Trifluoromethylthiolation-Based Bifunctionalization of Diazocarbonyl Compounds by Rhodium Catalysis

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Transition-metal-catalyzed C-H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XR_F, X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp²) and C(sp³) centers with SCF₃, SeCF₃, or OCH₂CF₃ groups among others, by C-H bond activation. The scope and limitations of these transformations are discussed in this review.

Preparation and Synthetic Applications of Five-to-Seven-Membered Cyclic α-Diazo Monocarbonyl Compounds

The reactivity of cyclic α-diazo monocarbonyl compounds differs from that of their acyclic counterparts. In this review, we summarize the current literature available on the synthesis and synthetic applications of three major classes of cyclic α-diazo monocarbonyl compounds: α-diazo ketones, α-diazo lactones and α-diazo lactams.

Trifluoromethylthiolation of Hindered α-Bromoamides with Nucleophilic Trifluoromethylthiolating Reagents

General methods have not been previously developed for the synthesis of sterically hindered α-SCF₃-substituted carbonyl compounds using nucleophilic trifluoromethylthiolating reagents. Thus, we herein report sp³C-SCF₃ bond formation in hindered α-bromoamides containing 3-bromo-oxindoles and linear α-bromoamides using CuSCF₃ or AgSCF₃ under mild conditions to access sterically hindered α-SCF₃-substituted amides. This transformation is applicable to not only 3-SCF₃-substituted oxindoles but also primary and secondary amides and reveals a broad functional group tolerance. This method will benefit the fields of medicinal and agricultural chemistry.

Diazocarbonyl Compounds in Organofluorine Chemistry

Diazocarbonyl compounds are useful substrates in di- and trifunctionalization reactions based on F/CF3/SCF3 introduction. In the presented reactions, various electrophilic F/CF3/SCF3-transfer reagents were used. The majority of the reactions were based on rhodium catalysis and the application of various oxygen nucleophiles, such as alcohols, cyclic/acyclic ethers, and carboxylic acids. The oxyfluorination reactions were further developed to provide a new fluorine-18 labeling method. Density functional theory (DFT) modeling studies were performed to get a deeper mechanistic understanding of these reactions. These DFT modeling studies indicated that the catalytic reactions proceed through formation of rhodium carbene and oxonium ylide intermediates. The oxonium ylides undergo tautomerization to enol ether type species that subsequently react with the electrophilic F/CF3/SCF3-transfer reagents. We also present an arylation–trifluoromethylthiolation reaction for simultaneous introduction of C–SCF3 and C–C bonds into diazocarbonyl compounds. This reaction does not proceed by rhodium catalysis, but follows a Hooz-type mechanism.

1 Introduction

2 Diazocarbonyl Compounds: Versatile Substrates in Organic ­Synthesis

3 Fluorination, Trifluoromethylation, and Trifluoromethylthiolation of Diazo Substrates

3.1 Metal-Free Reactions

3.2 Metal-Catalyzed Reactions with Nucleophilic Reagents

3.3 Metal-Catalyzed Reactions with Electrophilic Reagents

4 Oxyfluorination Reactions

4.1 Fluorobenziodoxole as a Fluorine Source

4.2 [18F]Fluorobenziodoxole as a Fluorine Source for Radiolabeling

4.3 Oxyfluorination with NFSI

5 Oxytrifluoromethylation

6 Oxytrifluoromethylthiolation

7 Arylation–Trifluoromethylthiolation Reaction

8 Conclusions and Outlook

Radical-Promoted Distal C-H Functionalization of C(sp3 ) Centers with Fluorinated Moieties

Due to their unique properties, fluorinated scaffolds are pivotal compounds in pharmaceuticals, agrochemicals, and materials science. Over the last years, the development of versatile strategies for the selective synthesis of fluorinated molecules by direct C-H bond functionalization has attracted a lot of attention. In particular, the design of novel transformations based on a radical process was a bottleneck for distal C-H functionalization reactions, offering synthetic solutions for the selective introduction of fluorinated groups. This Minireview highlights the major contributions in this blossoming field. The development of new methodologies for the remote functionalization of aliphatic derivatives with various fluorinated groups based on a 1,5-hydrogen atom transfer process and a β-fragmentation reaction will be showcased and discussed.

Recent Perspectives on Rearrangement Reactions of Ylides via Carbene Transfer Reactions

Among the available methods to increase the molecular complexity, sigmatropic rearrangements occupy a distinct position in organic synthesis. Despite being known for over a century sigmatropic rearrangement reactions of ylides via carbene transfer reaction have only recently come of age. Most of the ylide mediated rearrangement processes involve rupture of a σ-bond and formation of a new bond between π-bond and negatively charged atom followed by simultaneous redistribution of π-electrons. This minireview describes the advances in this research area made in recent years, which now opens up metal-catalyzed enantioselective sigmatropic rearrangement reactions, metal-free photochemical rearrangement reactions and novel reaction pathways that can be accessed via ylide intermediates.

Three-Component Reaction for the Synthesis of Highly Functionalized Propargyl Ethers

Multicomponent reactions provide efficient means to access molecular complexity. Herein, we report a copper-catalyzed three-component reaction of diazo compounds, alcohols and ethynyl benziodoxole (EBX) reagents for the synthesis of propargyl ethers. Extensive variations of the three partners of the reaction is possible, leading to highly functionalized and structurally diverse products under mild conditions. Alkynylation of a copper ylide intermediate is postulated as key step for this transformation.

An asymmetric hydrocyanation/Michael reaction of α-diazoacetates via Cu(i)/chiral guanidine catalysis

An asymmetric one-pot hydrocyanation/Michael reaction of α-aryl diazoacetates with trimethylsilyl cyanide, tert-butanol, and N-phenylmaleimides has been realized using a chiral guanidinium salt/CuBr catalyst.

Practical and regioselective halo-trifluoromethylthiolation of sulfur ylides

A H2O mediated practical and highly regioselective chloro- and bromo-trifluoromethylthiolation of sulfur ylides is reported using a difunctionalization strategy. In the reaction sequence, sulfur ylides presumably react with an electrophilic trifluoromethylthiolating reagent to generate an α-SCF3 substituted sulfonium salt intermediate, which then undergoes a substitution with nucleophilic halogens.

Photochemical fluoro-amino etherification reactions of aryldiazoacetates with NFSI under stoichiometric conditions

A photochemical three-component reaction is reported that allows the introduction of fluorine and a short polyether side chain in high efficiency under metal-free conditions.

Trifluoromethylthiolation-arylation of diazocarbonyl compounds by modified Hooz multicomponent coupling

A new Zn-mediated trifluoromethylthiolation-based bifunctionalization reaction is developed. In this process, simultaneous C-SCF3 and C-C bond formation takes place in a multicomponent reaction, in which an aryl and a SCF3 group arise from different reagents. Our studies show that the reaction mechanism is similar to the Hooz multicomponent coupling. The process involves in situ generation of BAr3, which reacts with a diazocarbonyl compound, and the reaction is terminated by an electrophilic SCF3 transfer. The reaction can also be extended to fluorination based bifunctionalization which proceeds with somewhat lower yield than the analogous trifluoromethylthiolation reaction.

Visible-light-induced radical trifluoromethylthiolation of N-(o-cyanobiaryl)acrylamides

An efficient and general visible-light-mediated trifluoromethylthiolation of N-(o-cyanobiaryl)acrylamides has been successfully accomplished using N-trifluoromethylthiosaccharin as an effective source of SCF3 radicals. The reaction was proposed to proceed via a domino radical trifluoromethylthiolation/cyano insertion/cyclization to afford the corresponding SCF3-containing ring-fused phenanthridine derivatives in moderate to good yields.

Use of ArSO2SRf reagents: an efficient tool for the introduction of SRf moieties

In recent years, a renewal of interest was shown to the quest for new synthetic solutions to directly introduce emergent fluorinated groups (SRf) onto molecules. In this context, a new generation of reagents (ArSO2SRf) as efficient sources of SCF3, SCF2H and more generally SRf groups, was designed. Hence, potent solutions were developed for the synthesis of SRf-containing molecules, compounds of interest for drug and agrochemical research. This review highlights the recent advances made in the synthesis and the use of this new class of reagents, considerably extending the portfolio of tools for the direct introduction of SRf moieties.

Rhodium-mediated 18F-oxyfluorination of diazoketones using a fluorine-18-containing hypervalent iodine reagent

α-[¹⁸F]Fluoro ethers were obtained from diazocarbonyl compounds using a hypervalent iodine based fluorine-18 reagent.

Nickel-Catalyzed Carbonylative Synthesis of Functionalized Alkyl Iodides

Functionalized alkyl iodides are important compounds in organic chemistry and biology. In this communication, we developed an interesting nickel-catalyzed carbonylative synthesis of functionalized alkyl iodides from aryl iodides and ethers. With Mo(CO)₆ as the solid CO source, both cyclic and acyclic ethers were activated, which is also a challenging topic in organic synthesis. Functionalized alkyl iodides were prepared in moderate to excellent yields with outstanding functional group tolerance. Besides the high value of the obtained products, all the atoms from the starting materials were incorporated in the final products and the reaction had high atom efficiency as well.

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Nickel-catalyzed carbonylative synthesis of functionalized alkyl iodides

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With Mo(CO)₆ as the solid CO source, carbonylative ether activation

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Good yields of functionalized alkyl iodides