Synthesis of Polysubstituted Trifluoromethylpyridines from Trifluoromethyl-α,β-ynones

A copper-catalyzed tandem cyclization reaction of N-acyl enamines and electron-deficient alkynes: direct synthesis of alkynyl substituted pyridines

A copper-catalyzed coupling-cyclization reaction of N-acyl enamides with electron-deficient alkynes is developed. This reaction tolerates a wide range of N-acyl enamines and provides a simple and efficient method for the synthesis of 3-alkynyl-substituted pyridines in good to high yields from easily available acyclic starting materials with only water and hydrogen as the by-products in a single step.

Novel Synthetic Method and Insecticidal Evaluation of CF3-Containing Polycyclic Neonicotinoid Derivatives

The modification of active ingredients with a trifluoromethyl group represents a significant approach for the discovery of highly active pesticides. Herein, we developed a novel [3 + 3] annulation reaction of neonicotinoid precursors and trifluoromethyl-α,β-ynones and synthesized a series of CF3-containing polycyclic neonicotinoid derivatives in high efficiency. The insecticidal activity results indicated that most of the target compounds showed good insecticidal activities against Aphis craccivora and Nilaparvata lugens at a concentration of 100 mg/L. In particular, compounds 3o and 4k had LC50 values of 1.53 and 1.47 mg/L against A. craccivora, respectively, which were comparable to that of imidacloprid (LC50 = 1.30 mg/L). The honeybee toxicity predictive model also indicated the potential low honeybee toxicity of target compounds 3o and 4k. The molecular docking study revealed that the target compounds 3o and 4k exhibited a favorable binding mode with the Lymnaea stagnalis acetylcholine-binding protein and the R55T-mutated resistant model.

Synthesis of CF3-Azafluorenes through the Cascade Reaction of 2H-Imidazoles with CF3-Ynones

A concise synthesis of trifluoromethyl (CF3)-substituted azafluorenes based on the reaction of 5-aryl-2H-imidazoles with CF3-ynones is reported. The reaction proceeds through C-H activation-initiated formal [3+2] cycloaddition to give spiro[imidazole-4,1'-indene] as a key intermediate, followed by its retro [3+2] cycloaddition, isomerization, and enamine nucleophilic addition. This synthesis of CF3-azafluorene derivatives via simultaneous formation of both the indene and the pyridine scaffolds through cascade C-H/C-C/C-N bond cleavage and C≡C bond formation has not been disclosed before. Moreover, the products thus obtained showed antiproliferative activity against cancer cell lines.

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.

NIS-Promoted Chemodivergent and Diastereoselective Synthesis of Pyrrolinyl and Cyclopentenyl Spiropyrazolones via Regulated Cyclization of Alkylidene Pyrazolones with Enamino Esters

An N-iodosuccinimide-promoted annulation of alkylidene pyrazolones with enamino esters has been explored to construct a spiropyrazolone moiety through a Michael addition/iodination/intramolecular nucleophilic substitution sequence. When the reaction was performed in acetonitrile at 100 °C, it furnished pyrrolinyl spiropyrazolones exclusively in an anti configuration through N-attacking cyclization. When the reaction was performed in dimethyl sulfoxide at 80 °C in the presence of K2HPO4, it afforded cyclopentenyl spiropyrazolones exclusively in the syn configuration through C-attacking cyclization. A plausible mechanism has also been proposed.

Divergent synthesis of pyrrolizine derivatives through C-H bond functionalization of pyrroles

Presented herein is the synthesis of diversely functionalized pyrrolizines from the reaction of N-alkoxycarbamoyl pyrroles with CF3-ynones. The formation of the product is based on a C-H bond activation-initiated cascade process including N-alkoxycarbamoyl group-directed alkenylation of the pyrrole scaffold followed by simultaneous intramolecular nucleophilic addition along with cleavage and transfer of the directing group. By taking advantage of the rich chemistry of the transferred alkoxycarbamoyl moiety, the products could be transformed into a series of structurally and biologically interesting pyrrolizine derivatives. To our knowledge, this is the first example in which the N-alkoxycarbamoyl unit acted as a transferable and transformable directing group for the divergent synthesis of pyrrolizines.

Synthesis of CF3-Substituted N-Heterocyclic Compounds Based on C-H Activation-Initiated Formal [2 + 3] Annulation Featuring with a Latent Nucleophilic Site

Presented herein is a novel synthesis of CF3-substituted pyrrolo[1,2-a]indole derivatives based on the cascade reactions of N-alkoxycarbamoyl indoles with CF3-ynones. Mechanistically, the formation of a product involves a tandem process initiated by Rh(III)-catalyzed and N-alkoxycarbamoyl group-directed regioselective C2-H alkenylation of the indole scaffold followed by in situ removal of the directing group and intramolecular N-nucleophilic addition/annulation under one set of reaction conditions. To our knowledge, this is the first example in which a N-alkoxycarbamoyl unit initially acts as a directing group for C2-H functionalization of the indole scaffold and is then removed to provide the required reactive NH-moiety for subsequent intramolecular condensation. Moreover, the products thus obtained could be conveniently transformed into structurally and biologically attractive cycloheptenone fused indole derivatives through an acid-promoted cascade transformation. In addition, studies on the activity of selected products against human cancer cell lines demonstrated their potential as lead compounds for the development of novel anticancer drugs.

Solvent-Dependent Selective Synthesis of CF3-Tethered Indazole Derivatives Based on Multiple Bond Activations

Presented herein is a solvent-dependent selective synthesis of CF₃-tethered indazole derivatives via the cascade reactions of 1-arylpyrazolidinones with trifluoromethyl ynones. Mechanistically, the formation of the title products involves cascade N-H/C-H/C-N/C-C bond cleavage along with pyrazole ring formation and pyrazolidinone ring opening. For the formation of a pyrazole scaffold, 1-phenylpyrazolidinone acts as a C2N2 synthon, while trifluoromethyl ynone serves as a C1 synthon. Meanwhile, trifluoromethyl ynone also acts as an enol unit to facilitate the ring opening of the pyrazolidinone ring and provide a trifluoropropenoxy fragment via cleavage of the alkynyl triple bond and migration of the cleaved moiety. When the reaction was run in trifluoroethanol instead of DCE, it selectively afforded indazole derivatives tethered with a trifluoroethoxy moiety through in situ transesterification. To our knowledge, this is the first synthesis of CF₃-tethered indazole derivatives via concurrent alkynyl activation, pyrazole formation, and CF₃ migration.

Recent developments in the synthesis of nitrogen-containing heterocycles from β-aminovinyl esters/ketones as CC-N donors

Nitrogen-containing heterocycles are ubiquitous fragments of numerous natural products, pharmaceuticals, designed bioactive drug candidates and agrochemicals. During the past few decades, these compounds have received considerable attention from the synthetic chemistry community, and great efforts have been focused on the development of concise and efficient methods for the synthesis of these heterocyclic skeletons. In this review, we summarize a diverse range of synthetic methods employing β-aminovinyl esters(ketones) as key CC-N-synthons to furnish useful bioactive heterocyclic frameworks, such as quinolines, pyridines, pyrazines, pyrroles, indoles, oxazoles, imidazoles, thiazoles, isothiazoles, pyrazoles, triazoles, and azepines, thus offering new opportunities and expanding the toolbox of synthetic chemistry reactions.

Recent advances in transition-metal catalyzed directed C–H functionalization with fluorinated building blocks

This review focuses on the advances in transition-metal catalyzed reactions with fluorinated building blocks via directed C–H bond activation for the construction of diverse organic molecules with an insight into the probable mechanistic pathway.

Synthesis of 2-trifluoromethylquinolines through rhodium-catalysed redox-neutral [3 + 3] annulation between anilines and CF3-ynones using traceless directing groups

Rhodium-catalysed [3 + 3]-cycloaddition of acetanilides with CF3-ynones was achieved through a traceless directing-group strategy, which delivered 2-trifluromethylquinolines exhibiting favorable blue emissions.

Regioselective Synthesis of 2,4-Diaryl-6-trifluoromethylated Pyridines through Copper-Catalyzed Cyclization of CF3-Ynones and Vinyl Azides

A novel copper-catalyzed cyclization of readily available vinyl azides with CF₃-ynones is steadily achieved under mild conditions to furnish the versatile 2,4-diaryl-6-trifluoromethylated pyridine products, which are of great interest in medicinal chemistry. The generation of the vinyl iminophosphorane intermediates from vinyl azides through the Staudinger-Meyer reaction ensures the subsequent 1,4-addition process with CF₃-ynones in this transformation.

Practical Synthesis of α-Trifluoromethylated Pyridines Based on Regioselective Cobalt-Catalyzed [2+2+2] Cycloaddition using Trifluoromethylated Diynes with Nitriles

Regioselective cobalt-catalyzed [2+2+2] cycloaddition using fluorine-containing diynes with nitriles was described. Cycloaddition of fluorinated diynes with nitriles under the influence of CoCl2(phen), zinc bromide, and zinc dust in dichloroethane at 80°C for 3 h took place smoothly, exclusively affording the corresponding α-fluoroalkylated pyridines in excellent yields. In addition, dinitriles as substrate were also found to be suitable for this reaction, giving the corresponding fluoroalkylated bipyridine derivatives in excellent yields.