Brønsted Acid-Catalyzed Asymmetric Friedel-Crafts Alkylation of Indoles with Benzothiazole-Bearing Trifluoromethyl Ketone Hydrates

Organocatalytic Enantioselective Friedel-Crafts Reaction of Phenanthrenequinones and Indoles

An efficient stereoselective synthesis of 10-hydroxy-10-(1H-indol-3-yl)-9-(10H)-phenanthrene derivatives was realized through an organocatalyzed Friedel-Crafts reaction of phenanthrenequinones and indoles using a (S,S)-dimethylaminocyclohexyl-squaramide as the catalyst. Under the optimized conditions, the desired chiral products were obtained in good yields (73-90%) with moderate to high ee values (up to 97% ee). Two pairs of synthesized enantiomers were subjected to evaluation of their antiproliferative activities on four types of human cancer cell lines and one human umbilical vein endothelial cell line using the CCK-8 assay. The results indicated that stereoselectivity had obvious impacts on biological activity. (S)-4g was found to have optimal cytotoxicity against the A549 cell line and a good safety profile for human normal cells, which was better than the inhibitory activity of the positive control drug (doxorubicin).

A facile access to aliphatic trifluoromethyl ketones via photocatalyzed cross-coupling of bromotrifluoroacetone and alkenes

Biological molecules incorporating trifluoromethyl ketones (TFMKs) have emerged as reversible covalent inhibitors, aiding in the management and treatment of inflammatory diseases, cancer, and respiratory conditions. TFMKs, renowned for their versatile binding properties and adaptability, are pivotal in the rational design of novel drugs for diverse diseases. The photocatalytic insertion of alkenes, abundant feedstocks, into the α-carbon of trifluoromethylacetone represents a highly effective and atom-economical method for synthesizing valuable TFMKs. However, these processes typically necessitate high-energy photoirradiation (λ > 300 nm, Hg lamp) and stoichiometric oxidants to generate the acetonyl radical from acetone. In our study, we demonstrate the visible-light photocatalytic radical addition into olefins using bromotrifluoroacetone as the trifluoroacetonyl radical precursor under mild conditions. Aliphatic trifluoromethyl ketones or the corresponding bromo-substituted products can be obtained by selecting an appropriate photocatalyst and solvent. Comprehensive experimental investigations, including cyclic voltammetry, Stern-Volmer quenching studies, and kinetic isotope effects, corroborate the synthesis of trifluoroacetonyl radical species from bromotrifluoroacetone under photoredox conditions. Further, we demonstrate the efficient synthesis of an oseltamivir derivative bearing a trifluoromethylketone moiety, which shows promising biological activity. Hence, this methodology will streamline the direct introduction of trifluoromethyl ketone into biological target molecules during drug discovery.

Catalyst-free C(sp3)-H functionalization of methyl azaarenes with heteroaromatic trifluoromethyl ketone hydrates: "all-water" synthesis of α-trifluoromethyl tertiary alcohols

An efficient catalyst-free C(sp³)-H bond functionalization of methyl azaarenes with heteroaromatic trifluoromethyl ketone hydrates in neat water has been developed for the synthesis of α-trifluoromethyl tertiary alcohols bearing N-heteroaromatics. This method not only features excellent efficiency, broad substrate scope, catalyst-free conditions, and easy gram-scale preparation but also represents a new and rare example of "all-water" synthesis of trifluoromethylated molecules.

Electron-Deficient Fluoroarene-Mediated Synthesis of Trifluoromethyl Ketones from Carboxylic Acids

Fluoroarene-mediated trifluoromethylation of carboxylic acids for the synthesis of trifluoromethyl ketones is disclosed. The fluoroarene activates the acid group and generates the fluoride source in situ for the trifluoromethylation reaction. The present protocol is safe and metal-free, operates under mild reaction conditions, and does not require any external additives to generate trifluoromethyl anion. The current transformation provides good functional group tolerance and also delivers 92% and 88% yields of trifluoromethyl ketones in batch and continuous flow, respectively.

Design, Catalyst-Free Synthesis of New Novel α-Trifluoromethylated Tertiary Alcohols Bearing Coumarins as Potential Antifungal Agents

A new method for the synthesis of α-trifluoromethylated tertiary alcohols bearing coumarins is described. The reaction of 3-(trifluoroacetyl)coumarin and pyrrole provided the target compounds with high yields under catalyst-free, mild conditions. The crystal structure of compound 3fa was investigated by X-ray diffraction analysis. The biological activities, such as in vitro antifungal activity of the α-trifluoromethylated tertiary alcohols against Fusarium graminearum, Fusarium oxysporum, Fusarium moniliforme, Rhizoctonia solani Kuhn, and Phytophthora parasitica var nicotianae, were investigated. The bioassay results indicated that compounds 3ad, 3gd, and 3hd showed broad-spectrum antifungal activity in vitro. Compound 3cd exhibited excellent fungicidal activity against Rhizoctonia solani Kuhn, with an EC₅₀ value of 10.9 μg/mL, which was comparable to that of commercial fungicidal triadimefon (EC₅₀ = 6.1 μg/mL). Furthermore, molecular docking study suggested that 3cd had high binding affinities with 1W9U, like argifin.

Recent Advances in the Catalytic Asymmetric Friedel-Crafts Reactions of Indoles

Functionalized chiral indole derivatives are privileged and versatile organic frameworks encountered in numerous pharmaceutically active agents and biologically active natural products. The catalytic asymmetric Friedel-Crafts reaction of indoles, catalyzed by chiral metal complexes or chiral organocatalysts, is one of the most powerful and atom-economical approaches to access optically active indole derivatives. Consequently, a wide range of electrophilic partners including α,β-unsaturated ketones, esters, amides, imines, β,γ-unsaturated α-keto- and α-ketiminoesters, ketimines, nitroalkenes, and many others have been successfully employed to achieve a plethora of functionalized chiral indole moieties. In particular, strategies for C-H functionalization in the phenyl of indoles require incorporation of a directing or blocking group in the phenyl or azole ring of indole. The discovery of chiral catalysts which can control enantiodiscrimination has gained a great deal of attention in recent years. This review will provide an updated account on the application of the asymmetric Friedel-Crafts reaction of indoles in the synthesis of diverse chiral indole derivatives, covering the timeframe from 2011 to today.

Theoretical Design of a Catalyst with Both High Activity and Selectivity in C-H Borylation

Improving both the activity and selectivity of the C-H borylation reaction is currently a hot research topic but also a challenge. In this regard, we suggest a multistrategy combining directing group, coordination unsaturated metal center, and cationic character. Based on Reek's catalyst, we designed a new unsaturated cationic catalyst (1) featuring a directing group for C-H borylation. The calculated free energy barrier of C-H activation is only 7.2 kcal/mol, indicating that the cationic catalyst has higher activity than the original neutral catalyst in this process. Moreover, the comparison suggests that the ortho-C-H borylation pathway is more favorable than the meta and para pathways. The catalyst deconstructions are further performed and prove that the ortho-selectivity is attributed to hydrogen-bonding interactions between the directing group and the substrate, although the ortho site is sterically and electronically unfavorable.

Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update

The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications in various fields. Among an extremely wide variety of asymmetric reactions catalyzed by chiral systems, we are interested in: asymmetric cyclopropanation, Friedel–Crafts reaction, Mannich and Michael reaction, and other stereoselective processes conducted in the presence of zinc ions. This paper describes the achievements of the above-mentioned asymmetric transformations in the last three years. The choice of reactions is related to the research that has been carried out in our laboratory for many years.

Trifluoromethylation of Benzoic Acids: An Access to Aryl Trifluoromethyl Ketones

The trifluoromethylation of benzoic acids with TMSCF₃ was achieved through nucleophilic substitution with the use of anhydrides as an in situ activating reagent. Under the reaction conditions, a wide range of carboxylic acids including the bioactive ones worked well, thus providing a facile and efficient method for preparing aryl trifluoromethyl ketones from the readily available starting materials.