Trifluoromethylthiolation of Diazo Compounds through Copper Carbene Migratory Insertion

Copper-Catalyzed Enantioselective C(sp3 )-SCF3 Coupling of Carbon-Centered Benzyl Radicals with (Me4 N)SCF3

In contrast with the well-established C(sp2 )-SCF3 cross-coupling to forge the Ar-SCF3 bond, the corresponding enantioselective coupling of readily available alkyl electrophiles to forge chiral C(sp3 )-SCF3 bond has remained largely unexplored. We herein disclose a copper-catalyzed enantioselective radical C(sp3 )-SCF3 coupling of a range of secondary/tertiary benzyl radicals with the easily available (Me4 N)SCF3 reagent. The key to the success lies in the utilization of chiral phosphino-oxazoline-derived anionic N,N,P-ligands through tuning electronic and steric effects for the simultaneous control of the reaction initiation and enantioselectivity. This strategy can successfully realize two types of asymmetric radical reactions, including enantioconvergent C(sp3 )-SCF3 cross-coupling of racemic benzyl halides and three-component 1,2-carbotrifluoromethylthiolation of arylated alkenes under mild reaction conditions. It therefore provides a highly flexible platform for the rapid assembly of an array of enantioenriched SCF3 -containing molecules of interest in organic synthesis and medicinal chemistry.

Visible Light-Driven α-Diazoketones as Denitrogenated Synthons: Synthesis of Fluorinated N-Heterocycles via Multicomponent Cyclization Reactions

We disclose herein an efficient photochemical formal [3+2+1] annulation strategy for the transformation of diazocarbonyl compounds into various fluorinated nitrogen-containing heterocycles. This transformation is characterized by reacting fluoroalkyl radicals with α-diazoketones, which are used as infrequent denitrogenated synthons under visible light. Moreover, a wide range of N-heterocycles containing precious CF₃ and perfluoroalkylated groups are constructed in moderate to good yields. Notably, this photochemical strategy may provide a fruitful path for the synthesis of complex organofluorides via diazo/fluorine/radical chemistry.

Visible-Light-Induced Trifluoromethylsulfonylation Reaction of Diazo Compounds Enabled by Manganese Catalysis

A visible-light-induced trifluoromethylsulfonylation reaction of diazo compounds is herein reported. This developed synthetic method captures the relatively rare trifluoromethyl sulfone radicals via coordination to the Mn(acac)₃ catalyst, delivering the corresponding α-trifluoromethyl sulfone esters in good to moderate yields (up to 82%). This protocol exhibits broad substrate scope and is easily carried out under mild reaction conditions. Furthermore, a plausible mechanism of the reaction was investigated through DFT calculations.

Application of Aromatic Substituted 2,2,2-Trifluoro Diazoethanes in Organic Reactions

Abstract:

This review provides an overview of metal-, nonmetal-, light-, or catalyst free-promoting reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with organic molecules for the synthesis of trifluoromethyl-substituted compounds. Several approaches will be reviewed and divided into (i) copper-, iron-, Trop(BF4)-, B(C6F5)3-, light-, or rhodium-promoted reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with silanes, amines, mercaptans, phosphonates, p-cyanophenol, benzoic acid, diphenylphosphinic acid, boranes and nBu3SnH, (ii) rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with amides and phenylhydroxylamine, (iii) copper-, rhodium-, silver-, and light-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkynes, (iv) palladium-, copper-, rhodium- and iron-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with alkenes, (v) BF3·OEt2-, copper-, tin- or TBAB-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with HF·Py, (difluoroiodo)toluene (p-TolIF2), TMSCF3, AgSCF3, TMSCF2Br or 1,3-dicarbonyl compounds, (vi) palladium-, copper-, gold/silver- or rhodium-catalyzed reactions of aromatic substituted 2,2,2-trifluoro diazoethanes with indoles, benzene compounds or pyridines, and (vii) palladium-catalyzed reaction of aromatic substituted 2,2,2-trifluoro diazoethanes with benzyl or allyl bromides.

Emerging Applications of Aryl Trifluoromethyl Diazoalkanes and Diazirines in Synthetic Transformations

Aryl trifluoromethyl diazoalkanes and diazirines have become unique as reactants in synthetic methodology. As privileged compounds containing CF₃ groups and ease of synthetic access, aryl trifluoromethyl diazoalkanes and diazirines have been highlighted for their versatility in applications toward a wide range of synthetic transformations. This Perspective highlights the synthetic applications of these reactants as precursors of stabilized metal carbenes, i.e., donor-acceptor-substituted ones.

Water-promoted regio-selective trifluoromethylation of vinyl conjugated diazoacetates

An efficient trifluoromethylation reaction of vinyldiazoacetates under mild reaction conditions was depicted.

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

Perfluoroalkylation of Thiosulfonates: Synthesis of Perfluoroalkyl Sulfides

A practical synthesis of perfluoroalkyl sulfides is described. The method employs stable and readily accessible thiosulfonates as new electrophiles with commercial nucleophilic perfluoroalkylating reagents. The mild reaction conditions allow access to a wide variety of both aryl- and alkyl-substituted perfluoroalkyl sulfides amenable to pharmaceutical development. Furthermore, the reaction operation is straightforward, odorless, does not produce toxic wastes, and, therefore should appeal to practitioners in industrial-scale productions.

Synthesis of α-Trifluoromethylthio-α,β-Unsaturated Carbonyl Compounds by DABCO-Mediated Electrophilic Trifluoromethylthiolation with N-SCF3-Dibenzenesulfonimide

A DABCO-mediated electrophilic α-trifluoromethylthiolation of α,β-unsaturated carbonyl compounds comprising no β-substituents has been achieved using N-trifluoromethylthio-dibenzenesulfonimide as the SCF₃ source. The direct trifluoromethylthiolation provides the corresponding α-trifluoromethylthio-α,β-unsaturated carbonyl products in good yields (up to 88%). Furthermore, the vinyl group in the α-trifluoromethylthio-α,β-unsaturated carbonyl product was successfully transformed into diverse functional groups in good to excellent yields (70-95%) by reactions such as epoxidation, aziridination, hydrocyanation, and hydrogenation.

Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale

The Cu-catalyzed reaction of substituted α-diazoesters with fluoride gives α-fluoroesters with ee values of up to 95 %, provided that chiral indane-derived bis(oxazoline) ligands are used that carry bulky benzyl substituents at the bridge and moderately bulky isopropyl groups on their core. The apparently homogeneous solution of CsF in C6 F6 /hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH2 Cl2 /HFIP also provides good results. DFT studies suggest that fluoride initially attacks the Cu- rather than the C-atom of the transient donor/acceptor carbene intermediate. This unusual step is followed by 1,2-fluoride shift; for this migratory insertion to occur, the carbene must rotate about the Cu-C bond to ensure orbital overlap. The directionality of this rotatory movement within the C2 -symmetric binding site determines the sense of induction. This model is in excellent accord with the absolute configuration of the resulting product as determined by X-ray diffraction using single crystals of this a priori wax-like material grown by capillary crystallization.

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.

Formal α-trifluoromethylthiolation of carboxylic acid derivatives via N-acyl pyrazoles

A direct and general one-pot approach to α-trifluoromethylthiolated amides, esters and carboxylic acids has been successfully developed under mild, catalytic and metal-free conditions.

gem-Difluoroallylation of Aryl Diazoesters via Catalyst-Free, Blue-Light-Mediated Formal Doyle-Kirmse Reaction

A first example of low-energy blue-light-mediated formal Doyle-Kirmse reaction for gem-difluoroallylation of aryl diazoesters has been developed. A variety of highly functionalized gem-difluoroallyl containing esters bearing transformable sulfur and bromine groups were efficiently assembled with broad substrate scope under mild, catalyst-free, and additive-free conditions. The reaction represents a practical and environmentally friendly approach for C-CF₂ bond formation based on rearrangement strategy, which will find potential applications among drug discovery and development.

Late stage trifluoromethylthiolation strategies for organic compounds

Substitution by the CF3S group allows for an increase in lipophilicity and electron-withdrawing properties along with an improvement in the bioavailability of medicinal targets; consequently, the late stage introduction of CF3S moieties into medicinal scaffolds is a sought-after strategy in synthetic organic chemistry. Different newly-developed electrophilic and nucleophilic reagents are used to effect the trifluoromethylthiolation of (hetero)aromatic compounds, aliphatic compounds (alkyl, alkenyl, alkynyl substrates), the trifluoromethylthiolation at the α- and β-carbonyl positions, and heteroatoms (N- and S-). Such reactions can involve homolytic substitutions, or functional-group substitutions (ipso). Addition reactions of electrophilic reagents to double and triple bonds followed by ring-cyclizations will be shown to yield relevant CF3S-substituted heteroaromatic compounds with relevant pharmacological action.

Nucleophilic trifluoromethylthiolation of bromoalkynones with AgSCF3: C(sp)–SCF3 bond formation towards ynonyl trifluoromethyl sulfides

C(sp)–SCF₃ bond formation via the AgSCF₃ mediated nucleophilic trifluoromethylthiolation of bromoalkynones, delivering various ynonyl trifluoromethyl sulfides in high yields.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

When diazo compounds meet with organoboron compounds

Transition-metal free reactions of diazo compounds with organoboron compounds provide some unique approaches for the formation of C–C, C–B and C–Si bonds. With N-tosylhydrazones as the precursors for non-stabilized diazo compound, this type of reaction becomes practically useful in organic synthesis. Transition-metal-free synthetic methodologies for borylation, gem-diborylation, gem-silylborylation arylation, 2,2,2-trifluoroethylation and gem-difluorovinylation have been successfully developed.

Tandem trifluoromethylthiolation/aryl migration of aryl alkynoates to trifluoromethylthiolated alkenes

The oxidative trifluoromethylthiolation of aryl alkynoates with AgSCF₃ provided a new access to trifluoromethylthiolated alkenes.

Transition metal-free direct trifluoromethylthiolation of indoles using trifluoromethanesulfonyl chloride in the presence of triphenylphosphine

A novel triphenylphosphine-mediated direct trifluoromethylthiolation of indole derivatives using trifluoromethanesulfonyl chloride as the SCF₃ source was developed.

Regioselective ortho-trifluoromethylthiolation of 2-arylbenzo[d]thiazole via tandem substrate-assisted C-H iodination and trifluoromethylthiolation

A mild and efficient tandem benzo[d]thiazole directed C-H iodination and trifluoromethylthiolation for the synthesis of ortho-trifluoromethylthiolated 2-arylbenzo[d]thiazoles have been developed using AgSCF3 as a coupling partner. The reaction exhibits a diverse array of functional group tolerance giving the desired products in good to excellent yields. Regioselective trifluoromethylthiolation was observed at the less sterically hindered site when the phenyl ring of the substrate possesses a methyl group at its meta position.