Review and Theoretical Analysis of Fluorinated Radicals in Direct CAr-H Functionalization of (Hetero)arenes

We highlight key contributions in the field of direct radical CAr- H (hetero)aromatic functionalization involving fluorinated radicals. A compilation of Functional Group Transfer Reagents and their diverse activation mechanisms leading to the release of radicals are discussed. The substrate scope for each radical is analyzed and classified into three categories according to the electronic properties of the substrates. Density functional theory computational analysis provides insights into the chemical reactivity of several fluorinated radicals through their electrophilicity and nucleophilicity parameters. Theoretical analysis of their reduction potentials also highlights the remarkable correlation between electrophilicity and oxidizing ability. It is also established that highly fluorinated radicals (e.g. ⋅OCF3) are capable of engaging in single-electron transfer (SET) processes rather than radical addition, which is in good agreement with experimental literature data. A reactivity scale, based on activation barrier of addition of these radicals to benzene is also elaborated using the high accuracy DLPNO-(U)CCSD(T) method.

Recent advances on non-precious metal-catalysed fluorination, difluoromethylation, trifluoromethylation, and perfluoroalkylation of N-heteroarenes

This review highlights the recent advances, from 2015 to 2023, on the introduction of organo-fluorine derivatives at the N-heteroarene core. Notable features considering new technologies based on organofluorine compounds such as: (i) approaches based on non-precious metal catalysis (Fe, Co, Mn, Ni, etc.), (ii) the development of new strategies using non-precious metal-catalysts for the introduction of organo-fluorinine derivatives using N-heterocycles with one or more heteroatoms, (iii) newer reagents for fluorination, difluoromethylation, trifluoromethylation, or perfluoroalkylation of N-heteroarenes using different approaches, (iv) mechanistic studies on various catalytic transformations, as and when required, and (v) the synthetic applications of various bio-active organo-fluorine compounds, including post-synthetic drug derivatization, are discussed.

Copper-Catalyzed Direct Perfluoroalkylation of Heteroarenes

An efficient and broadly applicable process is reported for the copper-catalyzed direct perfluoroalkylation of C-H bonds in heteroarenes with commercially available perfluoroalkyl iodides. This reaction is based on a simple combination of copper(I) iodide and 1,10-phenanthroline enabling the easy reduction of perfluoroalkyl iodides to the corresponding radical species that add to a wide range of heteroarenes including benzofurans, benzothiophenes, (aza)indoles, furans and pyrroles. High levels of regioselectivity were obtained in all cases and the efficiency and robustness of this process was highlighted by the direct perfluoroalkylation of furan-containing peptides.

One-Pot Transformation of Hypervalent Iodines into Diversified Phenoxazine Analogues as Promising Photocatalysts

A facile and efficient quinoline-fused 4H-benzo[b][1,4]oxazine has been successfully fabricated through an oxidative O-arylation, Pd-catalyzed double N-arylation of 4-hydroxyquinoline derivatives and trivalent aryl iodides. Diversified fused heterocycles could be easily constructed in overall high isolated yields with great substrate scope. The afforded heteroatom-"doped" phenoxazine 3 demonstrated high molar absorptivities and excellent stability and redox reversibility. These phenoxazine analogues therefore could be utilized as promising catalysts in the photoredox catalyzed perfluoroalkylation of heteroarenes and photopromoted radical polymerization (OATRP).

Visible light-catalyzed fluoroalkylation reactions of free aniline derivatives

The electron-rich nature of aminoaromatic compounds and the electrophilic character of fluoroalkyl R_F radicals allow for a special match in substitution reactions. We herein present visible light photocatalyzed fluoroalkylation reactions of aniline derivatives, with a study of the reaction mechanisms. The examples evaluated make use of different photocatalysts, such as polypyridyl complexes of Ir or Ru transition metals, organic dyes such as Rose Bengal, phthalocyanine-metal organocatalysts, or visible-light activated complexes. Different visible light sources that span from the blue region of the electromagnetic spectrum to low power red light irradiation sources deliver the excited photocatalysts that ensue into the production of fluoroalkyl R_F radicals. In turn, many sources of R_F radicals can be employed, such as fluoroalkyl halides, Togni's reagents, Umemoto's reagent, etc. All these protocol variants demonstrate the expansion of the methodology and the versatility of photocatalytic techniques applied to a special family of organic compounds such as aminoaromatic substrates, which has been studied by different groups. Contributions from our own laboratory will be given.

Base-promoted perfluoroalkylation of rhodium(III) porphyrin complexes

A new family of rhodium porphyrin complexes bearing a primary, secondary or benzylic perfluoroalkyl ligand RhIII(btpp)RF [btpp = 5,10,15,20-tetrakis(4-tert-butylphenyl)porphyrinato dianion] has been successfully synthesized in good yields using commercially available perfluoroalkyl iodides RFI (RF = nC3F7, iC3F7, nC4F9, nC6F13, cC6F11, nC10F21 and C6F5CF2) and the air-stable precursor RhIII(btpp)Cl under basic conditions. Mechanistic investigations suggest a halogen atom transfer pathway with a rhodium(ii) porphyrin metalloradical.

Palladium-Catalyzed C2-Regioselective Perfluoroalkylation of the Free (NH)-Heteroarenes

A highly regioselective and atom-efficient strategy for the construction of fused free (NH) heteroarenes through a palladium-catalyzed perfluoroalkyl insertion reaction has been accomplished. This protocol employed multiple iodofluoroalkanes as practical and available perfluoroalkyl sources to provide an operationally simple and versatile route for the synthesis of perfluoroalkylated indoles. Moreover, indoles without the assistance of guide groups were utilized as substrates, achieving C(sp²)-H site-selective functionalization of indoles in yields up to 95%. Furthermore, this protocol was also used for late-stage C2 perfluoroalkylation of bioactive compounds such as auxin, tryptophan, and melatonin analogues.

Catalyst-free, visible-light-induced direct radical cross-coupling perfluoroalkylation of the imidazo[1,2-a]pyridines with perfluoroalkyl iodides

A mild and eco-friendly visible-light-induced direct radical cross-coupling perfluoroalkylation of the imidazo[1,2-a]pyridines with perfluoroalkyl iodides was established.