Silver-Mediated [3 + 2] Cycloaddition of Azomethine Ylides with Trifluoroacetimidoyl Chlorides for the Synthesis of 5-(Trifluoromethyl)imidazoles

Recent advances in the synthesis of trifluoromethyl-containing heterocyclic compounds via trifluoromethyl building blocks

Trifluoromethylated heterocyclic compounds have played an increasingly significant role in pharmaceuticals, agrochemicals, and materials. This is because the introduction of trifluoromethyl could enhance the lipophilicity, metabolic stability, and pharmacokinetic properties of heterocyclic drug molecules. Therefore, the synthesis of trifluoromethylated heterocyclics has become a major subject of research. The construction of trifluoromethylated heterocyclics via the annulation of trifluoromethyl building blocks with suitable partners has been proved to be a powerful strategy. In this review, we systematically summarize and discuss recent advances in the preparation of trifluoromethyl-containing heterocyclics via trifluoromethyl building block strategies over the period from 2019 to the present.

DMF as an amine source: iron-catalyzed cyclization of 2H-azirines to imidazoles

A novel method has been developed for the synthesis of 1-methyl-4,5-diaryl-1H-imidazoles through Fe(II)-catalyzed cyclization of 2H-azirines and N,N-dimethylformamide (DMF) as an amine source. This transformation involves the cleavage of C-N and CN double bonds and the construction of new C-N and CN double bonds. The reaction has readily available starting materials, a wide range of substrates and mild reaction conditions. In addition, the reaction also facilitated the convenient synthesis of 1-methyl-2,4,5-triaryl-1H-imidazoles.

Diverse Synthesis of Fused Polyheterocyclic Compounds via [3 + 2] Cycloaddition of In Situ-Generated Heteroaromatic N-Ylides and Electron-Deficient Olefins

[3 + 2] Cycloaddition reactions of heteroaromatic N-ylides with electron-deficient olefins have been developed. The heteroaromatic N-ylides, in situ generated from N-phenacylbenzothiazolium bromides, can smoothly react with maleimides under very mild conditions, affording fused polycyclic octahydropyrrolo[3,4-c]pyrroles in good-to-excellent isolated yields. This reaction concept could also be extended to 3-trifluoroethylidene oxindoles and benzylidenemalononitriles as electron-deficient olefins for accessing highly functionalized polyheterocyclic compounds. A gram-scale experiment was also carried out to verify the practicability of the methodology.

Formal [4+1] Annulation of Azoalkenes with CF3-Imidoyl Sulfoxonium Ylides and Dual Double Bond Isomerization Cascade: Synthesis of Trifluoromethyl-Containing Pyrazole Derivatives

A straightforward strategy for the metal-free construction of trifluoromethyl-containing pyrazole derivatives has been achieved from readily available α-halo hydrazones and CF₃-imidoyl sulfoxonium ylides. The cascade transformation proceeds through the formal [4+1] cycloaddition followed by an unexpected dual double bond isomerization. The protocol features mild conditions, easy operation, excellent substrate compatibility, and good regioselectivity. The synthetic utility is demonstrated by scale-up reaction and further elaboration of the obtained pyrazole products.

Cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives

A new cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives has been developed. A variety of free (NH)-tetrahydro-β-carbolinones were produced in good yields. The oxidant, silver salt, can be recycled and reused.

Controllable access to trifluoromethyl-containing indoles and indolines: Palladium-catalyzed regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides

The synthesis of diverse products from the same starting materials is always attractive in organic chemistry. Here, a palladium-catalyzed substrate-controlled regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides has been developed, which provides a direct but controllable access to a variety of structurally diverse trifluoromethyl-containing indoles and indolines. In more detail, with respect to γ,δ-alkenes, 1,1-geminal difunctionalization of unactivated alkenes with trifluoroacetimidoyl chloride enables the [4 + 1] annulation to produce indoles; as for β,γ-alkenes, a [3 + 2] heteroannulation with the hydrolysis product of trifluoroacetimidoyl chloride through 1,2-vicinal difunctionalization of alkenes occurs to deliver indoline products. The structure of alkene substrates differentiates the regioselectivity of the reaction.

A palladium-catalyzed dual functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides toward the synthesis of structurally diverse trifluoromethyl-containing indoles and indolines has been developed.

The cascade coupling/iodoaminocyclization reaction of trifluoroacetimidoyl chlorides and allylamines: metal-free access to 2-trifluoromethyl-imidazolines

A metal-free cascade coupling/iodoaminocyclization reaction for the rapid assembly of 2-trifluoromethyl-imidazolines has been disclosed. The transformation applies readily accessible trifluoroacetimidoyl chlorides, allylamines and N-iodosuccinimides as the starting substrates, achieving an efficient and straightforward pathway to construct diverse imidazoline derivatives. Excellent efficiency of the reaction is observed (higher than 90% isolated yield for half of the examples), and the obtained imidazoline products bearing a pendent iodomethyl group could be easily transformed into other synthetically valuable compounds.

Copper-mediated [3 + 2] cycloaddition of trifluoroacetimidoyl chlorides and N-isocyanoiminotriphenylphosphorane for the synthesis of 3-trifluoromethyl-1,2,4-triazoles

Herein, a facile and straightforward route to synthesize 3-trifluoromethyl-1,2,4-triazoles via copper-mediated [3 + 2] cycloaddition of trifluoroacetimidoyl chlorides and N-isocyanoiminotriphenylphosphorane (NIITP) has been described.

Metal-free oxidative cyclization of trifluoroacetimidohydrazides with methylhetarenes: a facile access to 3-hetaryl-5-trifluoromethyl-1,2,4-triazoles

A metal-free oxidative cyclization of trifluoroacetimidohydrazides with methylhetarenes for the efficient synthesis of 3-hetaryl-5-trifluoromethyl-1,2,4-triazoles has been developed.

Synthesis of 5-trifluoromethyl-1,2,3-triazoles via base-mediated cascade annulation of diazo compounds with trifluoroacetimidoyl chlorides

A metal-, azide- and CF₃-reagent free approach for the synthesis of 5-trifluoromethyl-1,2,3-triazoles via base-mediated cascade annulation of diazo compounds with trifluoroacetimidoyl chlorides has been developed.