Visible-Light Mediated ortho-Trifluoromethylation of Aniline Derivatives

Direct Decarboxylation of Trifluoroacetates Enabled by Iron Photocatalysis

Trifluoroacetates are the most abundant and accessible sources of trifluoromethyl groups, which are key components in pharmaceuticals and agrochemicals. The generation of trifluoromethyl reactive radicals from trifluoroacetates requires their decarboxylation, which is hampered by their high oxidation potential. This constitutes a major challenge for redox-based methods, because of the need to pair the redox potentials with trifluoroacetate. Here we report a strategy based on iron photocatalysis to promote the direct photodecarboxylation of trifluoroacetates that displays reactivity features that escape from redox limitations. Our synthetic design has enabled the use of trifluoroacetates for the trifluoromethylation of more easily oxidizable organic substrates, offering new opportunities for late-stage derivatization campaigns using chemical feedstocks, Earth-abundant catalysts, and visible-light.

Recent Advances in Visible Light-Mediated Radical Fluoro-alkylation, -alkoxylation, -alkylthiolation, -alkylselenolation, and -alkylamination

In the last few years, many reagents and protocols have been developed to allow for the efficient fluorofunctionalization of a diverse set of scaffolds ranging from alkanes, alkenes, alkynes, and (hetero)arenes. The concomitant rise of organofluorine chemistry and visible light-mediated synthesis have synergistically expanded the fields and have mutually benefitted from developments in both fields. In this context, visible light driven formations of radicals containing fluorine have been a major focus for the discovery of new bioactive compounds. This review details the recent advances and progress made in visible light-mediated fluoroalkylation and heteroatom centered radical generation.

Dicarbofunctionalization of unactivated alkenes via organo-photoredox catalysis in water: access to cyanoalkylated fused quinazolinones

A visible light-induced C-C bond cleavage/addition/cyclization cascade of oxime esters and unactivated alkenes has been developed using water as the solvent. This green protocol offers an easy access to medicinally valuable cyanoalkylated quinazolinones. Mild reaction conditions, functional group tolerance and late-stage functionalization of complex molecules are the important features of this transformation.

Reduction of SF5CF3via iridium catalysis: radical trifluoromethylation of aromatics

The greenhouse gas SF₅CF₃ acts as CF₃ source for the photocatalytic trifluoromethylation of arenes on using [Ir(dtbbpy)(ppy)₂]PF₆ (4,4'-di-tert-butyl-2,2'-dipyridyl, ppy = 2-phenylpyridine) as catalyst. The trifluoromethylation of C₆D₆ in the presence of 1-octanol results in the concomitant generation of 1-fluorooctane, presumably by intermediate SF₄.

Copper-assisted trifluoromethylthiolation/radical cascade cyclization of alkynes to construct SCF3-containing dioxodibenzothiazepines

A mild and efficient Cu-assisted trifluoromethylthiolation/radical cascade cyclization of alkynes with readily available and stable AgSCF₃ as the trifluoromethylthiolating reagent has been disclosed. This transformation provides an opportunity to construct a series of potential medicinally valuable trifluoromethylthio-substituted dioxodibenzothiazepines with wide functional group compatibility. This protocol opens up a new avenue for the construction of useful trifluoromethylthiolated seven-membered N-heterocycles.

Selective Nickel-Catalyzed Hydrodefluorination of Amides Using Sodium Borohydride

Hydrodefluorination selective to the ortho position to amides is accomplished under mild conditions using sodium borohydride and a nickel catalyst. The facile formation of a nickelacycle intermediate with a specific geometry ensures selectivity without the need for electronic directing groups, and fluorine atoms in other positions remain intact. This method avoids the use of stoichiometric silanes which are typical for most other defluorination reactions, resulting in virtually no organic waste byproducts.

Organophotoredox-catalyzed cyanoalkylation of 1,4-quinones

A visible-light-induced metal-free cyanoalkylation of 1,4-quinones under mild and redox-neutral conditions is described. This reaction proceeds at room temperature without the need of extra base or additive and is suitable for a variety of 1,4-quinones and differently substituted cyclobutanone oxime esters. Further transformation of cyano functionality to tetrazole and amine has also been demonstrated to showcase the advantage of this method to prepare drug-like molecules.

CF3SO2Na-Mediated Visible-Light-Induced Cross-Dehydrogenative Coupling of Heteroarenes with Aliphatic C(sp3)-H Bonds

Minisci-type reaction is one of the important means to construct C(sp³)-H functionalization of heteroarenes. According to traditional methods, stoichiometric amounts of precious transition metal catalysts and chemical oxidants were required at high temperatures. Here, a green and gentle novel Minisci-type method was developed via visible-light-induced cross-dehydrogenative coupling of heteroarenes with aliphatic C(sp³)-H bonds under oxidant-free and transition-metal-catalyst-free conditions. Only the catalytic equivalent of CF₃SO₂Na and room temperature were required to maintain an efficient reaction.

Divergent cyanoalkylation/cyanoalkylsulfonylation of enamides under organophotoredox catalytic conditions

An organophotoredox catalyzed divergent cyanoalkylation/cyanoalkylsulfonylation of enamides is described.

Visible-light-promoted direct C3-trifluoromethylation and perfluoroalkylation of imidazopyridines

An efficient method for direct trifluoromethylation and perfluoroalkylation at C3 of imidazopyridines through visible light-promoted C-H bond functionalization was developed. Under the irradiation of a blue LED, a series of C3-perfluoroalkyl-substituted imidazopyridines were synthesized from the corresponding imidazopyridines and perfluoroalkyl iodides in moderate to good yields at room temperature. It should be mentioned that this reaction proceeded in the absence of any transition-metal catalyst, oxidant and photocatalyst.

Photoredox-Catalyst-Enabled para-Selective Trifluoromethylation of tert-Butyl Arylcarbamates

The direct incorporation of a trifluoromethyl group on an aromatic ring using a radical pathway has been extensively investigated. However, the direct highly para-selective C-H trifluoromethylation of a class of arenes has not been achieved. In this study, we report a light-promoted 4,5-dichlorofluorescein (DCFS)-enabled para-selective C-H trifluoromethylation of arylcarbamates using Langlois reagent. The preliminary mechanistic study revealed that the activated organic photocatalyst coordinated with the arylcarbamate led to para-selective C-H trifluoromethylation. Ten-gram scale reaction performs well highlighting the synthetic importance of this new protocol.

Iridium-catalyzed regioselective C-H sulfonamidation of 1,2,4-thiadiazoles with sulfonyl azides in water

We have developed a regioselective C-N cross-coupling of 1,2,4-thiadiazoles with sulfonyl azides through iridium catalysis in water. This method tactically linked the 1,2,4-thiadiazoles and sulfonamides together, and the novel molecules increased the diversity of 1,2,4-thiadiazoles which may have potential applications.

Metallaphotoredox catalysis with organic dyes

Here…comes the fun…Combination of metals and organic photocatalysts allows the practical invention of new methodologies!

A facile method for Rh-catalyzed decarbonylative ortho-C–H alkylation of (hetero)arenes with alkyl carboxylic acids

A facile and effective method for Rh-catalyzed direct ortho-alkylation of C–H bonds in (hetero)arenes with commercially available carboxylic acids has been developed. This strategy was initiated by in situ conversion of carboxylic acids to anhydrides which, without isolation, underwent Rh-catalyzed direct decarbonylative cross-coupling of aryl carboxamides containing 8-aminoquinoline. The reaction proceeds with high regioselectivity and exhibits a broad substrate scope as well as functional group tolerance.

A facile and effective method for Rh-catalyzed direct ortho-alkylation of C–H bonds in (hetero)arenes with commercially available carboxylic acids has been developed.

An Indirect Strategy for Trifluoromethylation via an Iridium Catalyst: Approach to Generate Isocoumarin Skeletons in Bioactive Molecules

3-Bromo-1,1,1-trifluoroacetone was first disclosed as an effective indirect trifluoromethylation reagent to construct the important 3-trifluoromethyl isocoumarin skeleton. The reaction proceeds through a ligand-promoted, iridium-catalyzed ortho-selective C-H alkylation of benzoic acid and an intermolecular cyclization reaction promoted by silver acetate. A wide range of 3-trifluoromethyl isocoumarins can be easily obtained in moderate to good yields. Importantly, the isocoumarin skeleton can be easily formed in bioactive compounds, highlighting the importance of this reaction.

Synthesis of monofluorooxazoles with quaternary C-F centers through photoredox-catalyzed radical addition of methylene-2-oxazolines

A novel photoredox-catalyzed radical addition of methylene-2-oxazolines has been developed under visible light irradiation to synthesize monofluorooxazoles with a quaternary carbon center using 2-bromo-2-fluoro-3-oxo-3-phenylpropionates as radical source. This method with a simple protocol, scalability and high yield offers a facile path to get diverse monofluorinated oxazoles with quaternary C-F centers, which are a class of highly valuable motifs and synthons.

Modular synthesis of (C-10 to C-13)-substituted-9,14-diaryl-9,14-dihydrodibenzo[a,c]phenazines via a subsequent Buchwald-Hartwig amination and C-H amination strategy

Herein, we report a modular synthetic approach of (C-10 to C-13)-substituted 9,14-diaryl-9,14-dihydrodibenzo[a,c]phenazine derivatives. This synthetic route enables the aromatic substitution in a predictable and programmed manner to obtain products in synthetically useful isolated yield.

Metal-free late-stage C(sp2)-H functionalization of N-aryl amines with various sodium salts

Metal-free consecutive C(sp2)-X (X = Cl, Br, S, N) bond formations of N-aryl amines (cyclic, fused, carbamate, and aminium radicals) were achieved under mild conditions using [bis(trifluoroacetoxy)iodo]benzene (PIFA) and simple nonharmful sodium salts. This direct and selective C(sp2)-H functionalization showed excellent functional group compatibility, cost effectiveness, and late-stage applicability for the synthesis of biologically active natural products. Two mechanisms were proposed to explain the ortho- or para-preference, as well as the accelerating effect of CH3NO2.

Palladium(ii)-catalyzed vinylic geminal double C-H activation and alkyne annulation reaction: synthesis of pentafulvenes

The first transition-metal-catalyzed vinylic geminal double C(sp²)-H activation and di-substituted alkyne annulation reaction is reported. This palladium(ii)-catalyzed, amide directed reaction of vinylic compounds with di-substituted alkynes offers an efficient synthetic path to pentafulvenes, which are very important compounds because of their bioactivity and interesting optical properties. A FeCl₃-mediated transformation of pentafulvenes to fluorescent cyclopenta[b]quinolines is also developed.

Visible-light-induced [4 + 2] cycloaddition of pentafulvenes by organic photoredox catalysis

We have developed thioxanthylium photoredox catalyzed [4 + 2] cycloaddition of pentafulvenes at room temperature under green light irradiation, which affords tetrahydrocyclopenta[b]chromenes with high regioselectivities. The present reaction provides a sustainable approach to carry out the cycloaddition of pentafulvenes without the use of transition metal catalysts or high-temperature conditions. This procedure enables a mild and straightforward access to 1,3a,9,9a-tetrahydrocyclopenta[b]chromenes. The quantum yield of the reaction (Φ = 0.15) indicates that the reaction would mainly proceed via photocatalytic pathways.

A directing group free Pd(ii)-catalysed desulfitative C6-arylation of 2-pyridone using an arylsulfonyl chloride

Heteroatom-containing directing group free C6-arylation of 2-pyridone.

Recent advances in the direct β-C(sp2)–H functionalization of enamides

Recent advances in the direct β-C(sp²)–H functionalization of enamides, mainly including arylation, alkenylation, alkynylation, alkylation, acylation, sulfonylation, phosphorylation, and others, are reported.

Cp*CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

A Cp*Co^III-catalyzed arene C–H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope.