Enantioselective α-Trifluoromethylthiolation of Carbonyl Compounds with AgSCF3 and Trichloroisocyanuric Acid

We successfully developed an enantioselective trifluoromethylthiolation of structurally diverse carbonyl compounds. Trichloroisocyanuric acid and AgSCF3 were employed to generate active electrophilic trifluoromethylthio species in situ for asymmetric C-SCF3 bond formation. A broad variety of chiral SCF3-carbon nucleophiles (pyrazolones, β-keto esters, and β-keto amides) were obtained in excellent yields with high enantioselectivities (up to 92% ee) by Cinchona alkaloid derived squaramide catalysts. The reaction exhibits high efficiency, good enantioselectivity, and high functional group tolerance, which provided a novel and efficient way for asymmetric synthesis of trifluoromethylthiolated carbonyl compounds.

Efficient synthesis of SCF3-containing 3-alkenylquinoxalinones via three-component radical cascade reaction

An efficient and practical method for the synthesis of 3-alkenylquinoxalinones containing the SCF3 group has been readily developed through a three-component radical cascade reaction involving quinoxalinones, alkynes and AgSCF3. The reaction was found to be compatible with a variety of substrates and exhibited a high functional group tolerance and complete E-selectivity. The preliminary study suggests the involvement of a SCF3 radical in the transformation.

The perfluoroalkylthiolation/decarbonylation reaction of 1,3-diketones with perfluoroalkanesulfenic acids

The perfluoroalkylthiolation/decarbonylation reactions of 1,3-dicarbonyl compounds with in situ formed perfluoroalkanesulfenic acids were achieved. Using trifluoromethanesulfonic acid as an additive, a series of α-perfluoroalkylthiolated arylethanones were obtained in moderate to good yields. A possible mechanism was proposed based on the reaction results and control experiments.

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Trifluoromethylthiolation of Hindered α-Bromoamides with Nucleophilic Trifluoromethylthiolating Reagents

General methods have not been previously developed for the synthesis of sterically hindered α-SCF₃-substituted carbonyl compounds using nucleophilic trifluoromethylthiolating reagents. Thus, we herein report sp³C-SCF₃ bond formation in hindered α-bromoamides containing 3-bromo-oxindoles and linear α-bromoamides using CuSCF₃ or AgSCF₃ under mild conditions to access sterically hindered α-SCF₃-substituted amides. This transformation is applicable to not only 3-SCF₃-substituted oxindoles but also primary and secondary amides and reveals a broad functional group tolerance. This method will benefit the fields of medicinal and agricultural chemistry.

Catalyst-Free Decarbonylative Trifluoromethylthiolation Enabled by Electron Donor-Acceptor Complex Photoactivation

A catalyst- and additive-free decarbonylative trifluoromethylthiolation of aldehyde feedstocks has been developed. This operationally simple, scalable, and open-to-air transformation is driven by the selective photoexcitation of electron donor-acceptor (EDA) complexes, stemming from the association of 1,4-dihydropyridines (donor) with N-(trifluoromethylthio)phthalimide (acceptor), to trigger intermolecular single-electron transfer events under ambient- and visible light-promoted conditions. Extension to other electron acceptors enables the synthesis of thiocyanates and thioesters, as well as the difunctionalization of [1.1.1] propellane. The mechanistic intricacies of this photochemical paradigm are elucidated through a combination of experimental efforts and high-level quantum mechanical calculations [dispersion-corrected (U)DFT, DLPNO-CCSD(T), and TD-DFT]. This comprehensive study highlights the necessity for EDA complexation for efficient alkyl radical generation. Computation of subsequent ground state pathways reveals that SH2 addition of the alkyl radical to the intermediate radical EDA complex is extremely exergonic and results in a charge transfer event from the dihydropyridine donor to the N-(trifluoromethylthio)phthalimide acceptor of the EDA complex. Experimental and computational results further suggest that product formation also occurs via SH2 reaction of alkyl radicals with 1,2-bis(trifluoromethyl)disulfane, generated in-situ through combination of thiyl radicals.

Diversity-oriented synthesis of glycomimetics

Glycomimetics are structural mimics of naturally occurring carbohydrates and represent important therapeutic leads in several disease treatments. However, the structural and stereochemical complexity inherent to glycomimetics often challenges medicinal chemistry efforts and is incompatible with diversity-oriented synthesis approaches. Here, we describe a one-pot proline-catalyzed aldehyde α-functionalization/aldol reaction that produces an array of stereochemically well-defined glycomimetic building blocks containing fluoro, chloro, bromo, trifluoromethylthio and azodicarboxylate functional groups. Using density functional theory calculations, we demonstrate both steric and electrostatic interactions play key diastereodiscriminating roles in the dynamic kinetic resolution. The utility of this simple process for generating large and diverse libraries of glycomimetics is demonstrated in the rapid production of iminosugars, nucleoside analogues, carbasugars and carbohydrates from common intermediates.

Stereoselective Synthesis of Chiral α-SCF3-β-Ketoesters Featuring a Quaternary Stereocenter

The development of new and efficient methods, reagents, and catalysts for the introduction of fluorine atoms or fluorinated moieties in molecular scaffolds has become a topic of paramount importance in organic synthesis. In this framework, the incorporation of the SCF3 group into organic molecule has often led to beneficial effects on the drug’s metabolic stability and bioavailability. Here we report our studies aimed to the stereoselective synthesis of chiral α-SCF3-β−ketoesters featuring a tetrasubstituted stereocenter. The use of a chiral auxiliary was crucial to synthesize enantiopure enamines that were reacted with N-trifluoromethylthio saccharin or phthalimide, to afford enantioenriched α-SCF3-tetrasubstitued β-keto esters. By using a readily available, inexpensive chiral diamine, such as trans-1,2-diaminocyclohexane, the fluorinated products could be obtained in modest to good yields, and, after the removal of the chiral auxiliary, α-substituted- α trifluoromethylthio-β−ketoesters were isolated with high enantioselectivity (up to 91% ee).

Formal α-trifluoromethylthiolation of carboxylic acid derivatives via N-acyl pyrazoles

A direct and general one-pot approach to α-trifluoromethylthiolated amides, esters and carboxylic acids has been successfully developed under mild, catalytic and metal-free conditions.

Novel Bifunctionalization of Activated Methylene: Base-Promoted Trifluoromethylthiolation of β-Diketones with Trifluoromethanesulfinyl Chloride

A novel bifunctionalization of activated methylene was achieved successfully through the base-promoted trifluoromethylthiolation of β-diketones or β-ketoesters with trifluoromethanesulfinyl chloride. A series of α-trifluoromethylthiolated α-chloro-β-diketones and α-chloro-β-ketoesters were obtained in moderate to good yields under mild conditions. When β-diketones containing a phenyl group with a hydroxyl or amino substituent at the ortho position were used as substrates, intramolecular trifluoromethylthiolation/cyclization reaction took place to give the corresponding cyclic products. Furthermore, the protocol could be extended to perfluoroalkylthiolation with the sodium perfluoroalkanesulfinate/POCl₃ system. On the basis of experimental results, plausible mechanisms are proposed.

Asymmetric Electrophilic Difluoromethylthiolation of Indanone-Based β-Keto Esters Using Difluoromethanesulfonyl Hypervalent Iodonium Ylides

The first electrophilic diastereoselective direct introduction of the difluoromethylthio group is described. We used a chiral auxiliary-based approach to illustrate the versatility of our recently developed difluoromethanesulfonyl hypervalent iodonium ylide reagents for the difluoromethylthiolation of indanone-based β-keto esters. Chiral SCF₂H-featuring compounds were obtained in up to 93% ee value.