd- and phosphine-free protocol for assembling internal alkynes from tertiary propargyl alcohols and (het)aryl halides has been developed. The proposed tandem approach includes the base-promoted retro-Favorskii fragmentation followed by Cu-catalyzed C(sp)-C(sp²) cross-coupling. The use of inexpensive reagents (e.g. a catalyst, additives, a base, and a solvent) and good functional group tolerance make the procedure practical and cost-effective. The synthetic utility of the method was demonstrated by a smooth alkynylation of vinyl iodides derived from natural steroidal hormones.

Recent Advances in Thianthrenation/Phenoxathiination Enabled Site-Selective Functionalization of Arenes

Site-selective functionalization of simple arenes remains a paramount challenge due to the similarity of multiple C–H bonds in the same molecule with similar steric environment and electronic properties. Recently, the site-selective thianthrenation/phenoxathiination of arenes has become an attractive solution to reach this challenging goal and it has been applied in the late-stage functionalization of various bioactive molecules. This short review aims to summarize recent advances in the site-selective C–H functionalization of arenes via aryl thianthrenium salts, as well as mechanistic insights in the remarkable site-selectivity obtained in thianthrenation step.

1 Introduction

2 Site-Selective Thianthrenation of Arenes and Mechanistic Insight

3 Thianthrenation-Enabled Site-Selective Functionalization of Arenes

3.1 Thianthrenation-Enabled C(sp 2)–C Bond Formation Reaction

3.2 Thianthrenation-Enabled C(sp 2)–X Bond Formation Reaction

4 Conclusion and Outlook

Visible-light-catalyzed C-H arylation of (hetero)arenes via arylselenonium salts

A novel photo-induced C-H arylation of (hetero)arenes has been developed. Aryl selenonium salts as an aryl source led to the arylation of aromatic (hetero)cyclic compounds via C-Se bond activation under blue LED irradiation. The method simply utilizes the safe and clean energy source and yields a range of site-selective biphenyl or bi-heterocyclic products in medium to good yields. Furthermore, the borylation and Sonogashira coupling of aryl selenonium salts proceed in good yields as well. From the results, it is shown that selenonium salts are more reactive than sulfonium salts.

Photoredox-Catalyzed α-Sulfonylation of Ketones from Sulfur Dioxide and Thianthrenium Salts

A photoredox-catalyzed sulfonylation of silyl enol ethers with DABCO·(SO₂)₂ and thianthrenium salts is achieved, providing diverse β-keto sulfones in moderate to good yields. This protocol features easily accessible starting materials and good functional group compatibility, enabling the introduction of various functionalized sulfonyl groups into ketones. Furthermore, as one of the important industrial raw materials, methanol can be employed as the methyl source to prepare α-methylsulfonated ketones through a methyl thianthrenium intermediate for the first time.

Organometallic catalysis under visible light activation: benefits and preliminary rationales

Organometallic catalysis under visible light activation is an emerging field. Activation by photosensitization or by direct light absorption of organometallic complexes can facilitate or trigger elementary steps in a catalytic cycle such as pre-catalyst reduction, oxidative addition, transmetalation and reductive elimination, as well as the ability of generating radical intermediates, widening the structural diversity offered by classical couplings. This perspective aims to highlight key examples of these light-induced or enhanced processes, with an emphasis on the underlying mechanisms involved.

TEMPO-mediated late stage photochemical hydroxylation of biaryl sulfonium salts

The late stage photochemical hydroxylation of biaryl sulfonium salts was enabled with a TEMPO derivative as a simple oxygen source, in metal free conditions. The scope and mechanism of this exceptionally simple synthetic method, which constructs important arylated phenols from aromatic C-H bonds, are herein discussed.

Photoredox-catalyzed reaction of thianthrenium salts, sulfur dioxide and hydrazines

A photoredox-catalyzed reaction of thianthrenium salts, hydrazines and DABCO·(SO2)2 is accomplished, providing diverse arenesulfonohydrazides in moderate to good yields under mild reaction conditions.

A desulphurization strategy for Sonogashira couplings by visible light/copper catalysis

We have developed a new copper-based photocatalyst, [(binap)(tpy)Cu]Cl, and applied it in the visible-light promoted Sonogashira coupling reactions.

Recent Advances in Visible-Light-Promoted Copper Catalysis in Organic Reactions

In recent years, visible-light-mediated copper photocatalysis has emerged as an attractive strategy for the diverse construction of basic bonds in an ecologically benign and cost-effective fashion. The intense activity in these areas has been stimulated by the distinctive properties of copper photocatalysts and has led to the rapid development and expansion of their applications. In this review, we focus on a series of significant achievements in the use of copper complexes as standalone photocatalysts in organic reactions to exhibit their high flexibility and potential in synthetic chemistry.

1 Introduction

2 Redox Coupling Reactions

2.1 Carbon–Nitrogen Redox Coupling Reactions

2.2 Carbon–Carbon Redox Coupling Reactions

3 Oxidative Coupling Reactions

4 Difunctionalization of Olefins

5 C–H Bond Functionalization

6 Radical Alkylation of Imines

7 Conclusions and Outlook

Construction of α-Amino Azines via Thianthrenation-Enabled Photocatalyzed Hydroarylation of Azine-Substituted Enamides with Arenes

α-Amino azines are widely found in pharmaceuticals and ligands. Herein, we report a practical method for accessing this class of compounds via photocatalyzed hydroarylation of azine-substituted enamides with the in situ-generated aryl thianthrenium salts as the radical precursor. This reaction features a broad substrate scope, good functional group tolerance, and mild conditions and is suitable for the late-stage installation of α-amino azines in complex structures.

Transition Metal-Free C-H Thiolation via Sulfonium Salts Using β-Sulfinylesters as the Sulfur Source

We disclose a direct C(sp)-, C(sp²)-, and C(sp³)-H thiolation reaction using β-sulfinylesters as the versatile sulfur source. The key step of this protocol is chemoselective C-S bond cleavage of the sulfonium salts that are formed in situ from the corresponding alkenes, alkynes, and 1,3-dicarboxyl compounds with β-sulfinylesters. The successful capture of the acrylate byproduct supports a retro-Michael reaction mechanism.

Enabling the Use of Alkyl Thianthrenium Salts in Cross-Coupling Reactions by Copper Catalysis

Alkyl groups are one of the most widely used groups in organic synthesis. Here, a a series of thianthrenium salts have been synthesized that act as reliable alkylation reagents and readily engage in copper-catalyzed Sonogashira reactions to build C(sp³ )-C(sp) bonds under mild photochemical conditions. Diverse alkyl thianthrenium salts, including methyl and disubstituted thianthrenium salts, are employed with great functional breadth, since sensitive Cl, Br, and I atoms, which are poorly tolerated in conventional approaches, are compatible. The generality of the developed alkyl reagents has also been demonstrated in copper-catalyzed Kumada reactions.

Late-Stage Heteroarylation of Hetero(aryl)sulfonium Salts Activated by α-Amino Alkyl Radicals

We report a late‐stage heteroarylation of aryl sulfonium salts through activation with α‐amino alkyl radicals in a mechanistically distinct approach from previously reported halogen‐atom transfer (XAT). The new mode of activation of aryl sulfonium salts proceeds in the absence of light and photoredox catalysts, engaging a wide range of hetarenes. Furthermore, we demonstrate the applicability of this methodology in synthetically useful cross‐coupling transformations.

Trifluoromethyl Thianthrenium Triflate: A Readily Available Trifluoromethylating Reagent with Formal CF3+, CF3•, and CF3- Reactivity

Here we report the synthesis and application of trifluoromethyl thianthrenium triflate (TT-CF₃⁺OTf^–) as a novel trifluoromethylating reagent, which is conveniently accessible in a single step from thianthrene and triflic anhydride. We demonstrate the use of TT-CF₃⁺OTf^– in electrophilic, radical, and nucleophilic trifluoromethylation reactions.

SOMOphilic alkynylation using acetylenic sulfones as functional reagents

Recent advancements in SOMOphilic alkynylation reactions by using acetylenic sulfones as functional reagents are summarized.