Copper-Catalyzed Intermolecular Difunctionalization of Styrenes with Thiosulfonates and Arylboronic Acids via a Radical Relay Pathway

Iodine(III)-promoted oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent

A metal-free protocol for oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent has been developed using (diacetoxyiodo)benzene (PIDA) as an oxidant. This three-component strategy enables one-step construction of 3,4-disubstituted maleimides in good yields with high functional group tolerance. Both experimental and theoretical studies support the proposed radical reaction mechanism.

A General Platform for Visible Light Sulfonylation Reactions Enabled by Catalytic Triarylamine EDA Complexes

Catalytic electron donor-acceptor (EDA) complexes have recently emerged as a powerful and sustainable alternative to iridium- and ruthenium-based photoredox synthetic methods. Yet, these complexes remain underexplored and reliant on the use of meticulously designed acceptors that require previous installation. Herein, we report a novel EDA complex employing tris(4-methoxyphenyl) amine as a catalytic donor for the sulfonylation of alkenes using inexpensive and readily available sulfonyl chlorides. Applying this operationally simple, visible-light-mediated general platform, we report both the redox-neutral and net-reductive functionalization of more than 60 substrates, encompassing vinylic or allylic sulfonylation, hydrosulfonylation, and sulfamoylation of activated and unactivated alkenes and alkynes.

Visible-Light-Induced Regioselective Radical Oxo-Amination of Alkenes with O2 as the Oxygen Source

An efficient and novel visible-light-induced oxo-amination of terminal alkenes for the construction of α-amino ketones with easily accessible and green O2 as the oxygen source has been developed. The transformation possesses the advantages of operational simplicity, a broad substrate scope, high atom economy, and mild reaction conditions. The mechanistic studies reveal that an energy transfer process probably occurs in the initial stage, and the reaction proceeds via β-scission of the alkoxyl radical species.

Synthesis of α-Quaternary β-Lactams via Copper-Catalyzed Enantioconvergent Radical C(sp3 )-C(sp2 ) Cross-Coupling with Organoboronate Esters

The copper-catalyzed enantioconvergent radical C(sp³ )-C(sp² ) cross-coupling of tertiary α-bromo-β-lactams with organoboronate esters could provide the synthetically valuable α-quaternary β-lactams. The challenge arises mainly from the construction of sterically congested quaternary stereocenters between the tertiary alkyl radicals and chiral copper(II) species. Herein, we describe our success in achieving such transformations through the utilization of a copper/hemilabile N,N,N-ligand catalyst to forge the sterically congested chiral C(sp³ )-C(sp² ) bond via a single-electron reduction/transmetalation/bond formation catalytic cycle. The synthetic potential of this approach is shown in the straightforward conversion of the corresponding products into many valuable building blocks. We hope that the developed catalytic cycle would open up new vistas for more enantioconvergent cross-coupling reactions.

Protocol for chemo- and regioselective C(sp3)-H activation using a heterogeneous copper powder-catalyzed reaction

Here, we present a protocol for the synthesis of dibenzo[c,e]oxepin-5(7H)-ones starting from 2'-alkyl-[1,1'-biphenyl]-2-carboxylic acids. This technique uses two copper(0)-catalyzed benzylic C(sp³)-H activation strategies taking either di-tertbutyl peroxide or gaseous oxygen as an oxidant. We detail a photocatalytic thermal approach for copper powder-catalyzed reaction with oxygen. We also describe a procedure for catalyst recycling in both the strategies. The product has been successfully synthesized both in mmol and gram scale. For complete details on the use and execution of this protocol, please refer to Nandi et al. (2022).

The C(sp3)-H bond functionalization of thioethers with styrenes with insight into the mechanism

A metal-free inactive C(sp³)-H bond functionalization of thioethers with styrenes using TBHP as an initiator and DBU as a base has been developed. This transformation has broken through the low activity of thioethers and realized moderate yields. Herein extended experiments were conducted to confirm the radical relay process, reaction energy and intermediate transformations.

Chemo- and regioselective benzylic C(sp3)–H oxidation bridging the gap between hetero- and homogeneous copper catalysis

Selective C‒H functionalization in a pool of proximal C‒H bonds, predictably altering their innate reactivity is a daunting challenge. We disclose here, an expedient synthesis of privileged seven-membered lactones, dibenzo[c,e]oxepin-5(7H)-one through a highly chemoselective benzylic C(sp³)‒H activation. Remarkably, the formation of widely explored six-membered lactone via C(sp²)‒H activation is suppressed under the present conditions. The reaction proceeds smoothly on use of inexpensive metallic copper catalyst and di-tert-butyl peroxide (DTBP). Owing to the hazards of stoichiometric DTBP, further, we have developed a sustainable metallic copper/rose bengal dual catalytic system coupled with molecular oxygen replacing DTBP. A 1,5-aryl migration through Smiles rearrangement was realized from the corresponding diaryl ether substrates instead of expected eight-membered lactones. The present methodology is scalable, applied to the total synthesis of cytotoxic and neuroprotective natural product alterlactone. The catalyst is recyclable and the reaction can be performed in a copper bottle without any added catalyst.

•

Catalytic strategy for chemo- and regioselective benzylic C–H activation

•

Bulk copper catalysis merging with photocatalysis

•

Reusable copper catalyst

•

Reaction demonstrated in commercial copper bottle without external catalyst

The synthesis of anticancer sulfonated indolo[2,1-a]isoquinoline and benzimidazo[2,1-a]isoquinolin-6(5H)-ones derivatives via a free radical cascade pathway

A facile CuBr₂ induced radical relay addition/cyclization of activated alkenes with substituted-thiosulfonates has been achieved, leading to a broad range of sulfonated indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolin-6(5H)-ones in moderate to good yields. In particular, some compounds exhibit bioactivity against cancer cell lines. This protocol shows advantages of low-cost, base-free, simple operation, and broad functional group tolerance.

Copper-Catalyzed Aldehyde Exchanged Amidation

The synthesis of bioactive amides has been the pursuit of chemists. Herein secondary amides incorporated with an aldehyde group were first generated using aldehydes and secondary amines. Various (hetero)aryl aldehydes and even aliphatic aldehydes (>40 examples) were converted into the desired products in moderate to excellent yields (up to 89%). A plausible mechanism involving a Cu(I/II/III) catalytic cycle combined with radical rearrangement was proposed and confirmed with four key intermediates detected by high-resolution mass spectrometry.

Visible-Light-Induced Radical Cascade Reaction of 1-Allyl-2-ethynylbenzoimidazoles with Thiosulfonates to Assemble Thiosulfonylated Pyrrolo[1,2-a]benzimidazoles

A visible-light-induced radical domino reaction of 1-allyl-2-ethynylbenzoimidazoles with thiosulfonates was developed, which generated the thiosulfonylated pyrrolo[1,2-a]benzimidazoles in moderate to good yields. This reaction proceeded under transition-metal-free conditions with good functional group tolerance and high regioselectivity. The possible pathway involved thiosulfonates were activated through the energy transfer route promoted by photocatalysis.

A Journey from June 2018 to October 2021 with N,N-Dimethylformamide and N,N-Dimethylacetamide as Reactants

A rich array of reactions occur using N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc) as reactants, these two amides being able to deliver their own H, C, N, and O atoms for the synthesis of a variety of compounds. This account highlights the literature published since June 2018, completing previous reviews by the author.

Visible-light-promoted synthesis of secondary and tertiary thiocarbamates from thiosulfonates and N-substituted formamides

A general visible-light-promoted metal-free synthesis of secondary and tertiary thiocarbamates starting from thiosulfonates and N-substituted formamides is developed. By employing rhodamine B as a photocatalyst and tert-butyl hydroperoxide (TBHP) as an oxidant, a wide scope of thiocarbamates can be obtained through direct thiolation of acyl C-H bonds under irradiation of blue light at room temperature for 12 h.

Selective oxidative intermolecular carbosulphenylation of aryl alkenes with thiols and nucleophiles via a 1,2-dithioethane intermediate

A periodate lithium-oxidized difunctionalisation of aryl alkenes with thiols and electron-rich aromatics was achieved, selectively affording more than thirty carbosulphenylated products. Both experiments and quantum chemical calculations demonstrated the radical-polar nature of the processes, and that 1,2-dithioethane and thiiranium ions might play the role of intermediates.

Nickel-Catalyzed Reductive Thiolation of Unactivated Alkyl Bromides and Arenesulfonyl Cyanides

The cross-electrophile coupling between unactivated alkyl bromides with arenesulfonyl cyanides catalyzed by Ni(acac)₂ under reductive conditions to form unsymmetrical sulfides is developed. This approach for sulfide synthesis is practical, relies on available, unfunctionalized materials such as alkyl (pseudo)halides, and is scalable. This catalytic strategy provides a complementary method for the preparation of unsymmetrical alkyl-aryl sulfides under mild conditions with good functional group tolerance.

Atom Transfer Radical Addition to Styrenes with Thiosulfonates Enabled by Synergetic Copper/Photoredox Catalysis

A synergetic copper/photoredox catalyzed ATRA of styrenes and thiosulfonates is developed. Besides aryl ethylenes, the challenging α-substituted styrenes were employed to construct the benzylic quaternary carbon centers. Owing to the mild conditions as well as the high level of substrate compability, this ATRA could be applied to derivatize bioactive natural products in late stage, and to install fluorophores across alkenes. The mechanistic studies reveal sulfonyl radicals as the key intermediate in the transformation.

Visible-light-promoted sulfonylation of thiols with aryldiazonium and sodium metabisulphite leading to unsymmetrical thiosulfonates

A facile visible-light-mediated protocol has been proposed for the synthesis of thiosulfonates via rhodamine 6G catalyzed sulfonylation of thiols with aryldiazonium and sodium metabisulphite at room temperature.

Metal-Free Radical Annulation of Oxygen-Containing 1,7-Enynes: Configuration-Selective Synthesis of (E)-3-((Arylsulfonyl)methyl)-4-Substituted Arylidenechromene Derivatives

A novel strategy for the synthesis of (E)-3-((arylsulfonyl)methyl)-4-substituted benzylidenechromene derivatives via a metal-free radical annulation reaction of oxygen-containing 1,7-enynes with thiosulfonates has been developed. The reaction shows broad substrate scope, wide functional group tolerance, and moderate to excellent yields. Moreover, thiosulfonates were well driven to achieve the bifunctionalization reaction of oxo-1,7-enynes which derived from aliphatic alkynes. In addition, the (E)-configuration of the products was highly controlled by the structure of 1,7-enyne.

Organic-photoredox-catalyzed three-component sulfonylative pyridylation of styrenes

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of styrenes via organic-photoredox catalysis is described. This metal-free process enables the direct and selective installation of sulfonyl and heteroaryl motifs and tolerates a wide array of functional groups as well as complex molecular scaffolds, that could complement previous methods and would be of interest in pharmaceutical research.

An efficient, metal-free protocol for the three-component sulfonylative pyridylation of alkenes via organic-photoredox catalysis is described.

Recent developments in the difunctionalization of alkenes with C–N bond formation

Various alkene difunctionalization reactions involving nitridization, diamination, azidation, oxyamination, carboamination, aminohalogenation, and nitration are introduced in this review.

Metal-Free Chemoselective Reaction of Sulfoxonium Ylides and Thiosulfonates: Diverse Synthesis of 1,4-Diketones, Aryl Sulfursulfoxonium Ylides, and β-Keto Thiosulfones Derivatives

A diverse chemoselective insertion reaction of sulfoxonium ylides and thiosulfonates under transition-metal-free conditions is developed, which successfully affords 1,4-diketone compounds, arylthiosulfoxide-ylides, and β-keto thiosulfones, respectively. The nucleophilic addition of two molecular sulfoxonium ylides to construct sulfone-substituted 1,4-dione compounds is the highlight of this work.