Three-component 1,2-dicarbofunctionalization of alkenes involving alkyl radicals

Tosylhydrazide-Induced 1,6-Enyne Radical Cyclization under Copper Catalysis: Access to 3,4-Dihydronaphthalen-1(2H)-one Derivatives

We describe an approach to access 4-aroyl-3-aryl-3,4-dihydronaphthalen-1(2H)-one derivatives in 41-79% yields through the Cu-catalyzed radical cyclization/desulfonylation of 1,6-enynes with tosylhydrazide under air conditions. This alternative desulfonylation strategy combines mild conditions, external oxidant-free processes, and sustainability, contributing to more environmentally friendly organic synthesis. The mechanistic studies showed that the CuCl/O2 combination serves as the source of the oxygen atom needed to form the C═O bond. The existence of tosylhydrazide is crucial for this conversion.

Stereoselective Fe-Catalyzed Decoupled Cross-Couplings: Chiral Vinyl Oxazolidinones as Effective Radical Lynchpins for Diastereoselective C(sp2)-C(sp3) Bond Formation

Modular, catalytic, and stereoselective methods for the dicarbofunctionalization of alkenes can streamline the synthesis of chiral active pharmaceutical ingredients (APIs) and agrochemicals. However, despite the inherent attractive properties of iron as catalysts for practical pharmaceutical synthesis (i.e., less expensive, more abundant, less toxic, and lower carbon footprint in comparison to other transition metals), iron-based catalytic methods that enable highly stereoselective dicarbofunctionalization of alkenes are lacking. Herein, we report the use of readily available chiral vinyl oxazolidinones as effective chiral radical lynchpins to enable practical and diastereoselective (up to 1:78 dr) Fe-catalyzed dicarbofunctionalization with fluoroalkyl halides and hetero(aryl) Grignard reagents. Experimental and computational mechanistic studies are carried out to elucidate the origin of stereoinduction and to build a stereochemical model for the rational reaction design.

Aerobic Copper-Catalyzed Oxysulfonylation of Vinylarenes with Sodium Sulfinates under Mild Conditions: A Modular Synthesis of β-Ketosulfones

An aerobic copper-catalyzed oxysulfonylation of vinylarenes with sodium sulfinates is described. This protocol features mild reaction conditions, convenient operation, and broad substrate scope with respect to vinylarenes and sodium sulfinates. Notably, the protocol demonstrates excellent tolerance of functional groups such as chloro, bromo, ester, cyano, and nitro groups. Mechanistic investigations indicated that the reaction should undergo radical cascades involving a sulfonyl radical generated from sodium sulfinate with air as the terminal oxidant, addition across alkene to deliver a benzylic radical, and subsequent cross-coupling with air.

Intermolecular Regioselective Alkylarylation of Vinylarenes via Photoredox/Nickel Dual Catalysis

A novel photoredox/nickel dual catalytic intermolecular alkylarylation of vinylarenes with tertiary and secondary alkyltrifluoroborates and aryl bromides is described, which affords 1,1-diarylalkane frameworks that are found in various natural products as well as functionalized molecules in good to excellent yield and regioselectivity through a radical relay process. Notably, this redox-neutral reaction could proceed efficiently with good tolerance of various substrates, including a great diversity of commercially available (hetero)aryl bromides, alkyltrifluoroborates, and vinylarenes.

Recent advances in dual photoredox/nickel catalyzed alkene carbofunctionalised reactions

Alkene carbofunctionalization reactions have great potential for synthesizing complex molecules and constructing complex structures in natural products and medicinal chemistry. Recently, dual photoredox/nickel catalysis has emerged as a novel strategy for alkene carbofunctionalization. Nickel offers numerous advantages over other transition metals, such as cost-effectiveness, abundance, and low toxicity, and moreover, it has many oxidation states. Nickel catalysts exhibit excellent catalytic activity in dual photoredox/transition metal catalysis, facilitating the formation of carbon-carbon or carbon-heteroatom bonds in organic transformations. This review highlights the latest advancements in dual photoredox/nickel-catalyzed alkene carbofunctionalizations and includes the literature published from 2020 to 2024.

Photoredox-catalyzed alkylarylation of activated alkenes via a ring-opening/Truce-Smiles rearrangement cascade

A photoredox-catalyzed alkylarylation of activated alkenes via a radical C-C bond cleavage/Truce-Smiles rearrangement cascade is developed. The protocol features mild and redox-neutral conditions, broad substrate scope and excellent functional group compatibility, providing a facile and efficient approach to the long-chain distal keto-amides with all-carbon quaternary centers at the alpha position.

A free-radical design featuring an intramolecular migration for a synthetically versatile alkyl-(hetero)arylation of simple olefins

A free-radical approach has enabled the development of a synthetically versatile alkyl-(hetero)arylation of olefins. Alkyl and (hetero)aryl groups were added concurrently to a full suite of mono- to tetrasubstituted simple alkenes (i.e., without requiring directing or electronically activating groups) for the first time. Key advances also included the introduction of synthetically diversifiable alkyl groups featuring different degrees of substitution, good diastereocontrol in both cyclic and acyclic settings, the addition of biologically valuable heteroarenes featuring Lewis basic nitrogen atoms as well as simple benzenes, and the generation of either tertiary or quaternary benzylic centers. The synthetic potential of this transformation was demonstrated by leveraging it as the key step in a concise synthesis of oliceridine, a new painkiller that received FDA approval in 2020.

Visible-Light-Induced Photoredox 1,2-Dialkylation of Styrenes with α-Carbonyl Alkyl Bromides and Pyridin-1-ium Salts

A visible-light-driven photoredox dialkylation of styrenes with α-carbonyl alkyl bromides and pyridin-1-ium salts for the synthesis of polysubstituted 1,4-dihydropyridines is reported. This reaction enables the formation of two new C(sp3)-C(sp3) bonds in a single reaction step and provides a strategy that employs pyridin-1-ium salts as the functionalized alkylating reagents via dearomatization to directly trap the resulting alkyl radicals from radical addition of alkenes and then terminate the alkene dialkylation.

Nickel/Photo-Cocatalyzed Three-Component Alkyl-Acylation of Aryl-Activated Alkenes

Herein, we disclose a nickel/photo-cocatalyzed three-component alkyl-acylation of aryl-substituted alkenes with aldehydes and electron-withdrawing-group-activated alkyl bromides, providing straightforward access to various ketones under mild and ligand-free conditions. The photocatalyst TBADT plays a dual role in activating the acyl C-H bond of aldehydes via hydrogen atom transfer and reducing the C-Br bond of alkyl bromides via single-electron transfer. While the terminal C-C bond is forged through polarity-matched radical-type addition, nickel is likely involved in the acylation step.

Nickel-Catalyzed 8-Aminoquinoline Directed Reductive Dialkylcyclization/Homodialkylation of Unactivated Alkenes

Chemo and regioselective dialkylation of alkene is an efficient protocol for constructing useful chemicals, but challenges remain in the unrestricted application of alkylating reagents. Alkyl bromide belongs to the easy-to-access and operable alkyl electrophiles that can be used in reductive coupling with alkenes. Here, we reported convenient strategies for dialkylcyclization and homodialkylation of unactivated β,γ- and γ,δ-unsaturated alkenyl amides with 1,3-dibromoalkanes or primary alkyl bromides under nickel-catalyzed reductive conditions that exhibited high regioselectivity and functional-group tolerance.

Visible Light Induced Three-Component 1,2-Dicarbofunctionalization of Alkenes and Alkynes

Harnessing visible-light in organic synthesis is one of the most effective methods that aligns with green and sustainable chemistry principles and hence skyrocketed in the last two decades. Similarly, three-component 1,2-dicarbofunctionalization of alkenes and alkynes has recently been a great choice to construct complex molecular systems in an easy and rapid manner. Therefore, light-induced reactions can be an excellent alternative to carry out 1,2-dicarbofunctionalization reactions, and very recently, organic chemists across the globe have fascinated us with their interesting articles. In this present review, we have summarized the recent advancements in the area of visible light induced three-component 1,2-dicarbofunctionalization of alkenes and alkynes till March 2023. We have categorized the discussion based on the catalysts used to carry out the transformations for better understanding and different important aspects of these transformations have also been covered.

Regioselective Fluoroalkylarylation of Enamides Enabled by an Iron-Catalyzed Multicomponent Radical Cross-Coupling Strategy

Fluoroalkylated compounds are important entities in agrochemicals, pharmaceuticals, and materials. The catalytic dicarbofunctionalization of alkenes represents a powerful strategy for the rapid construction and diversification of compounds. In this vein, multicomponent cross-coupling reactions (MC-CCR) can provide an efficient synthetic route to build molecular complexity. In this work, we report the first iron-catalyzed three-component fluoroalkylarylation of enamides via selective formation and trapping of α-amide radicals under mild conditions and fast reaction times. The reaction tolerates a variety of commercially available aryl Grignard reagents and fluoroalkyl halides. Finally, the use of a removable phthalimido group provides an efficient strategy to prepare highly valuable γ-difluoroalkylated amines.

Nickel-Catalyzed Regioselective Intermolecular Dialkylation of Alkenylarenes: Generation of Two Vicinal C(sp3 )-C(sp3 ) Bonds Across Alkenes

We disclose a Ni-catalyzed regioselective dialkylation reaction of alkenylarenes with α-halocarbonyls and alkylzinc reagents. The reaction produces γ-arylated alkanecarbonyl compounds with the generation of two new C(sp3 )-C(sp3 ) bonds at the vicinal carbons of alkenes. This reaction is effective for the use of primary, secondary and tertiary α-halocarboxylic esters, amides and ketones in conjunction with primary and secondary alkylzinc reagents as the sources of two C(sp3 ) carbons for the dialkylation of terminal and cyclic internal alkenes.

Divergent Construction of Azaheterocycles via Alkoxyl Radical-Triggered C-C Bond Cleavage/Cyclization of N-Functionalized Acrylamides

An array of redox-neutral alkylation/cyclization cascade reactions of N-functionalized acrylamides with cycloalkyl hydroperoxides were achieved via the alkoxyl radical-triggered C-C bond cleavage. Through adjusting the radical acceptors on the N atom, a variety of keto-alkylated chain-containing azaheterocycles, including indolo[2,1-a]isoquinolin-6(5H)-ones, quinoline-2,4-diones, and pyrido[4,3,2-gh]phenanthridines were constructed by a one-pot procedure with good yields and excellent functional group tolerance.

Lewis Acid Promoted Vicinal Oxytrifluoromethylselenolation of Alkenes

Herein, we have developed a metal-free, Lewis acid promoted vicinal oxytrifluoromethylselenolation of alkenes using trifluoromethyl selenoxides as electrophilic trifluoromethylselenolation reagents and alcohols as nucleophiles. With less steric and good nucleophilic solvents (such as ethanol and methol), Tf₂O-catalyzed oxytrifluoromethylselenolation could be realized, while stoichiometric Tf₂O was required to promote full transformation with less nucleophilic and steric solvents (such as isopropanol and tert-butanol). The reaction featured good substrate scope, functional group compatibility, and diastereoselectivity. This method could be further applied to oxytrifluoromethylselenolation, aminotrifluoromethylselenolation with stoichiometric nucleophiles under modified conditions. A mechanism involving a seleniranium ion was proposed based on the preliminary results.

General Method for Selective Three-Component Carboacylation of Alkenes via Visible-Light Dual Photoredox/Nickel Catalysis

A photoredox/nickel dual catalytic protocol for the regioselective three-component carboacylation of alkenes with tertiary and secondary alkyltrifluoroborates as well as acyl chlorides is described. This redox-neutral protocol can be applied to the rapid synthesis of ketones with high diversity and complexity via a radical relay process. Many functional groups, allowing for various commercially available acyl chlorides, alkyltrifluoroborates, and alkenes, are tolerated under these mild conditions.

Visible-Light-Photocatalyzed Dicarbofunctionalization of Conjugated Alkenes with Ketone-Based Dihydroquinazolinones

A visible-light-photocatalyzed 1,2-arylalkylation of N-(arylsulfonyl)acrylamides with ketone-based dihydroquinazolinones is described. The formal C-C bond cleavage of aliphatic ketones is unified with tandem radical alkylation/1,4-aryl migration/desulfonylation to forge two different types of vicinal C-C bonds and construct an all-carbon quaternary α-stereocenter, thus enhancing the carbogenic complexity and tolerating diverse functionalities. Additional to telescopic synthesis and product diversification, this method features a radical dicarbofunctionalization of conjugated N-(arylsulfonyl)acrylamides with a nucleophilic alkyl radical precursor (dihydroquinazolinone) utilizing oxygen as a green oxidant at ambient temperature.

Fe-Catalyzed Alkylazidation of α-Trifluoromethylalkenes: An Access to Quaternary Stereocenters Containing CF3 and N3 Groups

A concise Fe-catalyzed alkylazidation of α-trifluoromethylalkenes via a C-C bond cleavage/radical addition/azidation cascade is described. This protocol features a broad substrate scope, excellent functional group compatibility, and the ability to be performed on a gram scale, thus offering a practical and step-economic approach to the synthetically useful tertiary α-trifluoromethyl azides.

Regioselective Ni-Catalyzed reductive alkylsilylation of acrylonitrile with unactivated alkyl bromides and chlorosilanes

Transition-metal catalyzed carbosilylation of alkenes using carbon electrophiles and silylmetal (-B, -Zn) reagents as the nucleophiles offers a powerful strategy for synthesizing organosilicones, by incorporating carbon and silyl groups across on C-C double bonds in one step. However, to the best of our knowledge, the study of silylative alkenes difunctionalization based on carbon and silyl electrophiles remains underdeveloped. Herein, we present an example of silylative alkylation of activated olefins with unactivated alkyl bromides and chlorosilanes as electrophiles under nickel catalysis. The main feature of this protocol is employing more easily accessible substrates including primary, secondary and tertiary alkyl bromides, as well as various chlorosilanes without using pre-generated organometallics. A wide range of alkylsilanes with diverse structures can be efficiently assembled in a single step, highlighting the good functionality tolerance of this approach. Furthermore, successful functionalization of bioactive molecules and synthetic applications using this method demonstrate its practicability.

Probing La and Ce Excited-State Reactivity with Resonant Two-Photon Ionization Spectroscopy

Dehydrogenation and C-C bond cleavage of 1-butyne by the excited states of La and Ce atoms are investigated in laser-ablation metal molecular beams. The excited states of the metal atoms are prepared by resonant excitation, detected by resonant two-photon ionization spectroscopy, and the reaction products are monitored by photoionization time-of-flight mass spectrometry. The reactivities of La* [5d²(³F)6p (⁴G_5/2°)] and Ce* [4f5d(³F°)6s6p(³P°) (⁵H₅)] excited states are observed to be higher than those of the initial states of the corresponding metal atoms. The higher reactivities of the excited states are attributed to their higher energies and favorable electron configurations to form two covalent bonds of the metal-insertion intermediates. Although both excited La and Ce atoms show increased reactivities, the enhancement for Ce is much more pronounced than that of La, which cannot be explained by electron configurations alone. The larger reactivity enhancement from the initial states to the excited state of the Ce atom than that of La is due to the longer lifetime of the Ce excited state.

The Merger of Benzophenone HAT Photocatalysis and Silyl Radical-Induced XAT Enables Both Nickel-Catalyzed Cross-Electrophile Coupling and 1,2-Dicarbofunctionalization of Olefins

A strategy for both cross-electrophile coupling and 1,2-dicarbofunctionalization of olefins has been developed. Carbon-centered radicals are generated from alkyl bromides by merging benzophenone hydrogen atom transfer (HAT) photocatalysis and silyl radical-induced halogen atom transfer (XAT) and are subsequently intercepted by a nickel catalyst to forge the targeted C(sp³)–C(sp²) and C(sp³)–C(sp³) bonds. The mild protocol is fast and scalable using flow technology, displays broad functional group tolerance, and is amenable to a wide variety of medicinally relevant moieties. Mechanistic investigations reveal that the ketone catalyst, upon photoexcitation, is responsible for the direct activation of the silicon-based XAT reagent (HAT-mediated XAT) that furnishes the targeted alkyl radical and is ultimately involved in the turnover of the nickel catalytic cycle.

Synthesis of Vicinal Carbocycles by Intramolecular Nickel-Catalyzed Conjunctive Cross-Electrophile Coupling Reaction

A nickel-catalyzed intramolecular conjunctive cross-electrophile coupling reaction has been established. This method enables the synthesis of 3,5-vicinal carbocyclic rings found in numerous biologically active compounds and natural products. We provide mechanistic experiments that indicate this reaction proceeds through alkyl iodides formed in situ, initiates at the secondary electrophilic center, and proceeds through radical intermediates.

Palladium(II)-catalyzed enantioselective intermolecular oxidative diarylation of internal enamides

The construction of vicinal stereogenic centers via the simultaneous formation of two C-C bonds across alkenes under oxidative conditions is a stubborn challenge. Herein, we report a Pd(II)-catalyzed highly enantioselective intermolecular oxidative 1,2-diarylation reaction of internal enamides with aryl boronic acids, enabling the expedient construction of two vicinal stereocenters with excellent diastereo-, and enantioselectivities.

Photocatalytic selective 1,2-hydroxyacylmethylation of 1,3-dienes with sulfur ylides as source of alkyl radicals

Exploration of the zwitterionic property of sulfur ylides has long been known as a flexible strategy in a wide range of chemical transformations for different ring-sized construction. By contrast, their...