Soft-Hard Acid-Base-Controlled C−H Trifluoroethoxylation and Trideuteriomethoxylation of Anilides

Photocatalytic C-H Trifluoroethoxylation of (Hetero)arenes

The trifluoroethoxy group (OCH2CF3) is a valuable motif prevalent in pharmaceuticals and agrichemicals. Herein, we present a simple radical trifluoroethoxylation method that enables nondirected functionalization of C-H bonds of a broad array of substrates, providing access to (hetero)aryl trifluoroethyl ethers. The current protocol tolerates a variety of synthetically and pharmacologically relevant functional groups. Applicability is also demonstrated through the late-stage functionalization of biorelevant molecules and marketing drugs.

Synthesis of Polyfluoroalkyl Aryl Ethers Mediated by Sulfuryl Fluoride as a Traceless Activator

Herein, we report the metal-free synthesis of polyfluoroalkyl aryl ethers via nucleophilic substitution of fluorosulfonates, obtained in one pot by bubbling of sulfuryl fluoride (SO2F2). Polyfluoroalkyl aryl ethers are present in a variety of biologically active compounds, but previous methods for accessing them required metal catalysts or harsh conditions. With this method, their synthesis is possible under mild conditions and with a short reaction time (30 min) from commercially available starting materials and in yields of ≤97%. Various fluorinated alcohols could be used as electrophiles, and a diversity of electron-withdrawing groups on the aryl or heteroaryl group were tolerated.

N-Trifluoroethoxy Benzotriazolium Triflate: A Readily Available Reagent for Direct Radical Trifluoroethoxylation of Alkenes

Herein, we describe the development and application of a novel benzotriazole-based reagent toward radical trifluoroethoxylation. Various alkene classes, including styrene derivatives, enol carbonates, and allyl silanes, are viable reaction partners in this transformation, yielding diverse trifluoroethoxylated products. Furthermore, this method is readily applicable for the late-stage modification of natural product and drugs molecules. Mechanistic and computational studies suggest the intermediacy of an OCH2CF3 radical generated under photocatalytic conditions.

Borate-mediated aryl polyfluoroalkoxylation under transition-metal-free conditions

We describe the transition-metal-free coupling for polyfluoroalkoxy arenes using polyfluoroalkoxy borates, which serve as counterions to diaryliodonium salts and transferring mediators of polyfluoroalkoxy groups. This strategy demonstrates high functional group compatibility owing to the low nucleophilicity of the borate mediator, thus offering a practical approach for synthesizing diverse polyfluoroalkoxy arenes.

Transition-metal-catalyzed C-H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XRF, X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp2) and C(sp3) centers with SCF3, SeCF3, or OCH2CF3 groups among others, by C-H bond activation. The scope and limitations of these transformations are discussed in this review.

Enroute sustainability: metal free C-H bond functionalisation

The term "C-H functionalisation" incorporates C-H activation followed by its transformation. In a single line, this can be defined as the conversion of carbon-hydrogen bonds into carbon-carbon or carbon-heteroatom bonds. The catalytic functionalisation of C-H bonds using transition metals has emerged as an atom-economical technique to engender new bonds without activated precursors which can be considered as a major drawback while attempting large-scale synthesis. Replacing the transition-metal-catalysed approach with a metal-free strategy significantly offers an alternative route that is not only inexpensive but also environmentally benign to functionalize C-H bonds. Recently metal free synthetic approaches have been flourishing to functionalize C-H bonds, motivated by the search for greener, cost-effective, and non-toxic catalysts. In this review, we will highlight the comprehensive and up-to-date discussion on recent examples of ground-breaking research on green and sustainable metal-free C-H bond functionalisation.

Rh-Catalyzed Oxidation and Trifluoroethoxylation of N-Aryl-pyrrolidin-2-ones : A Domino Approach for the Synthesis of N-Aryl-5-(2,2,2-trifluoroethoxy)-1,5- dihydro-2H-pyrrol-2-ones

The synthesis of trifluoroethoxylated dihydropyrrolidones via rhodium-catalyzed oxidation and trifluoroethoxylation of pyrrolidones is presented in this paper. This process realized trifluoroethoxylation of non-activated sp3 C-H by domino approach for the...

Broadening of horizons in the synthesis of CD3-labeled molecules

In the light of the recent potentials of deuterated molecules as pharmaceuticals or even in mechanistic understanding, efficient methods for their synthesis are continually desired. CD₃-containing molecules are prominent amongst these motifs due to the parallel of the "magic methyl effect": introducing a methyl group into pharmaceuticals could positively affect biological activities. The trideuteromethyl group is bound to molecules either by C, N, O, or S atom. For a long time, the preparation methods of such labeled compounds were underestimated and involved multi-step syntheses. More recently, specific approaches dealing with the direct incorporation of the CD₃ group have been developed. This Review gives an overview of the methods for the preparation of CD₃-labeled molecules from conventional functional group interconversion techniques to catalytic approaches and include radical strategy. Detailed reaction mechanisms are also discussed.

Competition between N and O: use of diazine N-oxides as a test case for the Marcus theory rationale for ambident reactivity

The preferred site of alkylation of diazine N-oxides by representative hard and soft alkylating agents was established conclusively using the 1H-15N HMBC NMR technique in combination with other NMR spectroscopic methods. Alkylation of pyrazine N-oxides (1 and 2) occurs preferentially on nitrogen regardless of the alkylating agent employed, while O-methylation of pyrimidine N-oxide (3) is favoured in its reaction with MeOTf. As these outcomes cannot be explained in the context of the hard/soft acid/base (HSAB) principle, we have instead turned to Marcus theory to rationalise these results. Marcus intrinsic barriers (ΔG ‡ 0) and Δr G° values were calculated at the DLPNO-CCSD(T)/def2-TZVPPD/SMD//M06-2X-D3/6-311+G(d,p)/SMD level of theory for methylation reactions of 1 and 3 by MeI and MeOTf, and used to derive Gibbs energies of activation (ΔG ‡) for the processes of N- and O-methylation, respectively. These values, as well as those derived directly from the DFT calculations, closely reproduce the observed experimental N- vs. O-alkylation selectivities for methylation reactions of 1 and 3, indicating that Marcus theory can be used in a semi-quantitative manner to understand how the activation barriers for these reactions are constructed. It was found that N-alkylation of 1 is favoured due to the dominant contribution of Δr G° to the activation barrier in this case, while O-alkylation of 3 is favoured due to the dominant contribution of the intrinsic barrier (ΔG ‡ 0) for this process. These results are of profound significance in understanding the outcomes of reactions of ambident reactants in general.

Selective Synthesis of N-Cyano Sulfilimines by Dearomatizing Stable Thionium Ions

For the selective synthesis of N-cyano sulfilimines, we have developed a new method based on the soft-soft interaction between thionium ion electrophiles and cyanonitrene nucleophiles. The stable thionium ion was successfully obtained by oxidative dearomatization using phenyliodine (III) diacetate (PIDA) in N,N-dimethylformamide (DMF). The sulfur imination reactions were tolerant to a wide range of functional groups and exhibited high selectivities and excellent yields. The existence of thionium ion intermediates was confirmed by ultraviolet/visible (UV/vis) spectroscopy and ¹H NMR experiments.

The mechanochemical synthesis of quinazolin-4(3H)-ones by controlling the reactivity of IBX

Performing any synthesis using several arylamines and hypervalent iodine(V) reagents by direct mixing is unrealistic because of the high exothermic reaction or explosion. Herein we demonstrate, when anilines were substituted with an amide group at the ortho-position, successful chemical reactions could be performed due to intramolecular control. At maximum contact of the reacting substances, i.e., under solvent-free mechanochemical conditions, 2-aminobenzamides, aryl-, alkylaldehydes and the iodine(V) reagent o-iodoxybenzoic acid (IBX) led to substituted quinazolin-4(3H)-one derivatives in fair yields.