Chiral Brønsted acid-catalyzed diastereo- and enantioselective synthesis of CF3-substituted aziridines

CsF-Mediated Reaction of Trifluorodiazoethane with 3-Nitroindoles Enables Access to Trifluoromethylpyrazolo[4,3-b]indoles

A mild and metal-free strategy for the construction of trifluoromethylated pyrazolo[4,3-b]indoles through the reaction of N-substituted 3-nitroindoles with trifluorodiazoethane is reported. This operationally simple transformation involves a [3 + 2] cycloaddition of trifluorodiazoethane with 3-nitroindole, followed by the elimination of the nitro group to furnish pyrazole-fused indoles. The synthetic utility of this method is further demonstrated by applying it to other heterocycles, such as 3-nitrobenzothiophene and 2-nitrobenzofuran.

Ag-Catalyzed Annulation of o-Alkynylaryl Aldehydes, Amines, and Diazo Compounds: Construction of Trifluoromethyl- and Cyano-Functionalized Benzo[d]azepines

A Ag-catalyzed three-component annulation protocol, which uses o-alkynylaryl aldehydes, amines, and trifluorodiazoethane or diazoacetonitrile, to forge a new class of trifluoromethyl- and cyano-functionalized benzo[d]azepine is presented in this Letter. The key transformations involved in this reaction are the transient formation of the isoquinolinium intermediate and the subsequent ring-expansive addition of in situ-formed silver trifluorodiazoethylide to this intermediate. The practicality of this protocol is illustrated by realizing access to a wide range of densely functionalized benzo[d]azepines.

Metal-free [2 + 1 + 3] Cycloaddition of Trifluoroacetaldehyde N-Sulfonylhydrazones with Hexahydro-1,3,5-triazines Leading to Trifluoromethylated 2,3,4,5-Tetrahydro-1,2,4-triazines

A transition-metal-free [2 + 1 + 3] cycloaddition of trifluoroacetaldehyde N-sulfonylhydrazone and hexahydro-1,3,5-triazine was described. This operationally simple protocol provides a general synthesis of diverse trifluoromethylated 2,3,4,5-tetrahydro-1,2,4-triazines in 81-97% yield with a broad substrate scope, including aryl, benzyl, and alkyl hexahydro-1,3,5-triazine.

Cu(I)-Catalyzed gem-Aminoalkynylation of Diazo Compounds: Synthesis of Fluorinated Propargylic Amines

The gem-aminoalkynylation of fluorinated diazo compounds catalyzed by a simple Cu(I) salt is described. This three-component reaction allows the synthesis of propargylic amines with broad functional group tolerance. Both electron-rich and electron-poor anilines can be used as nucleophiles and alkyl-, aryl-, and silyl-substituted EthynylBenziodoXoles (EBX) as electrophiles.

Silver-Catalyzed Direct Synthesis of Trifluoromethylated Enaminopyridines and Isoquinolinones Employing Trifluorodiazoethane

This Letter reports a Ag-catalyzed three-component approach for the N-alkenylation of 2-aminopyridines employing aldehydes and trifluorodiazoethane. Unlike the known reactions of trifluorodiazoethane with imines, which generate Mannich adducts, aziridines, or triazolines depending on the substrates and conditions, this reaction, after Mannich addition, proceeds via a carbene formation and 1,2-aryl migration sequence to afford (E)-enaminopyridines. This surprising selectivity, which is effective for a wide range of aldehydes and 2-aminopyridines, has been subsequently explored to access trifluoromethylated isoquinolinones.

Synthesis of Fluoro-, Monofluoromethyl-, Difluoromethyl-, and Trifluoromethyl-Substituted Three-Membered Rings

This Minireview describes recent advances toward the synthesis of fluoro-, monofluoromethyl-, difluoromethyl-, and trifluoromethyl-substituted three-membered rings such as cyclopropanes, aziridines, epoxides, episulfides, cyclopropenes, and 2 H-azirines. The main synthetic methodologies since 2016 for cyclopropanes and since 2010 for the other three-membered rings are reported.

Asymmetric synthesis of CF2-functionalized aziridines by combined strong Brønsted acid catalysis

A diastereo- and enantioselective approach to access chiral CF2-functionalized aziridines from difluorodiazoethyl phenyl sulfone (PhSO2CF2CHN2) and in situ-formed aldimines is described. This multicomponent reaction is enabled by a combined strong Brønsted acid catalytic platform consisting of a chiral disulfonimide and 2-carboxyphenylboronic acid. The optical purity of the obtained CF2-substituted aziridines could be further improved by a practical dissolution-filtration procedure.

Ag-Catalyzed Trifluoromethylative Ring Expansion of Isatins and Isatin Ketimines with Trifluorodiazoethane

A general method for the construction of trifluoromethylated 2-quinolinones has been established herein by using a trifluoromethylative ring expansion of isatin with trifluorodiazoethane. The strategy provides a platform for the rapid synthesis of a wide range of substituted 3-hydroxy-4-trifluoromethyl-2-quinolinones. This operationally simple and robust Ag-catalyzed protocol successfully transforms isatin ketimines to 3-amino-4-trifluoromethylquinolinones in excellent yields. The utility of this novel method is further illustrated by the conversion of the products into various synthetically and medicinally relevant molecules.

Enantioselective synthesis of trifluoromethyl substituted cyclohexanones via an organocatalytic cascade Michael/aldol reaction

An enantioselective (92-99% ee) Michael/aldol cascade reaction between 4,4,4-trifluoroacetoacetates and α,β-unsaturated enones was established in the presence of cinchona alkaloid-based primary amines. Various β-CF3-cyclohexanones were constructed in high yields (81-99%) as a couple of separable diastereomers. This tandem reaction was sensitive to acidic co-catalysts, with a Michael/aldol condensation process favorably occurring to generate β-CF3-cyclohexenones (42-69% yield, 84-96% ee) in the presence of trifluoroacetic acid.

Trifluoroacetimidoyl halides: a potent synthetic origin

In the review, recent advances in the synthetic applications of trifluoroacetimidoyl halides have been summarized.

Catalytic Enantioselective Cyclopropenation of Internal Alkynes: Access to Difluoromethylated Three-Membered Carbocycles

Herein we described an efficient Rh^II -catalyzed enantioselective cyclopropenation reaction of internal alkynes with a masked difluorodiazoethane reagent (PhSO₂ CF₂ CHN₂ , Ps-DFA). This asymmetric transformation offers efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes (40 examples, up to 99 % yield, 97 % ee). The synthetic utility of obtained strained carbocycles is demonstrated by subsequent stereodefined processes, including cross-couplings, hydrogenation, Diels-Alder reaction, and Pauson-Khand reaction.

Synthesis of Highly Substituted Azepanones from 2 H-Azirines by a Stepwise Annulation/Ring-Opening Sequence

Bicyclic aziridines possessing a 1-azabicyclo[4.1.0]heptan-2-one core were prepared from 2 H-azirines by a stepwise annulation sequence involving a diastereoselective allylindanation, an N-acylation, and a ring-closing metathesis to construct the six-membered ring. After hydrogenation or functionalization of the olefin, regioselective ring opening of the resulting azabicyclic compounds with carboxylic acids (or sulfur nucleophiles) afforded highly substituted azepanones possessing an ester moiety or a trifluoromethyl group and a tetrasubstituted carbon at the α and β positions of the nitrogen atom, respectively.

Telescoped, Divergent, Chemoselective C1 and C1-C1 Homologation of Imine Surrogates: Access to Quaternary Chloro- and Halomethyl-Trifluoromethyl Aziridines

A conceptually novel, high‐yielding, mono‐ or bis‐homologation was realized with lithium halocarbenoids and enables the one‐step, fully chemocontrolled assembly of a new class of quaternary trifluoromethyl aziridines. Trifluoroacetimidoyl chlorides (TFAICs) act as convenient electrophilic platforms, enabling the addition of either one or two homologating elements by simply controlling the stoichiometry of the process. Mechanistic studies highlighted that the homologation event, carried out with two different carbenoids (LiCH₂Cl and LiCH₂F), leads to fluoromethyl analogues in which the first nucleophile is employed for constructing the cycle and the second for decorating the resulting molecular architecture.

A rhodium-catalyzed three-component reaction of arylisocyanides, trifluorodiazoethane, and activated methylene isocyanides or azomethine ylides: an efficient synthesis of trifluoroethyl-substituted imidazoles

A novel method for the synthesis of trifluoroethyl-substituted imidazoles is reported via a rhodium-catalyzed three-component reaction of isocyanides, 2,2,2-trifluorodiazoethane and activated methylene isocyanides or azomethine ylides.

Perfluoroalkyl Aziridines with Ruthenium Porphyrin Carbene Intermediates

A new and efficient synthesis of multifunctionalized perfluoroalkyl aziridines via a ruthenium-perfluoroalkylcarbene intermediate is described. With Ru( p-Cl-TPP)CO as the catalyst, in situ generated C _nF_{2 n+1}CHN₂ from C _nF_{2 n+1}CH₂NH₃Cl underwent a cascade of nitrone formation/1,3-diploar cycloaddition/rearrangement reactions with nitrosoarenes and alkynes to give a variety of multifunctionalized perfluoroalkyl aziridines in good to high yields and with moderate to high diastereoselectivity. The ruthenium-perfluoroalkylcarbene intermediates obtained through the stoichiometric reaction of ruthenium porphyrin and C _nF_{2 n+1}CHN₂ were spectroscopically characterized.

Heptafluoroisopropyl diazomethane (i-C3F7CHN2): in situ generation and synthesis of pyrazoles

A novel chemical reagent, heptafluoroisopropyl diazomethane (i-C₃F₇CHN₂), has been generated in situ in aqueous media. It reacts with electron-deficient alkynes towards polyfluorinated pyrazoles that are important in agrochemistry.

Fe-Catalyzed insertion of fluoromethylcarbenes generated from sulfonium salts into X–H bonds (X = Si, C, P)

The Fe-catalyzed insertion of fluoromethylcarbenes including trifluoromethylcarbene and difluoromethylcarbene into X–H (X = Si, C and P) bonds is described.