Stereoselective Photoredox-Catalyzed Chlorotrifluoromethylation of Alkynes: Synthesis of Tetrasubstituted Alkenes

Electron-donor-acceptor (EDA) complex-driven regioselective vicinal and oxidative geminal functionalization of alkynes

A visible-light-initiated electron-donor-acceptor (EDA) complex-driven regioselective vicinal and oxidative geminal thiosulfonylation of alkynes is presented. Organic thiosulfonates act as an acceptor, producing either sulfonyl (RSO2˙) or thiyl (RS˙) radicals under base and solvent switchable conditions. Simultaneous installation of three different functionalities, viz carbonyl, sulfonyl, and thiyl, takes place under one condition, while another condition leads to vicinal thiolation and sulfonylation.

Ligand-Controlled Copper-Catalyzed Halo-Halodifluoromethylation of Alkenes and Alkynes Using Fluorinated Carboxylic Anhydrides

Polyhalogenated molecules are often found as bioactive compounds in nature and are used as synthetic building blocks. Fluoroalkyl compounds hold promise for the development of novel pharmaceuticals and agrochemicals, as the introduction of fluoroalkyl groups is known to improve lipophilicity, membrane permeability, and metabolic stability. Three-component 1,2-halo-halodifluoromethylation reactions of alkenes are useful for their synthesis. However, general methods enabling the introduction of halodifluoromethyl (CF2X) and halogen (X') groups in the desired combination of X and X' are lacking. To address this gap, for the first time, we report a three-component halo-halodifluoromethylation of alkenes and alkynes using combinations of commercially available fluorinated carboxylic anhydrides ((CF2XCO)2O, X=Cl and Br) and alkali metal halides (X'=Cl and Br). In situ prepared fluorinated diacyl peroxides were identified as important intermediates, and the use of appropriate bipyridyl-based ligands and a copper catalyst was essential for achieving high product selectivity. The synthetic utility of the polyhalogenated products was demonstrated by exploiting differences in the reactivities of their C-X and C-X' bonds to achieve selective derivatization. Finally, the reaction mechanism and ligand effect were investigated using experimental and theoretical methods to provide important insights for the further development of catalytic reactions.

Visible Light-Induced Copper-Catalyzed Regio- and Stereoselective Difluoroalkylthiocyanation of Alkynes

The first regio- and stereoselective difluoroalkylthiocyanation of alkynes with BrCF2R and KSCN has been disclosed under visible light-induced copper catalysis. The copper complex photosensitizer formed in situ not only promotes the generation of CF2-alkyl radicals but also facilitates the construction of C-SCN bonds, allowing the reaction to proceed smoothly without any additional photocatalysts or radical initiators. Moreover, the challenging internal alkynes can also be transformed to deliver CF2-derived tetrasubstituted olefins with potential applications in agricultural and medicinal chemistry.

Visible light-mediated halogenation of organic compounds

The use of visible light and photoredox catalysis emerged as a powerful and sustainable tool for organic synthesis, showing high value for distinctly different ways of bond creation. Halogenated compounds are the cornerstone of contemporary organic synthesis: it is almost impossible to develop a route towards a pharmaceutical reagent, agrochemical, natural product, etc. without the involvement of halogen-containing intermediates. Moreover, the halogenated derivatives as final products became indispensable for drug discovery and materials science. The idea of this review is to understand and summarise the impact of visible light-promoted chemistry on halogenation and halofunctionalisation reactions.

Photoredox-Catalyzed Chlorotrifluoromethylation of Arylallenes: Synthesis of a Trifluoromethyl Building Block

A new class of trifluoromethyl building blocks─2-trifluoromethyl allyl chlorides─have been obtained through a photoredox-catalyzed chlorotrifluoromethylation of aryl allenes. The reaction proceeded in a regio- and stereoselective manner. A trifluoromethylated analog of the flunarizine drug was synthesized.

Difluoromethylsulfonyl Imidazolium Salt for Difluoromethylation of Alkenes

Herein, we describe the design and synthesis of a difluoromethylsulfonyl imidazolium salt, which can act as a radical difluoromethylation reagent to achieve the challenging amino- and oxy-difluoromethylation of alkenes. Notably, the three steps for the synthesis of the imidazolium salt do not require any tedious distillation or column chromatography purification process, and the amino- and oxy-difluoromethylation paths are simply determined by the selection of reaction solvents.

Photoinduced Trifluoromethylation with CF3Br as a Trifluoromethyl Source: Synthesis of α-CF3-Substituted Ketones

An efficient and novel photoinduced trifluoromethylation employing CF₃Br as a trifluoromethyl source is described. With commercially accessible fac-Ir^(III)(ppy)₃ as the catalyst, radical trifluoromethylation between O-silyl enol ether and CF₃Br occurs successfully. This method provides various α-CF₃-substituted ketones with a broad substrate scope in good yields under mild reaction conditions.

A diastereoselective synthesis of cyclopentanones via photocatalytic reductive alkyltrifluoromethylation of ynones

A photocatalytic reductive alkyltrifluoromethylation of ynones with the Langlois reagent is developed, providing a regio- and diastereoselective access to trifluoromethylated cyclopentanones under mild conditions.

Recent Advances on the Halo- and Cyano-Trifluoromethylation of Alkenes and Alkynes

Incorporation of fluorine into organic molecules is a well-established strategy in the design of advanced materials, agrochemicals, and pharmaceuticals. Among numerous modern synthetic approaches, functionalization of unsaturated bonds with simultaneous addition of trifluoromethyl group along with other substituents is currently one of the most attractive methods undergoing wide-ranging development. In this review article, we discuss the most significant contributions made in this area during the last decade (2012−2021). The reactions reviewed in this work include chloro-, bromo-, iodo-, fluoro- and cyano-trifluoromethylation of alkenes and alkynes.

Recent progress in the radical α-C(sp3)-H functionalization of ketones

The direct use structurally simple ketones as α-ketone radical sources for α-C(sp³)-H functionalization is a sustainable and powerful approach for constructing complex and multifunctional chemical scaffolds with diverse applications. The reactions of α-ketone radicals with alkenes, alkynes, enynes, imides, and imidazo[1,2-a]pyridines have broadened the structural diversity and complexity of ketones. Through chosen illustrative examples, we outline the recent progress in the development of methods that enable the radical α-C(sp³)-H functionalization of ketones, with an emphasis on radical initiation systems and possible mechanisms of the transformations. The application of these strategies is illustrated by the synthesis of several biologically active molecules and drug molecules. Further subdivision is based on substrate type and reaction type.

Recent advances in the stereoselective synthesis of acyclic all-carbon tetrasubstituted alkenes

Alkenes bearing four carbon-based groups are ubiquitous motifs in chemical sciences due to their various applications from medicinal to materials chemistry, and as chemical platforms for the synthesis of complex, chiral molecules. As such, tremendous research efforts are currently ongoing in order to develop general procedures for the challenging stereoselective synthesis of all-carbon tetrasubstituted alkenes, especially for acyclic structures. Since classical approaches to carbon-carbon double bonds are not suitable for the high steric demand around tetrasubstituted alkenes, a variety of unique approaches to access these privileged functional groups have been developed in recent years. This review article highlights the most significant developments in the field from 2007 to 2020, with an emphasis on the mechanisms and remaining limitations of these contemporary methods. Specifically, recent advances in internal alkyne carbofunctionalizations, in multicomponent couplings or other cross-couplings from nucleophilic or electrophilic alkenyl partners, and in the development of miscellaneous methods, are discussed.

Diethylzinc-Mediated Radical 1,2-Addition of Alkenes and Alkynes

A novel diethylzinc-mediated radical 1,2-addition of perfluoroalkyl iodides to unactivated alkenes and alkynes is presented, which demonstrates a novel way to generate an ethyl difluoroacetate radical. This method is highly efficient and gives full conversions of the substrates, high yields of the products, and negligible byproducts and requires no column chromatography purifications. The mild conditions enable this protocol to exhibit excellent functional group compatibility.

Halotrifluoromethylation of 1,3-Enynes: Access to Tetrasubstituted Allenes

A highly regioselective copper-catalyzed 1,4-chloro- and bromotrifluoromethylation of 1,3-enynes has been presented for the first time, which affords an efficient transformation to access halo- and CF₃-containing tetrasubstituted allene derivatives with good to excellent yield. This protocol is practical and convenient, in which a wide range of functional groups are compatible. Applications of this method for the gram-scale preparation and late-stage functionalization of biologically active molecules are also demonstrated.

Activation of different C–F bonds in fluoropolymers for Cu(0)-mediated single electron transfer radical polymerization

The graft polymerization of MMA initiated from PVDF-based fluoropolymers via single electron transfer controlled radical polymerization (SET-CRP) is reported.

Difunctionalization of Alkenes and Alkynes via Intermolecular Radical and Nucleophilic Additions

Popular and readily available alkenes and alkynes are good substrates for the preparation of functionalized molecules through radical and/or ionic addition reactions. Difunctionalization is a topic of current interest due to its high efficiency, substrate versatility, and operational simplicity. Presented in this article are radical addition followed by oxidation and nucleophilic addition reactions for difunctionalization of alkenes or alkynes. The difunctionalization could be accomplished through 1,2-addition (vicinal) and 1,n-addition (distal or remote) if H-atom or group-transfer is involved in the reaction process. A wide range of moieties, such as alkyl (R), perfluoroalkyl (R_f), aryl (Ar), hydroxy (OH), alkoxy (OR), acetatic (O₂CR), halogenic (X), amino (NR₂), azido (N₃), cyano (CN), as well as sulfur- and phosphorous-containing groups can be incorporated through the difunctionalization reactions. Radicals generated from peroxides or single electron transfer (SET) agents, under photoredox or electrochemical reactions are employed for the reactions.

AIBN-Induced Remote Trifluoromethyl-Alkynylation of Thioalkynes

A novel α,α'-azobis(isobutyronitrile) (AIBN)-induced remote trifluoromethyl-alkynylation of thioalkynes with alkynyl triflones as both the trifluoromethyl and alkyne sources is described. Structurally diverse trifluoromethylated (Z)-enynes can be constructed with full control of regio-, stereo-, and site-selectivity, which serves as a highly selective method for the rapid construction of trifluoromethylated molecules.

Photoredox-catalyzed halotrifluoromethylations of alkynes with triethylammonium halides: synthesis of tetrasubstituted alkenes containing CF3 and halogens

The introduction of F- and CF₃-groups into alkynes is enabled by photocatalysis under mild conditions. The developed method can be extended to providing chloro- and bromotrifluoromethylated alkynes and bioactive compounds functionalization.

Synthesis of α-Trifluoromethylacrylates by Ligand-Free Palladium-Catalyzed Mizoroki-Heck Reaction

Efficient ligand-free palladium catalyzed Mizoroki-Heck reaction allowed the formation of trisubstituted α-trifluoromethylacrylates. The reaction showed good chemical tolerance and furnished moderate to excellent yields of reaction. Silver salt additive proved to be essential for the reaction. The reaction has been then applied to the formation of 3-trifluoromethyl coumarins and analogues of therapeutic agents.

A convenient access to allylic triflones with allenes and triflyl chloride in the presence of (EtO)2P(O)H

A simple method for the preparation of allylic triflones from allenes and triflyl chloride in the presence of (EtO)₂P(O)H has been developed.

Copper-catalyzed aminothiolation of terminal alkynes with tunable regioselectivity

A simple, mild, and efficient catalytic aminothiolation of terminal alkynes for the synthesis of both 2- and 3-substituted thiazolo[3,2-a]benzimidazoles is established upon catalysis with copper(i), in which complementary regioselectivities could be achieved by using sterically different phenanthroline-based ligands.

Synthesis of fluoroalkylated alkynes via visible-light photocatalysis

Fluoroalkylated alkynes, which are versatile building blocks for the synthesis of various biologically active organofluorine compounds, were synthesized from easily available alkynyl halides and fluoroalkyl halides by visible-light photocatalysis.

Synthesis of tri-substituted allyl alcohols via a copper/iron co-catalyzed cascade perfluoroalkylation/rearrangement of aryl propynyl ethers

A copper/iron co-catalyzed fluoroalkylation of aryl propynyl ethers for the synthesis of perfluoroalkylated tri-substituted allyl alcohol derivatives is reported.

Rhodium-catalyzed alkenyl C–H functionalization with amides

Rhodium-catalyzed pyridyl-directed alkenyl C–H bond functionalization with aroyl- or acryl-amides via C–H/C–N activation was carried out.

Palladium-Catalyzed Domino Reaction for Stereoselective Synthesis of Multisubstituted Olefins: Construction of Blue Luminogens

The first Pd-catalyzed multicomponent reaction of aryl iodides, alkenyl bromides, and strained alkenes has been developed, which allowed us to synthesize a variety of multisubsituted olefins in yields of 45-96% with excellent stereoselectivity. The configuration of the product was controlled by the configuration of the alkenyl bromides. Moreover, this practical methodology employing readily available substrates was found to be tolerant to a wide range of functional groups. Fifty six examples of highly stereoselective tri- or tetrasubstituted olefins have been successfully synthesized via this methodology. Most of the synthesized tetrasubstituted olefins are good aggregation-induced emission (AIE) luminogens.