Direct Synthesis of Tri-/Difluoromethyl Ketones from Carboxylic Acids by Cross-Coupling with Acyloxyphosphonium Ions

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.

Synthesis of 18F-labelled aryl trifluoromethyl ketones with improved molar activity

A method for the radiosynthesis of 18F-labelled aryl trifluoromethyl ketones starting from widely available Weinreb amides using [18F]fluoroform is presented. The method uses potassium hexamethyldisilazane as base and delivers products in high molar activity (up to 24 GBq μmol-1) and excellent radiochemical conversions. The applicability for PET tracer synthesis is demonstrated by the radiosynthesis of ten (hetero)aryl trifluoromethylketones, bearing electron-withdrawing and -donating substituents including a derivative of bioactive probenecid.

Chemoselective Synthesis of α-Halo-α,α-difluoromethyl Ketones from Trimethyl(phenylethynyl)silane

Here, we describe a novel strategy for chemoselective synthesis of α-halo-α,α-difluoromethyl ketones (-COCF3 and -COClCF2 motifs) from trimethyl(phenylethynyl)silane under catalyst-free and mild conditions. Commercially available Selectfluor or additional NaCl as halogen reagent was employed to complete this transformation, thereby demonstrating the potential synthetic value of this new reaction in organic synthesis.

Divergent Generation of the Difluoroalkyl Radical and Difluorocarbene via Selective Cleavage of C-S Bonds of the Sulfox-CF2SO2Ph Reagent

A new difluoroalkylation reagent Sulfox-CF2SO2Ph bearing both sulfoximine and sulfone moieties was prepared from commercially available SulfoxFluor and PhSO2CF2H. On one hand, the Sulfox-CF2SO2Ph reagent could act as a (phenylsulfonyl)difluoromethyl radical source under photoredox catalysis, in which the arylsulfoximidoyl group is selectively removed. On the other hand, under basic conditions, Sulfox-CF2SO2Ph could serve as a difluorocarbene precursor for S- and O-difluoromethylations with S- and O-nucleophiles, respectively, in which the phenylsulfonyl group in Sulfox-CF2SO2Ph is selectively removed (followed by α-elimination of the arylsulfoximidoyl group).

Access to Trifluoromethylketones from Alkyl Bromides and Trifluoroacetic Anhydride by Photocatalysis

Aliphatic trifluoromethyl ketones are a type of unique fluorine-containing subunit which play a significant role in altering the physical and biological properties of molecules. Catalytic methods to provide direct access to aliphatic trifluoromethyl ketones are highly desirable yet remain underdeveloped, partially owing to the high reactivity and instability of trifluoroacetyl radical. Herein, we report a photocatalytic synthesis of trifluoromethyl ketones from alkyl bromides with trifluoroacetic anhydride. The reaction features dual visible-light and halogen-atom-transfer catalysis, followed by an enabling radical-radical cross-coupling of an alkyl radical with a stabilized trifluoromethyl radical. The reaction provides straightforward access to aliphatic trifluoromethyl ketones from readily available and cost-effective alkyl halides and trifluoroacetic anhydride (TFAA).

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.

Copper-Catalyzed Synthesis of Difluoromethyl Alkynes from Terminal and Silyl Acetylenes

An efficient method for the direct C(sp)-H difluoromethylation of terminal alkynes and the desilylation-difluoromethylation of (trimethylsilyl)acetylenes is disclosed. The copper-catalyzed transformation provides access to a wide range of structurally diverse CF₂H alkynes in good yields, utilizing a (difluoromethyl)zinc reagent and an organic oxidant. The difluoromethylation of important synthons and API's is showcased. The synthetic utility of these (difluoromethyl)alkynes is demonstrated by selected cycloaddition reactions. Additionally, a slight modification to the reaction conditions allowed the selective preparation of a 2-difluoromethylindole.