β ‐Trifluoromethyl α , β ‐unsaturated Ketones: Efficient Building Blocks for Diverse Trifluoromethylated Molecules

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.

Fluoride-Catalyzed Cross-Coupling of Silylamides to CF3-Acrylates: Access to Highly Functionalized Trifluoromethylated and Quaternary Fluorinated Molecular Architectures

A direct and simple catalytic coupling of nonfluorinated and fluorinated silylbutenamides with β-CF3 α,β-unsaturated esters mediated by fluoride ion was carried out. The transformation proceeded with excellent yields to afford new, highly functionalized trifluoromethylated and quaternary fluorinated products.

Iridium(III)-catalyzed β-trifluoromethyl enone carbonyl-directed regioselective ortho-C(sp2)-H olefination

Due to the lower LUMO energy level at the β-position of α,β-unsaturated-β-trifluoromethyl enone than that of its non-fluorinated counterpart, there is a challenge to activate the sp2 C-H bond of aromatic rings. Herein, we have reported iridium(III)-catalyzed β-trifluoromethyl enone carbonyl-directed regioselective aromatic C(sp2)-H olefination with acrylates under oxidative conditions. Furthermore, coupling with natural product-derived acrylates, scale-up and product diversification have also been performed.

Iodine-promoted transfer of dihydrogen from ketones to alkenes, triphenylmethyl, and diphenylmethyl derivatives

Herein, a novel class of transfer hydrogenation agent, cycloheptanone, was successfully employed in metal-free hydrogenation facilitated by iodine. A series of alkenes, triphenylmethyl derivatives, and diphenylmethyl derivatives were reduced to the desired compounds in moderate to excellent yields. The transfer hydrodeuteration of alkenes using α-deuterated cyclododecanone exhibited high regioselectivity. Preliminary mechanism studies confirmed the origins of the two hydrogen atoms involved in the reduction of alkenes. The current study paves the way for the use of ketones as unique transfer hydrogenation agents in chemical synthesis.

Chiral-Boron-Complex Catalyzed Asymmetric Inverse-Electron-Demand Aza-Diels-Alder Reaction of β-Trifluoromethyl α,β-Unsaturated Ketones with Cyclic N-Sulfonyl Ketimines

A highly efficient asymmetric inverse-electron-demand aza-Diels-Alder reaction of β-trifluoromethyl α,β-unsaturated ketone with cyclic N-sulfonyl ketimines catalyzed by (R)-3,3'-I2-BINOL-boron-complex was developed. A broad range of fused piperidine derivatives bearing stereogenic carbon containing CF3 motifs were prepared in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr, and >99% ee). This protocol had the characteristics of mild reaction conditions, high efficiency, and high stereoselectivity.

Base-catalyzed diastereodivergent thia-Michael addition to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones

Base-catalyzed diastereodivergent thia-Michael addition of thiols to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones is reported. By tuning the base-catalyst (i-Pr2NEt, DABCO, or P2-t-Bu), a range of chiral thia-Michael adducts was synthesized in good yields with high diastereoselectivities. A plausible mechanism was proposed on the basis of the experimental results. This work is complementary to the existing methods offering advantages, e.g., switchable diastereoselectivity using a readily synthesized chiral starting material, a cheap and readily available base catalyst, and a simple and practical operation, enabling synthetic application in organic synthesis.

Fluorinated Vinyl Sulfonium Salts and Their Synthetic Utilization

The fluorinated building block strategy and the direct fluorination strategy are of great importance for the synthesis of new fluorinated molecules. These strategies complement each other and can be combined to develop a new methodology for the construction of a wide variety of fascinating organofluorine compounds. In our opinion, the versatile building blocks used in this method should satisfy the following conditions: 1) readily prepared from commercially available reagents; 2) easy to handle; 3) storage under ordinary conditions without noticeable decomposition; 4) wide applicability. Based on the aforementioned requirements, we focused on the use of vinyl sulfonium salts. This brief review describes the synthesis of five types of fluorinated vinyl sulfonium salts and their reactions. Especially, we featured typical fluorinated groups containing trifluoromethyl (CF3 ), difluoromethyl (CF2 H), monofluoromethyl (CFH2 ), monofluoro (F) or β-bromotetrafluoroethyl (BrCF2 CF2 ) moieties in combination with vinyl sulfonium salts.

Photoredox-Catalyzed Chlorotrifluoromethylation of Arylallenes: Synthesis of a Trifluoromethyl Building Block

A new class of trifluoromethyl building blocks─2-trifluoromethyl allyl chlorides─have been obtained through a photoredox-catalyzed chlorotrifluoromethylation of aryl allenes. The reaction proceeded in a regio- and stereoselective manner. A trifluoromethylated analog of the flunarizine drug was synthesized.

Rhodium(III)-Catalyzed Conjugate Addition of β-CF3-Enones with Quinoline N-Oxides

The site-selective incorporation of a trifluoromethyl group into biologically active molecules and pharmaceuticals has emerged as a central topic in medicinal chemistry and drug discovery. Herein, we demonstrate the rhodium(III)-catalyzed conjugate addition of β-trifluoromethylated enones with quinoline N-oxides, which result in the generation of β-trifluoromethyl-β'-quinolinated ketones. The reaction proceeds under mild conditions with complete functional group tolerance. The synthetic applicability was showcased by successful gram-scale experiments and valuable synthetic transformations of coupling products.

Catalytic and Chemodivergent Synthesis of 1-Substituted 9H-Pyrrolo[1,2-a]indoles via Annulation of β-CF3 Enones with 3-Substituted Indoles

Chemodivergent reactions are more advantageous in organic synthesis that yield diversely functionalized scaffolds from common starting materials. Herein, we report an efficient metal-free chemodivergent protocol for the synthesis of 1-substituted 9H-pyrrolo[1,2-a]indole derivatives in the presence of catalytic amounts of Lewis acid/Brønsted acid conditions using 3-substituted indoles and β-trifluoromethyl-α,β-unsaturated ketones. Fine-tuning of the catalyst and solvent system in the reaction conditions deliver the trifluoromethyl, trifluoroethylcarboxylate, or carboxylic acid substituents on the C1-position of 9H-pyrrolo[1,2-a]indole derivatives in situ. It is postulated that the solvent and LA/BA catalyst interaction was found to be crucial for the catalytic C-F activation in these transformations.

Stereoselective synthesis of tri-substituted tetrahydrothiophenes and their in silico binding against mycobacterial protein tyrosine phosphatase B

A facile approach to tri-substituted tetrahydrothiophenes via thia-Michael/aldol has been developed. The cascade reaction was carried out in the presence of 5 mol% of DABCO in ethyl acetate to afford diversely functionalized tetrahydrothiophenes (THTs) with excellent diastereoselectivity. The present methodology has broad substrate tolerance. Gram-scale reaction proceeds with equal efficiency. Functional group transformations further highlight the synthetic potential of the THTs. An asymmetric version of the cascade reaction has also been investigated and a maximum of 72% ee was observed with cinchonidine derived squaramide. Moreover, in silico based molecular docking followed by deep learning based affinity prediction and molecular dynamics simulation analysis indicate the synthesized THT derivatives can act as potent competitive inhibitors of MptpB at low micromolar to nanomolar concentrations. In silico ADME analysis further suggests the plausibility of these compounds to act as future anti-mycobacterial therapeutic leads.

Transition-metal-free synthesis of trifluoromethylated benzoxazines via a visible-light-promoted tandem difunctionalization of o-vinylanilides with trifluoromethylsulfinate

A Umemoto's reagent-free and cost-effective method for synthesis of trifluoromethylated benzoxazines by 9,10-phenanthrenedione visible-light photocatalysis is described in this article.

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.

α-Trifluoromethyl Carbanion-catalyzed Intermolecular Stetter Reaction of Aromatic Aldehydes with 2-Bromo-3,3,3-trifluoropropene: Synthesis of β-Alkoxyl-β-trifluoromethylated Ketones

The intermolecular Stetter reaction of aromatic aldehydes with 2-bromo-3,3,3-trifluoropropene is achieved by the in situ generated α-trifluoromethyl carbanion catalyst. It not only represents the first example for α-trifluoromethyl carbanion-catalyzed umpolung reaction but also reveals a new protocol for the umpolung of aldehydes. Various useful β-alkoxyl-β-trifluoromethylated ketones were obtained in high yields, which could further convert to attractive bioactive compounds. Mechanism studies indicated an intramolecular 1,4-shift of the hydrogen atom was involved in this reaction.

Carbonylative coupling of simple alkanes and alkenes enabled by organic photoredox catalysis

A visible-light-driven direct carbonylative coupling of simple alkanes and alkenes via the combination of a hydrogen atom transfer process and photoredox catalysis has been demonstrated. Employing the N-alkoxyazinium salt as the oxidant and the precursor of an oxygen radical, a variety of α,β-unsaturated ketones could be obtained in a metal-free fashion.

Rh(III)-Catalyzed Annulation of 2-Biphenylboronic Acid with Diverse Activated Alkenes

Rhodium(III)-catalyzed annulation of 2-biphenylboronic acids with three classes of activated alkenes has been realized, leading to the synthesis of fused or bridged cyclic skeletons via transmetalation-initiated C-H activation. In the annulative coupling of 2-biphenylboronic acid with a CF₃-substituted enone, the bulky cyclopentadienyl ligand (Cp^tBu) in the catalyst proved effective to promote the reductive elimination process prior to protonolysis, affording the [4 + 2] annulated products instead of the simple 1,4-addition product. Seven-membered rings were obtained when disubstituted cyclopropenones were employed. Bridged cycles were isolated from the coupling of 2-biphenylboronic acid with benzoquinones as a result of 2-fold Michael additions. The substrate scopes were found to be broad with up to 99% yield under air-tolerant conditions.