Azidofluoroalkylation of Alkenes with Simple Fluoroalkyl Iodides Enabled by Photoredox Catalysis

Photoinduced Copper-Catalyzed Asymmetric Three-Component Radical 1,2-Azidooxygenation of 1,3-Dienes

Radical-involved multicomponent difunctionalization of 1,3-dienes has recently emerged as a promising strategy for rapid synthesis of valuable allylic compounds in one-pot operation. However, the expansion of radical scope and enantiocontrol remain two major challenges. Herein, we describe an unprecedented photoinduced copper-catalyzed highly enantioselective three-component radical 1,2-azidooxygenation of 1,3-dienes with readily available azidobenziodazolone reagent and carboxylic acids. This mild protocol exhibits a broad substrate scope, high functional group tolerance, and exceptional control over chemo-, regio- and enantioselectivity, providing practical access to diverse valuable azidated chiral allylic esters. Mechanistic studies imply that the chiral copper complex is implicated as a bifunctional catalyst in both the photoredox catalyzed azidyl radical generation and enantioselective radical C-O cross-coupling.

Asymmetric Three-Component Radical Alkene Carboazidation by Direct Activation of Aliphatic C-H Bonds

Azide compounds are widely present in natural products and drug molecules, and their easy-to-transform characteristics make them widely used in the field of organic synthesis. The merging of transition-metal catalysis with radical chemistry offers a versatile platform for radical carboazidation of alkenes, allowing the rapid assembly of highly functionalized organic azides. However, the direct use of readily available hydrocarbon feedstocks as sp3-hybridized carbon radical precursors to participate in catalytic enantioselective carboazidation of alkenes remains a significant challenge that has yet to be addressed. Herein, we describe an iron-catalyzed asymmetric three-component radical carboazidation of electron-deficient alkenes by direct activation of aliphatic C-H bonds. This approach involves intermolecular hydrogen atom transfer between a hydrocarbon and an alkoxy/aryl carboxyl radical, leading to the formation of a carbon-centered radical. The resulting radical then reacts with electron-deficient alkenes to generate a new radical species that undergoes chiral iron-complex-mediated C-N3 bond coupling. An array of valuable chiral azides bearing a quaternary stereocenter were directly accessed from widely available chemical feedstocks, and their synthetic potential is further demonstrated through more facile transformations to give other valuable enantioenriched building blocks.

Copper-Catalyzed Selective Three-Component 1,2-Phosphonoazidation of 1,3-Dienes

We report a copper-catalyzed selective 1,2-phosphonoazidation of conjugated dienes. This three-component reaction is achieved by using readily available P(O)-H compounds and bench-stable NaN3. Salient features of this strategy include its mild reaction conditions, broad functional group tolerance, and high chemoselectivity and regioselectivity. Moreover, the compatibility with the late-stage functionalization of drug molecules, the potential for scalable production, and the feasibility of further modifications of the products underscore the practical utility of this protocol in synthetic applications.

Cu-Catalyzed Polychloromethylamination of Styrenes through C(sp3 )-H Bond Cleavage

A copper-catalyzed three-component coupling reaction has been developed allowing the rapid building of valuable complex highly functionalized β-polychloromethyl amines from simple styrenes, arylamines, and dichloromethane/chloroform. Using aryldiazonium salts as a radical initiator, a series of corresponding products are obtained with moderate to good yields under a carbon dioxide or nitrogen atmosphere (50 psi). In addition, good functional group tolerance can be observed.

Metal-Free Photochemical Imino-Alkylation of Alkenes with Bifunctional Oxime Esters

The concurrent installation of C-C and C-N bonds across alkene frameworks represents a powerful tool to prepare motifs that are ubiquitous in pharmaceuticals and bioactive compounds. To construct such prevalent bonds, most alkene difunctionalization methods demand the use of precious metals or activated alkenes. We report a metal-free, photochemically mediated imino-alkylation of electronically diverse alkenes to install both alkyl and iminyl groups in a highly efficient manner. The exceptionally mild reaction conditions, broad substrate scope, excellent functional group tolerance, and facile one-pot reaction protocol highlight the utility of this method to prepare privileged motifs from readily available alkene and acid feedstocks. One key and striking feature of this transformation is that an electrophilic trifluoromethyl radical is equally efficient with both electron-deficient and electron-rich alkenes. Additionally, dispersion-corrected density functional theory (DFT) and empirical investigations provide detailed mechanistic insight into this reaction.

Recent Advances in Photoinduced Perfluoroalkylation Using Perfluoroalkyl Halides as the Radical Precursors

Perfluoroalkylation is one of the most important methods for the introduction of multiple fluorine atoms into organic molecules in a single step. The use of photoinduced technology is a common strategy that uses the outstanding oxidation or reduction ability of a photo­redox catalyst in its excited state to generate perfluoroalkyl radicals from perfluoroalkyl halides. The perfluoroalkyl radicals thus obtained can undergo various subsequent reactions under mild conditions, such as ATRA reaction of alkenes, alkynes, and 1,n-enynes; carbo/heteroperfluoroalkylation of alkenes and isocyanides; and C–H/F perfluoroalkyl­ation. This allows the expedient incorporation of various perfluoroalkyl groups into the molecular motifs. Perfluorinated functional groups are still in demand in pharmaceutical and material sciences; this short review discusses recent advances in photoinduced perfluoroalkylation methodologies and technologies.

1 Introduction

2 Photocatalytic Perfluoroalkylation of Alkenes, Alkynes, and 1,n- Enynes

3 Photocatalytic Carboperfluoroalkylation or Heteroperfluoro­alkylation of Alkenes, Alkynes, Isocyanides, and Hydrazones

4 Photocatalytic ATRE Reactions of Alkenes with Perfluoroalkyl Halides­

5 Photocatalytic C–X (X = H, F) Bond Perfluoroalkylation

6 Continuous Flow Strategies in Photocatalytic Perfluoroalkylation

7 Conclusions

Radical 1,4/5-Amino Shift Enables Access to Fluoroalkyl-Containing Primary β(γ)-Aminoketones under Metal-Free Conditions

A novel radical 1,4/5-amino shift from the oxygen center of alkene-tethered diphenyl ketoxime ethers to the carbon center to achieve high value-added fluoroalkyl-containing primary β(γ)-amino-ketones is reported. Mechanism studies reveal that the migration is triggered by the alkene addition of fluoroalkyl radical derived from the electron donor-acceptor (EDA) complex of Togni's reagent II or fluoroalkyl iodides and quinuclidine, and involves a unique 5(6)-exo-trig cyclization of the carbon-centered radical onto the N-atom of ketoxime ethers followed by a cascade sequence of N-O bond cleavage and dehydrogenation. Notably, besides Togni's reagent II and fluoroalkyl iodides, this protocol is also compatible with other radical precursors to provide various functionalized primary aminoketones.

Palladium-Catalyzed Carbonylative Four-Component Synthesis of β-Perfluoroalkyl Amides

Transition-metal-catalyzed multicomponent carbonylation is one of the most efficient strategies to construct carbonyl-containing compounds. Herein, a palladium-catalyzed four-component perfluoroalkylation/aminocarbonylation of unactivated alkenes with perfluoroalkyl halides, and amines was developed. A wide range of substrates, including anilines, alkylamines, sulfonamides, and hydrazines are all suitable reaction partners for this catalyst system, resulting in various β-perfluoroalkyl amides with good functional-group tolerance and excellent chemoselectivity. Furthermore, not only alkyl olefins, but also aliphatic alkynes, and even alkyl allenes can all be employed. Notably, several medical and bioactive related molecules are compatible here as well.

Copper-Catalyzed Perfluoroalkylation of Alkynyl Bromides and Terminal Alkynes

A copper-catalyzed one-pot perfluoroalkylation of alkynyl bromides and terminal alkynes has been disclosed, and the corresponding perfluoroalkylated alkynes could be attained in good to excellent yields. The new straightforward transformation shows high efficiency (0.01-0.5 mol % catalyst loading), broad substrate scope, and remarkable functional group tolerance and provides a facile approach for useful application in life and material sciences.

Trifluoromethanesulfonyl azide as a bifunctional reagent for metal-free azidotrifluoromethylation of unactivated alkenes

Vicinal trifluoromethyl azides have widespread applications in organic synthesis and drug development. However, their preparation is generally limited to transition-metal-catalyzed three-component reactions. We report here a simple and metal-free method that rapidly provides these building blocks from abundant alkenes and trifluoromethanesulfonyl azide (N₃SO₂CF₃). This unprecedented two-component reaction employs readily available N₃SO₂CF₃ as a bifunctional reagent to concurrently incorporate both CF₃ and N₃ groups, which avoids the use of their expensive and low atom economic precursors. A wide range of functional groups, including bio-relevant heterocycles and amino acids, were tolerated. Application of this method was further demonstrated by scale-up synthesis (5 mmol), product derivatization to CF₃-containing medicinal chemistry motifs, as well as late-stage modification of natural product and drug derivatives.

A two-component and metal-free azidotrifluoromethylation of alkenes is realized using readily synthesized trifluoromethanesulfonyl azide (N₃SO₂CF₃) as a bifunctional reagent for both CF₃ and N₃ groups.

Cu-Catalyzed radical-triggered spirotricyclization of enediynes and enyne-nitriles for the synthesis of pentacyclic spiroindenes

A new copper-catalyzed radical-triggered fluoromethylation-spirotricyclization of enediyne- and enyne-nitrile-containing para-quinone methides (p-QMs) was reported for the first time, and used to produce a series of hitherto unreported pentacyclic spiroindenes.

Three-component photoredox 1,2-alkylamination of styrenes with alkanes and nitrogen nucleophiles via C(sp3)–H bond cleavage

A three-component photoredox 1,2-alkylamination of styrenes involving functionalization of C(sp3)–H bonds in alkyl halides instead of functionalization of C-halogen bonds is disclosed.

Visible light photocatalysis in the late-stage functionalization of pharmaceutically relevant compounds

The late stage functionalization (LSF) of complex biorelevant compounds is a powerful tool to speed up the identification of structure-activity relationships (SARs) and to optimize ADME profiles. To this end, visible-light photocatalysis offers unique opportunities to achieve smooth and clean functionalization of drugs by unlocking site-specific reactivities under generally mild reaction conditions. This review offers a critical assessment of current literature, pointing out the recent developments in the field while emphasizing the expected future progress and potential applications. Along with paragraphs discussing the visible-light photocatalytic synthetic protocols so far available for LSF of drugs and drug candidates, useful and readily accessible synoptic tables of such transformations, divided by functional groups, will be provided, thus enabling a useful, fast, and easy reference to them.

Metal-Catalyzed Spiroannulation-Fluoromethylfunctionaliztions of 1,5-Enynes for the Synthesis of Stereodefined (Z)-Spiroindenes

Two classes of new catalytic spiroannulation-fluormethylfunctionaliztions of para-quinone methide (p-QM)-containing 1,5-enynes have been established under redox-neutral conditions. Palladium-catalyzed spiroannulation-iododifluoromethylation with ethyl difluoroiodoacetate oriented completely stereoselective access to (Z)-spiroindenes and the latter included copper-catalyzed three-component spiroannulation-cyanotrifluoromethylation starting from Togni's reagent and trimethylsilanecarbonitrile (TMSCN). Both reaction pathways involve fluoroalkyl radical-triggered 1,6-addition/5-exo-dig annulation/metal radical cross-coupling/reductive elimination sequence, providing practical and stereoselective protocols for rapidly constructing cyclohexadienone-containing spiroindenes with generally good yields.

Transition Metal Catalyzed Azidation Reactions

A wide range of methodologies for the preparation of organic azides has been reported in the literature for many decades, due to their interest as building blocks for different transformations and their applications in biology as well as in materials science. More recently, with the spread of the use of transition metal-catalyzed reactions, new perspectives have also materialized in azidation processes, especially concerning the azidation of C–H bonds and direct difunctionalization of multiple carbon-carbon bonds. In this review, special emphasis will be placed on reactions involving substrates bearing a leaving group, hydroazidation reactions and azidation reactions that proceed with the formation of more than one bond. Further reactions for the preparation of allyl and vinyl azides as well as for azidations involving the opening of a ring complete the classification of the material.

Visible light photoredox alkylazidation of alkenes with sodium azide and heteroarenium salts: entry to azido-containing 1,4-dihydropyridines

A three-component alkene alkylazidation using sodium azide as the azido resource and heteroarenium salts as functionalized alkyl reagents for producing highly valuable 2-azido-1-(1,4-dihydropyridin-4-yl)-ethanes is described. This reaction allows the incorporation of both an azido group and a 1,4-dihydropyridin-4-yl group across C[double bond, length as m-dash]C bonds to construct two new bonds in a single reaction step, and represents a practical and mechanistically distinct alternative that harnesses an electrophilic heteroarenium ion to accomplish the alkene difunctionalization reaction.

Silver-Mediated Perfluoroalkylation of Terminal Alkynes with Perfluoroalkyl Iodides

The incorporation of a perfluoroalkyl group (R_F) into drug candidates has become an increasingly important strategy in drug molecule design. In this study, the silver-mediated perfluoroalkylation reaction based on the addition-elimination process of terminal alkynes which was initiated by a perfluoroalkyl radical to form a C(sp)-R_F bond has been developed. The reaction proceeds under mild conditions using readily available, low-cost perfluoroalkyl iodides as the sources of the R_F group. This method allows access to a variety of perfluoroalkylated alkynes.

Iron-Catalyzed Alkylazidation of 1,1-Disubstituted Alkenes with Diacylperoxides and TMSN3

An iron-catalyzed radical alkylazidation of electron-deficient alkenes is reported. Alkyl diacyl peroxides work as the alkyl source, and trimethylsilyl azide acts as the azido reservoir. This method features mild reaction conditions, wide substrate scope, and good functional group tolerance, providing a range of α-azido esters, an α-azido ketone, and an α-azido cyanide in high yields. These azides can be easily transferred into many kinds of amino acid derivatives.

Revealing the Iron-Catalyzed β-Methyl Scission of tert-Butoxyl Radicals via the Mechanistic Studies of Carboazidation of Alkenes

We describe here a mechanistic study of the iron-catalyzed carboazidation of alkenes involving an intriguing metal-assisted β-methyl scission process. Although t-BuO radical has frequently been observed in experiments, the β-methyl scission from a t-BuO radical into a methyl radical and acetone is still broadly believed to be thermodynamically spontaneous and difficult to control. An iron-catalyzed β-methyl scission of t-BuO is investigated in this work. Compared to a free t-BuO radical, the coordination at the iron atom reduces the activation energy for the scission from 9.3 to 3.9 ~ 5.2 kcal/mol. The low activation energy makes the iron-catalyzed β-methyl scission of t-BuO radicals almost an incomparably facile process and explains the selective formation of methyl radicals at low temperature in the presence of some iron catalysts. In addition, a radical relay process and an outer-sphere radical azidation process in the iron-catalyzed carboazidation of alkenes are suggested by density functional theory (DFT) calculations.

Intermolecular radical carboamination of alkenes

Vicinal alkene carboamination is a highly efficient and practical synthetic strategy for the straightforward preparation of diverse and valuable amine derivatives starting from simple compounds. During the last decade that approach has found continuous research interests and various practical methods have been developed using transition-metal catalysis. Driven by the renaissance of synthetic radical chemistry, intermolecular radical alkene carboamination comprising a C-C bond and a C-N bond forming step has been intensively investigated recently culminating in novel strategies and improved protocols which complement existing methodologies. Radical alkene carboamination can be achieved via three different reaction modes. Such cascades can proceed through N-radical addition to an alkene with subsequent C-C bond formation leading to 2,1-carboamination products. Alternatively, the C-C bond can be installed prior to the C-N bond via initial C-radical addition to the alkene with subsequent β-amination resulting in 1,2-carboamination. The third mode comprises initial single electron oxidation of the alkene to the corresponding alkene radical cation that gets trapped by an N-nucleophile and the cascade is terminated by radical C-C bond formation. In this review, the three different conceptual approaches will be discussed and examples from the recent literature will be presented. Further, the reader will get insights into the mechanism of the different transformations.

Dual Roles of tert-Butyl Nitrite in the Transition Metal- and External Oxidant-Free Trifluoromethyloximation of Alkenes

By employing tert-butyl nitrite as both nitrogen source and oxidant, the trifluoromethyloximation of alkenes proceeds smoothly in a free-radical process. The developed difunctionalization reaction enables practical and efficient synthesis of a wide range of α-CF₃ ketoximes in moderate yields with excellent regioselectivity. This method features the use of readily available and stable alkenes as substrates and inexpensive CF₃ SO₂ Na as a CF₃ reagent, no involvement of transition metals or external oxidant, and room-temperature conditions. Moreover, a scale-up of the reaction, further transformation of the products into various valuable CF₃ -containing compounds, and removal of the trifluoromethyl group are readily achieved.

Visible-Light-Driven Chlorotrifluoromethylative and Chlorotrichloromethylative Cyclizations of Enynes

Described herein is a visible-light-driven chlorotrifluoromethylative and chlorotrichloromethylative cyclization reaction to synthesize chlorotrifluoromethylated and chlorotrichloromethylated cyclic compounds. Visible-light photochemistry was utilized to generate trifluoromethyl and trichloromethyl radicals and trigger radical addition/cyclization/chlorination sequences. The use of terminal alkene-derived enynes enables the regioselective and stereoselective synthesis of chlorotrifluoromethylated and chlorotrichloromethylated pyrrolidines, piperidines, and cyclopentanes.

Progress and prospects in the use of photocatalysis for the synthesis of organofluorine compounds

Data on the synthesis of fluorinated organic compounds by photocatalysis are systematically considered and analyzed. The attention is focused on the mechanisms of photocatalytic reactions and the selectivity problem.

The bibliography includes 173 references.