Successive C-C bond cleavage, fluorination, trifluoromethylthio- and pentafluorophenylthiolation under metal-free conditions to provide compounds with dual fluoro-functionalization

A Strategic Synthesis of Fluoroethers via Ring-Opening Fluorinative Beckmann Fragmentation

An SN1-type fluorination method for monofluoroethers is developed. The key to this reaction is fluorinative C-C bond cleavage that is driven by oxygen-assisted Beckmann fragmentation. To enable this transformation, cyclic α-aryloxyoximes derived from 3-coumaranone and 1-indanones were investigated as substrates, using N,N-diethylaminosulfur trifluoride (DAST) as a dual-role reagent of an oxime activator and fluoride donor. This method features the synthesis of an underdeveloped chemical motif with simple and mild operating conditions.

Ring-Opening Fluorination of Carbo/Heterocycles and Aromatics: Construction of Complex and Diverse Fluorine-Containing Molecules

Fluorine-containing molecules have attracted much attention in medicinal, agrochemical, and materials sciences because they offer unique physical and biological properties. Therefore, many efficient fluorination reactions have been developed over the years. Recent advancements in fluorination chemistry have expanded the range of substrates, and regioselectivity/stereoselectivity control has also been achieved. Ring-opening fluorination is an efficient method to construct complex fluorine-containing molecules with diversity, starting from simple cyclic compounds. This review aims to summarize developments in ring-opening fluorination, particularly with larger-sized cyclic compounds. Fluorine introduction and bond cleavage of cyclic compounds such as carbocycles, heterocycles, and aromatics provide efficient access to fluorine-containing compounds that are difficult to be synthesized by conventional methods.

Catalytic Synthesis of 5-Fluoro-2-oxazolines: Using BF3·Et2O as the Fluorine Source and Activating Reagent

Hypervalent iodine catalyst-catalyzed nucleophilic fluorination of unsaturated amides using BF₃·Et₂O as the fluorine source and activating reagent was reported. Various 5-fluoro-2-oxazoline derivatives were synthesized in good to excellent yields (up to 95% isolated yield) within 10 min. The process was efficient and metal-free under mild conditions. A mechanism involving a fluorination/1,2-aryl migration/cyclization cascade was proposed on the basis of previous work and experimental results.

Electrophilic N-trifluoromethylthiophthalimide as a fluorinated reagent in the synthesis of acyl fluorides

Herein we report the deoxygenated fluorination of readily available carboxylic acids. A series of acyl fluorides have been synthesized using shelf-stable N-trifluoromethylthiophthalimide as a fluorinated reagent for the first time.

2-Pyridinylmethyl borrowing: base-promoted C-alkylation of (pyridin-2-yl)-methyl alcohols with ketones via cleavage of unstrained C(sp3)–C(sp3) bonds

2-Pyridinylmethyl Borrowing: Transition-metal-free 2-pyridinylmethyl borrowing C-alkylation of alcohols access to ketones is developed. This unstrained C(sp3)–C(sp3) bonds cleavage of unactivated alcohols avoids the use of transition metals.

[4+2] Cycloaddition Reactions of β-Naphtha-1-thioquinones Generated from 2-Naphthols and DAST

An original and facile method for the generation of β-naphtha-1-thioquinone using DAST and 2-naphthol has been developed. A series of dehydro-2-naphthol-1-sluphides or naphtha-oxathiane derivatives were synthesized by in-situ Diels-Alder cycloaddition...

Acyl Fluorides from Carboxylic Acids, Aldehydes, or Alcohols under Oxidative Fluorination

We describe a novel reagent system to obtain acyl fluorides directly from three different functional group precursors: carboxylic acids, aldehydes, or alcohols. The transformation is achieved via a combination of trichloroisocyanuric acid and cesium fluoride, which facilitates the synthesis of various acyl fluorides in high yield (up to 99%). It can be applied to the late-stage functionalization of natural products and drug molecules that contain a carboxylic acid, an aldehyde, or an alcohol group.

Tertiary-Amine-Initiated Synthesis of Acyl Fluorides from Carboxylic Acids and CF3 SO2 OCF3

A convenient method for deoxyfluorination of aromatic and aliphatic carboxylic acids with CF₃ SO₂ OCF₃ in the presence of a suitable base at room temperature has been developed. The reaction allows a straightforward access to a variety of acyl fluorides and proves that CF₃ SO₂ OCF₃ is an effective deoxyfluorination reagent for carboxylic acids. The method features simplicity, expeditiousness, high efficiency, ease of handling, good functional group tolerance, a wide range of substrates, excellent yields of products, compatibility of many amine initiators, use of environmentally friendly reagents, and effortless removal of byproducts. This reaction represents the first utilization of trifluoromethyl trifluoromethanesulfonate as a fluorination reagent.

Synthesis of indoline-fused eight-membered azaheterocycles through Zn-catalyzed dearomatization of indoles and subsequent base-promoted C-C activation

A cascade reaction involving the Zn-catalyzed dearomatization of indoles, base-promoted ring-expansion and intramolecular S_NAr reaction has been developed. This process realized a novel, atom economical and efficient synthesis of indoline-fused eight-membered azaheterocycles in a one pot manner.

Synthesis of Acyl Fluorides via DAST-Mediated Fluorinative C-C Bond Cleavage of Activated Ketones

A new protocol for preparation of acyl fluorides was developed by recognizing activated ketones as starting materials. The method provides a different scope compared with previously reported methods that employ carboxylic acids as substrates. A working hypothesis of pull-and-push-driven fluorinative C-C bond cleavage was successfully demonstrated by the simple addition of diethylaminosulfur trifluoride (DAST) derivatives to α-oximinoketones. The designed reaction system led to a highly efficient and chemoselective reaction. The wide availability of the ketones allowed for a range of synthetically useful aryloyl and aliphatic acyl fluorides including those containing chiral skeletons. The method is mild, fast, scalable, and potentially one-pot operative.

Pd-catalyzed fluoro-carbonylation of aryl, vinyl, and heteroaryl iodides using 2-(difluoromethoxy)-5-nitropyridine

Acyl fluorides have recently gained a lot of attention as robust and versatile synthetic tools in synthetic chemistry. While several synthetic routes to acyl fluorides have been reported, a procedure involving direct insertion of the "fluoro-carbonyl" moiety using a single reagent has not yet been realized. Here we report the preparation of acyl fluorides by palladium-catalyzed fluoro-carbonylation of aryl, vinyl, and heteroaryl iodides using 2-(difluoromethoxy)-5-nitropyridine under CO-free conditions. 2-(difluoromethoxy)-5-nitropyridine is a stable, colorless solid that can be used as an alternative to the toxic gaseous formyl fluoride, which is commonly used under fluoride catalysis conditions. A wide variety of acyl fluorides are efficiently and safely obtained in high yield (up to 99%). A broad range of functional groups is tolerated under the optimized reaction conditions and the method can be applied to the late-stage fluoro-carbonylation of structurally complex C_sp2-iodides, including bioactive derivatives, such as Fenofibrate, Isoxepac, and Tocopherol. Furthermore, the one-pot transformation of aryl-iodides, including drug-like molecules, into the corresponding amides by successive fluoro-carbonylation/amidation reactions, demonstrates the potential synthetic utility of this strategy.

Synthesis of polysubstituted quinolines through promoter-regulated selective annulation and C–C bond cleavage from 2-styrylanilines and β-keto esters

I₂ and Mn(OAc)₃ regulated annulation of 2-styrylanilines and β-keto esters is accomplished for chemoselective synthesis of 2-alkylquinolines and quinoline-2-carboxylates.

Merging base-promoted C-C bond cleavage and iron-catalyzed skeletal rearrangement involving C-C/C-H bond activation: synthesis of highly functionalized carbazoles

An efficient and atom-economical methodology for the synthesis of multi-substituted carbazoles starting from α-aryl ketones and ynones under mild reaction conditions has been developed. This process goes through Cs2CO3 promoted C-C σ-bond activation of α-aryl ketones followed by highly selective C-H bond activations and C-C bond fragmentations in a one-pot operation.

Synthesis of fluoro-functionalized diaryl-λ3-iodonium salts and their cytotoxicity against human lymphoma U937 cells

Conscious of the potential bioactivity of fluorine, an investigation was conducted using various fluorine-containing diaryliodonium salts in order to study and compare their biological activity against human lymphoma U937 cells. Most of the compounds tested are well-known reagents for fluoro-functionalized arylation reactions in synthetic organic chemistry, but their biological properties are not fully understood. Herein, after initially investigating 18 fluoro-functionalized reagents, we discovered that the ortho-fluoro-functionalized diaryliodonium salt reagents showed remarkable cytotoxicity in vitro. These results led us to synthesize more compounds, previously unknown sterically demanding diaryliodonium salts having a pentafluorosulfanyl (SF₅) functional group at the ortho-position, that is, unsymmetrical ortho-SF₅ phenylaryl-λ³-iodonium salts. Newly synthesized mesityl(2-(pentafluoro-λ⁶-sulfanyl)phenyl)iodonium exhibited the greatest potency in vitro against U937 cells. Evaluation of the cytotoxicity of selected phenylaryl-λ³-iodonium salts against AGLCL (a normal human B cell line) was also examined.

The CF3-DAST-induced deacylative trifluoromethylthiolation of cyclic 1,3-diketones/lactams/lactones and its extension to deacylative pentafluorophenylthiolation

CF₃-DAST-induced deacylative trifluoromethylthiolation of cyclic 1,3-diketones lactams, and lactones that provides cyclic trifluoromethylthioketones, lactams and lactones is reported.

Synthesis of Sulfur Perfluorophenyl Compounds Using a Pentafluorobenzenesulfonyl Hypervalent Iodonium Ylide

A novel pentafluorobenzenesulfonyl hypervalent iodonium ylide 3 was designed and synthesized as a useful tool for the preparation of sulfur pentafluorophenyl compounds containing a C₆F₅S or C₆F₅SO₂ unit. Electrophilic pentafluorophenylthiolation of enamines, formal [3+2] cycloaddition reaction of nitriles and alkynes, and intramolecular S_NAr cyclization were achieved using iodonium ylide 3. The fluoro-click reaction was also demonstrated using one of the products via an intermolecular S_NAr reaction with heterocentered nucleophiles.

Asymmetric synthesis of C–F quaternary α-fluoro-β-amino-indolin-2-ones via Mannich addition reactions; facets of reactivity, structural generality and stereochemical outcome

An asymmetric detrifluoroacetylative Mannich reaction between in situ generated tertiary enolates and sulfinyl-imines has been explored. The reaction provides a new access to α-fluoro-β-amino-indolin-2-ones with tetrasubstituted fluorinated stereogenic center.

Cleavage of 1,3-dicarbonyls through oxidative amidation

The oxidative cleavage of 1,3-diketones with amines is shown in the presence of iodine and azide anions, amides are obtained.

Chemoselective C(α)–C(β) bond cleavage of saturated aryl ketones with amines leading to α-ketoamides: a copper-catalyzed aerobic oxidation process with air

An unprecedented chemoselective C(α)–C(β) bond cleavage of simple saturated aryl ketones with amines leading to α-ketoamidesvia a copper-catalyzed aerobic oxidation process with air has been disclosed.

Selective Oxidative Decarbonylative Cleavage of Unstrained C(sp(3))-C(sp(2)) Bond: Synthesis of Substituted Benzoxazinones

A transition metal (TM)-free practical synthesis of biologically relevant benzoxazinones has been established via a selective oxidative decarbonylative cleavage of an unstrained C(sp(3))-C(sp(2)) bond employing iodine, sodium bicarbonate, and (t)butyl hydroperoxide in DMSO at 95 °C. Control experiments and Density Functional Theory (DFT) calculations suggest that the reaction involves a [1,5]H shift and extrusion of CO gas as the key steps. The extrusion of CO has also been established using PMA-PdCl2.