Atom-transfer radical addition of fluoroalkyl bromides to alkenes via a photoredox/copper catalytic system

Cu-Catalyzed Three-Component Alkene Carboamination: Mechanistic Insights and Rational Design to Overcome Limitations

Herein, we report mechanistic investigations into the Cu-catalyzed three-component carboamination of alkenes with α-halo carbonyls and aryl amines via an oxocarbenium intermediate. Monitoring the reaction reveals the formation of transient atom transfer radical addition (ATRA) intermediates with both electron-neutral and deficient vinyl arenes as well as unactivated alkenes. Based on our experimental studies and density functional theory calculations, the oxocarbenium is generated through atom transfer and subsequent intramolecular substitution. Further, mechanistic factors that dictate the regioselectivity of the nucleophilic attack onto the oxocarbenium to afford the γ-amino ester, γ-iminolactone, or γ-lactone are discussed. A strategy to overcome scope limitation with respect to unactivated alkenes is developed using the mechanistic insights gained herein. Finally, we demonstrate that under modified conditions, our Cu catalyst enables the ATRA reaction between a variety of alkyl halides and vinyl arenes/α-olefins, and we present a one-pot, two-step carbofunctionalization with an array of nucleophiles through ATRA/SN2.

10-Phenylphenothiazine-Organophotocatalyzed Bromo-Perfluoroalkylation of Unactivated Olefins

In this study, we have developed a smooth metal-free visible-light-induced bromo-perfluoroalkylation of unactivated olefins with the aid of 10-phenylphenothiazine (PTH) as an organic photoredox catalyst. The reaction is 100% atom-economic redox-neutral and proceeds with stoichiometric amounts of olefin and perfluoroalkyl bromide. To show the potential of these unexplored motifs, we carried out various postfunctionalizations taking advantage of the bromine atom, including gram-scale experiments.

Aggregation‐enabled alkene insertion into carbon–halogen bonds

Molecular aggregation affects the electronic interactions between molecules and has emerged as a powerful tool in material science. Aggregate effect finds wide applications in the research of new physical phenomena; however, its value for chemical reaction development has been far less explored. Herein, we report the development of aggregation‐enabled alkene insertion into carbon–halogen bonds. The spontaneous cleavage of C–X (X = Cl, Br, or I) bonds generates an intimate ion pair, which can be quickly captured by alkenes in an aggregated state. Additional catalysts or promoters are not necessary under such circumstances, and solvent quenching experiments indicate that the aggregated state is critical for achieving such sequences. The ionic insertion mode is supported by mechanistic studies, density functional theory calculations, and symmetry‐adapted perturbation theory analysis. Results also show that the non‐aggregated state may quench the transition state and terminate the insertion process.

Photoredox and Copper Dual-Catalyzed Cyclization of Alkyne-tethered α-Bromocarbonyls

The synergistic systems of photoredox and copper catalyst have already appeared as a novel formation of green synthetic chemistry, which open new avenues for chemical synthesis applications. We describe a novel strategy for the cyclization of alkyne-tethered α-bromocarbonyls initiated by the cleavage of C(sp3 )-Br bond via the collaboration of photoredox and copper catalyst. The present protocol exhibits mildness using economical copper catalyst and visible-light at room temperature. The gram-scale and sunlight irradiation experiments proceeded smoothly to show the practicality of the methodology. It is notable that the newly generated oxygen in the product originates from H2 O.

Copper-mediated bromine atom transfer radical cyclisation of unactivated alkyl bromides

The atom transfer radical cyclisation of unactivated alkyl bromides was realized by using a catalytic system of CuBr and Me₆-TREN. This protocol is applicable to the preparation of five-membered rings from unsaturated primary and secondary bromides.

Dual Photoredox/Copper Catalyzed Fluoroalkylative Alkene Difunctionalization

A method for performing radical difunctionalization of alkenes using fluorinated halides and a nucleophilic component (thiolate and iodide anions) is described. These nucleophilic fragments serve as redox active groups for performing subsequent transformations. The difunctionalization reaction involves photoredox generation of fluorinated radicals, their addition to the double bond followed by copper-promoted C-S or C-I bond formation. The primary products can be further coupled with silyl enol ethers, α-(trifluoromethyl)styrenes, and trimethylsilyl cyanide affording a variety of fluorinated compounds.

A three-component difunctionalization of N-alkenyl amides via organophotoredox radical-polar crossover

Herein, we report a three-component organophotoredox coupling of N-alkenyl amides with α-bromocarbonyls and various nucleophiles. This transition metal-free difunctionalization protocol installs sequential C-C and C-Y (Y = S/O/N) bonds in alkenes. This reaction works with terminal and internal alkenes containing both cyclic and acyclic amides via radical-polar crossover.

From Styrenes to Fluorinated Benzyl Bromides: A Photoinduced Difunctionalization via Atom Transfer Radical Addition

An operationally simple and practical method is disclosed to achieve the difunctionalization of styrenes, generating fluorinated benzyl bromides via a photoinduced atom transfer radical addition process. The developed method is mild, atom-economical, cost-effective, employs very low photocatalyst loading (1000 ppm), and is highly compatible with a broad range of functional groups on styrene. The versatility of the fluorinated benzyl bromides is demonstrated through their derivatization to a variety of valuable compounds.

Organophotoredox-Catalyzed Reductive Tetrafluoroalkylation of Alkenes

A method for the hydroperfluoroalkylation of alkenes with 1,2-dibromotetrafluoroethane leading to tetrafluorinated bromides is described. The reaction is conveniently performed under blue light irradiation using an organic photocatalyst and ascorbic acid as a reducing agent. Primary products can be further functionalized via radical pathways affording various tetrafluorinated compounds.

Subphthalocyanine capsules: molecular reactors for photoredox transformations of fullerenes

The internal cavity formed by a dimeric subphthalocyanine (SubPc) capsule (SubPc₂Pd₃, 2), ensembled by coordination of pyridyl substituents in the monomeric SubPc 1 to Pd centers, has proved an optimal space for the complexation of C₆₀ fullerene. Taking advantage of the intense absorption of green light of the SubPc component at around 550 nm, we have tested different green-light induced photoredox addition reactions over the double bonds of guest C₆₀. Both addition of amine radicals, generated by reductive quenching of the excited state of 2 by aromatic trimethylsilylamines, and addition of trifluoroethyl radicals, obtained from oxidative quenching of the photosensitizer, have successfully taken place with good yields in the 2:C₆₀ host:guest complex. On the other hand, both the photoredox reactions result in much lower yields when the monomeric pyridyl-SubPc is used as a photocatalyst, demonstrating that encapsulation results in a strong acceleration of the reaction. Importantly, this is the first example of the use of a confined microenvironment to trigger photoredox chemical transformations of fullerenes.

A photoredox cage built by coordination of two pyridyl-subphthalocyanines to Pd centers has proved versatile and efficient to catalyze photoredox addition reactions over encapsulated C₆₀.

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.