Copper‐Catalysed Decarboxylative Trifluoromethylation of β‐Ketoacids

An efficient method for Cu‐catalyzed decarboxylative trifluoromethylation of β ‐ketoacids to achieve α ‐trifluoromethyl ketones was developed. A wide variety of synthetically useful α ‐trifluoromethyl ketones were obtained in modest to good yields under mild reaction conditions. The present method also exhibits good functional‐group compatibility.     

Iron‐Catalyzed Decarboxylation of Trifluoroacetate and Its Application to the Synthesis of Trifluoromethyl Thioethers

Nucleophilic CF₃ has been generated by decarboxylation of potassium trifluoroacetate, arguably the most easy‐to‐handle, inexpensive, and sustainable source of trifluoromethyl groups. Simple iron(II) chloride catalyzes the decarboxylation as well as a subsequent trifluoromethylation of organothiocyanates, resulting in a straightforward synthesis of trifluoromethyl thioethers. The KCN byproduct is absorbed by iron(II) with formation of nontoxic potassium hexacyanoferrate. An analogous trifluoromethylation of aldehydes with trifluoroacetate underlines the synthetic potential of such iron‐catalyzed decarboxylative trifluoromethylations.     

Trifluoromethylation of Alkyl Radicals: Breakthrough and Challenges†

Trifluoromethylation of alkyl radicals is emerging as a powerful tool for C(sp³)–CF₃ bond formations. Based on the hypothesis of CF₃ group transfer from Cu(II)–CF₃ to alkyl radicals, a number of trifluoromethylation reactions have been developed, including trifluoromethylation of alkyl halides, decarboxylative trifluoromethylation of aliphatic carboxylic acids, C(sp³)–H trifluoromethylation, amino‐ and carbo‐trifluoromethylation of alkenes, etc. Challenges in this intriguing field are also discussed.     

Silver‐Mediated N‐Trifluoromethylation of Amides and Peptides

We report herein the direct N‐trifluoromethylation of N‐H amides. Promoted by AgOTf and 2‐fluoropyridine, the reaction of a variety of amides with Selectfluor, TMSCF₃ and CsF proceeds smoothly at room temperature leading to the corresponding N‐trifluoromethylated products in satisfactory yields. The protocol is also applicable to amino acid derivatives, resulting in efficient and chemoselective N‐trifluoromethylation of di‐ and tri‐peptides with retention of configuration. A mechanism involving reductive elimination of Ag(III) intermediates to form N—CF₃ bonds is proposed.     

Rhodium‐Catalyzed Geminal Oxyfluorination and Oxytrifluoro‐Methylation of Diazocarbonyl Compounds

A new reaction for the rhodium‐catalyzed geminal‐difunctionalization‐based fluorination is presented. The substrates are aromatic and aliphatic diazocarbonyl compounds. As the fluorine source a stable and easily accessible benziodoxole reagent was used. A variety of alcohol, phenol, and carboxylic acid reagents were employed to introduce the second functionality. The reaction was extended to trifluoromethylation using a benziodoxolon reagent. The fluorination and trifluoromethylation reactions probably proceed by a rhodium‐containing onium ylide type intermediate, which is trapped by either the F or CF₃ electrophiles.     

Pd‐Catalyzed Decarboxylative Cross‐Coupling of 2‐Carboxyazine N‐Oxides with Various (Hetero)aryl Halides

Decarboxylative cross‐coupling reactions of substituted 2‐carboxyazine N‐oxides, with a variety of (hetero)aryl halides, by bimetallic Pd⁰/Cu^I and Pd⁰/Ag^I catalysis are reported. Two possible pathways, a conventional bimetallic‐catalyzed decarboxylative arylation, as well as a protodecarboxylative/direct C?H arylation sequence have been considered. These methods provide the first general decarboxylative arylation methodology for the 2‐carboxyazine series.     

Palladium‐Catalyzed Decarboxylative γ‐Arylation for the Synthesis of Tetrasubstituted Chiral Allenes

An enantiospecific palladium‐catalyzed decarboxylative coupling of acyclic β,γ‐alkynoic acids with various aryl iodides to chiral tetrasubstituted allenes is described. The coupling reaction comprises a decarboxylative γ‐palladation of α,α‐disubstituted carboxylic acids to provide the tetrasubstituted allenes with complete point‐to‐axial chirality transfer in excellent yields.     

Synthesis of homochiral 2‐C‐trifluoromethyl D‐and L‐ribose via trifluoromethylation of pentopyranosid‐2‐uloses

Efficient syntheses of 2‐C‐trifluoromethyl D‐ and L‐ribose and some O‐glycosides via trifluoromethylation of D‐ and L‐3,4‐O‐isopropylidene‐β‐erythro‐pentopyranosid‐2‐ulose with Ruppert's reagent are described.     

Asymmetric Decarboxylative 1,4‐Addition of Malonic Acid Half Thioesters to Vinyl Sulfones: Highly Enantioselective Synthesis of 3‐Monofluoromethyl‐3‐Arylpropanoic Esters

An asymmetric decarboxylative 1,4‐addition of malonic acid half thioesters (MAHTs) to 2‐aryl‐substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97 % ee). In view of tuning pK_a values, a quinine‐based benzyl‐substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3‐monofluorinated analogues of 3‐methyl indanone and (+)‐turmerone has been accomplished from decarboxylative 1,4‐addition adducts with satisfactory results.     

Monofluorination and Trifluoromethylation of BODIPY Dyes for Prolonged Single‐Molecule Detection

Electrophilic monofluorination with Selectfluor and nucleophilic trifluoromethylation with the Ruppert–Prakesh reagent of dimethyl‐, tetramethyl‐ and pentamethyl‐substituted boron dipyrromethenes (BODIPY) are investigated. Monofluorinated dyes are synthesized with low yields (<30 %), however trifluoromethyl derivatives are obtained in moderate to high yields (≈40–90 %). All compounds are characterized by steady‐state and time‐resolved fluorescence spectroscopy, the photostability is investigated with fluorescence correlation spectroscopy (FCS) and total internal reflection fluorescence microscopy (TIRF). Monofluorination hardly affects the spectroscopic parameters of the unsubstituted parent compounds, but distinctly enhances the photostability, whereas trifluoromethylation leads to a hypsochromic shift by up to 17 nm in both absorption and emission, slightly enhanced intersystem crossing, and higher photostability. Further development of soft fluorination and trifluoromethylation methods is therefore highly desired.     

Palladium‐Catalyzed Aza‐Wittig‐Type Condensation of Isoxazol‐5(4H)‐ones with Aldehydes

This paper describes the development of a palladium‐catalyzed decarboxylative inter‐ and intramolecular condensation reaction of isoxazol‐5(4 H)‐ones with carbonyl compounds in the presence of PPh₃, giving various 2‐azabuta‐1,3‐dienes or pyrroles in moderate to high yields.     

Copper‐Mediated Decarboxylative Coupling of Benzamides with ortho‐Nitrobenzoic Acids by Directed C−H Cleavage

A copper‐mediated decarboxylative coupling of benzamides with ortho ‐nitrobenzoic acids by 8‐aminoquinoline‐directed C−H cleavage has been developed. This reaction proceeds smoothly with only a copper salt to produce the corresponding biaryl compounds in good yields. The products can be easily transformed into various nitrogen‐containing heterocyclic compounds. Moreover, the combination of copper and a suitable base promotes a decarboxylative C−H arylation and cyclization sequence to deliver phenanthridinone derivatives in one pot.     

NHC‐Catalyzed Electrophilic Trifluoromethylation: Efficient Synthesis of γ‐Trifluoromethyl α,β‐Unsaturated Esters

Described herein is a highly regioselective and efficient N‐heterocyclic‐carbene‐catalyzed γ‐trifluoromethylation of vinylogous enolates. Control experiments and DFT calculations provided important insight into the reaction mechanism.     

Nickel‐Mediated Trifluoromethylation of Phenol Derivatives by Aryl C−O Bond Activation

The increasing pharmaceutical importance of trifluoromethylarenes has stimulated the development of more efficient trifluoromethylation reactions. Tremendous efforts have focused on copper‐ and palladium‐mediated/catalyzed trifluoromethylation of aryl halides. In contrast, no general method exists for the conversion of widely available inert electrophiles, such as phenol derivatives, into the corresponding trifluoromethylated arenes. Reported herein is a practical nickel‐mediated trifluoromethylation of phenol derivatives with readily available trimethyl(trifluoromethyl)silane (TMSCF₃). The strategy relies on PMe₃‐promoted oxidative addition and transmetalation, and CCl₃CN‐induced reductive elimination. The broad utility of this transformation has been demonstrated through the direct incorporation of trifluoromethyl into aromatic and heteroaromatic systems, including biorelevant compounds.     

Metal‐Free,Initiator‐Free Graphene Oxide‐Catalyzed Trifluoromethylation of Arenes

The direct C−H trifluoromethylation of arenes catalyzed by graphene oxide (GO) under safe conditions is described. This strategy is metal‐free, initiator‐free, safe, and scalable. It employs a readily available CF₃ source and the reaction can be easily controlled to obtain a mono‐trifluorinated product. This method opens a new avenue for GO‐catalyzed chemistry.     

Trifluoromethanesulfonic Anhydride as a Low‐Cost and Versatile Trifluoromethylation Reagent

A large number of reagents have been developed for the synthesis of trifluoromethylated compounds. However, an ongoing challenge in trifluoromethylation reaction is the use of less expensive and practical trifluoromethyl sources. We report herein the unprecedented direct trifluoromethylation of (hetero)arenes using trifluoromethanesulfonic anhydride as a radical trifluoromethylation reagent by merging photoredox catalysis and pyridine activation. Furthermore, introduction of both the CF₃ and OTf groups of the trifluoromethanesulfonic anhydride into internal alkynes to access tetrasubstituted trifluoromethylated alkenes was achieved. Since trifluoromethanesulfonic anhydride is a low‐cost and abundant chemical, this method provides a cost‐efficient and practical route to trifluoromethylated compounds.     

Copper‐Catalyzed Trifluoromethylation of Internal Olefinic CH Bonds: Efficient Routes to Trifluoromethylated Tetrasubstituted Olefins and N‐Heterocycles

The functionalization of internal olefins has been a challenging task in organic synthesis. Efficient Cu^II‐catalyzed trifluoromethylation of internal olefins, that is, α‐oxoketene dithioacetals, has been achieved by using Cu(OH)₂ as a catalyst and TMSCF₃ as a trifluoromethylating reagent. The push–pull effect from the polarized olefin substrates facilitates the internal olefinic C?H trifluoromethylation. Cyclic and acyclic dithioalkyl α‐oxoketene acetals were used as the substrates and various substituents were tolerated. The internal olefinic C?H bond cleavage was not involved in the rate‐determining step, and a mechanism that involves radicals is proposed based on a TEMPO‐quenching experiment of the trifluoromethylation reaction. Further derivatization of the resultant CF₃ olefins led to multifunctionalized tetrasubstituted CF₃ olefins and trifluoromethylated N‐heterocycles.     

A Free‐Radical‐Promoted Stereospecific Decarboxylative Silylation of α,β‐Unsaturated Acids with Silanes

A stereospecific decarboxylative silylation of acrylic and propiolic acids with silanes was developed. This reaction represents the first example of decarboxylative C? Si bond formation and provides an efficient and convenient approach to various synthetically useful alkenyl and alkynyl organosilicon compounds through the reaction of α,β‐unsaturated acids with silanes. Spin‐trapping and EPR experiments support a radical addition/elimination process.     

Copper‐Catalyzed Highly Stereoselective Trifluoromethylation and Difluoroalkylation of Secondary Propargyl Sulfonates

It is challenging to stereoselectively introduce a trifluoromethyl group (CF₃) into organic molecules. To date, only limited strategies involving direct asymmetric trifluoromethylation have been reported. Herein, we describe a new strategy for direct asymmetric trifluoromethylation through the copper‐catalyzed stereospecific trifluoromethylation of optically active secondary propargyl sulfonates. The reaction enables propargylic trifluoromethylation with high regioselectivity and stereoselectivity. The reaction could also be extended to stereospecific propargylic difluoroalkylation. Transformations of the resulting enantiomerically enriched fluoroalkylated alkynes led to a variety of chiral fluoroalkylated compounds, thus providing a useful protocol for applications in the synthesis of fluorinated complexes.     

Silver‐Mediated Oxidative Trifluoromethylation of Phenols: Direct Synthesis of Aryl Trifluoromethyl Ethers

Aryl trifluoromethyl ethers (ArOCF₃) are prevalent in pharmaceuticals, agrochemicals, and materials. However, methods for the general and efficient synthesis of these compounds are extremely underdeveloped and limited. Herein, we describe a highly efficient and general procedure for the direct O‐trifluoromethylation of unprotected phenols through a silver‐mediated cross‐coupling reaction using CF₃SiMe₃ as the CF₃ source and exogenous oxidants. This novel oxidative trifluoromethylation provides access to a wide range of aryl trifluoromethyl ethers from simple phenols. The mild process was also applied to the late‐stage trifluoromethylation of a medicinally relevant compound.