An Efficient Difluorohydroxylation of Indoles Using Selectfluor as a Fluorinating Reagent

Silver-Enabled Dearomative Trifluoromethoxylation of Indoles

The only known method for the dearomative trifluoromethoxylation of indoles is preliminary, with only one substrate successfully undergoing the reaction. In this study, we not only developed a broadly applicable method for indole dearomative trifluoromethoxylation but also achieved divergent trifluoromethoxylation by fine-tuning the reaction conditions. Under optimized conditions, with a silver salt and an easily handled OCF3 reagent, various indoles smoothly underwent dearomatization to afford a diverse array of ditrifluoromethoxylated indolines in 50-84% isolated yields with up to 37:1 diastereoselectivity, and fluorinated trifluoromethoxylated indolines were obtained with exclusive trans selectivity. In addition, the reaction conditions were compatible with other heteroaromatic rings as well as styrene moieties.

Catalyst-Free gem-Difluorination/Spirocyclization of Indole-2-carboxamides: Synthesis of C2-Spiroindoline Derivatives

A catalyst-free gem-difluorination/spirocyclization reaction has been successfully developed for the synthesis of gem-difluorinated C2-spiroindoline derivatives from indole-2-carboxamides. The resulting gem-difluorinated C2-spiroindolines can be easily converted into 2-spiropseudoindoxyls through hydrolysis. This method offers the benefits of simple operation, convenient access to raw materials, and mild conditions. Dual function of Selectfluor in this reaction is noteworthy as it can serve as both a fluorinating agent and an alkaline accelerator precursor.

Phosphine Catalysis of the Fluorination of Unactivated Tertiary Alkyl Chlorides under Mild and Convenient Conditions

Due to the significance of organofluorine compounds in disciplines ranging from medicine to agriculture to materials science, the invention of new methods for the creation of carbon-fluorine bonds is an important objective. Among the underdeveloped dimensions in this area are the fluorination of hindered alkyl halides (particularly chlorides) and the discovery of catalysts for such fluorination processes. Herein, we report a mild method for the fluorination of unactivated tertiary alkyl chlorides (and bromides), catalyzed by inexpensive PPh3. This straightforward process is compatible with a range of hindered electrophiles and a variety of functional groups.

Polyhalogenation-Facilitated Spirolactonization at the meta-Position of Phenols

A novel dearomative spirolactonization/polyhalogenation of phenols that employs hypervalent iodine PhICl₂ (iodobenzene dichloride) as both an oxidant and chlorine source with an indispensable base, or only using NBS (N-bromosuccinimide) without any additives, is presented. Halide participations are a vital factor in the cascade reaction of 3'-hydroxy-[1,1'-biphenyl]-2-carboxylic acids with good selectivities and reactivities and induced the rapid constructions of multiple C-halogen bonds and directional C═O bonds in a one-step operation under mild conditions. In gaining a good understanding of the mechanism, the increase in number of bromine atoms was inferred rationally from the spirolactonization process, assisted by DFT calculations and high-resolution mass spectrometry. Mechanistic experiments suggest that the formation of a stable carbocation intermediate plays a great role in the migration of oxygen to spirolactonization.

Bismuth-Mediated α-Arylation of Acidic Diketones with ortho-Substituted Boronic Acids

The α-arylation of cyclic and fluoroalkyl 1,3-diketones is made challenging by the highly stabilized nature of the corresponding enolates, and is especially difficult for sterically demanding aryl partners. As a general solution to this problem, we report the Bi-mediated oxidative coupling of acidic diones and ortho-substituted arylboronic acids. Starting from a bench-stable bismacycle precursor, a sequence of B-to-Bi transmetallation, oxidation and C-C bond formation furnishes the arylated diones. Development of methodology that tolerates both sensitive functionality and steric demand is supported by interrogation of key reactive intermediates. Application of our strategy to cyclic diones enables the concise synthesis of important agrochemical intermediates which were previously prepared using toxic Pb reagents. This methodology also enables the first ever arylation of fluoroalkyl diones which, upon condensation with hydrazine, provides direct access to valuable fluoroalkyl pyrazoles.

A Straightforward Approach to Fluorinated Pyrimido[1,2-b]indazole Derivatives via Metal/Additive-Free Annulation with Enaminones, 3-Aminoindazoles, and Selectfluor

A novel and efficient three-component reaction with two C-N bonds and one C-F bond formation has been reported, which provides a straightforward route to a variety of fluorinated pyrimido[1,2-b]indazole derivatives. This transformation has the advantage of excellent functional group compatibility, including aliphatic and aromatic substituents enaminones. Moreover, metal and additives are not necessary for this reaction, which is of great significance for the synthesis and application of fluorinated heterocycles.

Selective electrophilic di- and mono-fluorinations for the synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones by Selectfluor-triggered multi-component reaction

A simple and efficient domino protocol for the selective synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones was established from readily available 2-aminoacetophenones and iso(thio)cyanates mediated by Selectfluor. The reaction outcomes are...

Fluorination of 2H-Indazoles Using N-Fluorobenzenesulfonimide

An efficient, simple, and metal-free fluorination of 2H-indazoles has been developed using N-fluorobenzenesulfonimide (NFSI) in water under ambient air. This transformation provides direct access to fluorinated indazole derivatives with broad functionalities in satisfactory yields. The experimental results suggest a radical mechanistic pathway of this protocol.

Synthesis and biological evaluation of fluoro-substituted spiro-isoxazolines as potential anti-viral and anti-cancer agents

Electrophilic fluorine-mediated dearomative spirocyclization has been developed to synthesize a range of fluoro-substituted spiro-isoxazoline ethers and lactones. The in vitro biological assays of synthesized compounds were probed for anti-viral activity against human cytomegalovirus (HCMV) and cytotoxicity against glioblastomas (GBM6) and triple negative breast cancer (MDA MB 231). Interestingly, compounds 4d and 4n showed significant activity against HCMV (IC50 ∼ 10 μM), while 4l and 5f revealed the highest cytotoxicity with IC50 = 36 to 80 μM. The synthetic efficacy and biological relevance offer an opportunity to further drug-discovery development of fluoro-spiro-isoxazolines as novel anti-viral and anti-cancer agents.

Synthesis of 3-selanylbenzo[b]furans promoted by SelectFluor®

A simple and practical protocol for the synthesis of 3-selanyl-benzo[b]furans mediated by the SelectFluor® reagent was developed. This novel methodology provided a greener alternative to generate 3-substituted-benzo[b]furans via a metal-free procedure under mild conditions. The intramolecular cyclization reaction was carried out employing an electrophilic selenium species generated in situ through the reaction between SelectFluor® and organic diselenides. The formation of this electrophilic selenium species (RSe-F) was confirmed by heteronuclear NMR spectroscopy, and its reactivity was explored.

Shielding Effect of Micelle for Highly Effective and Selective Monofluorination of Indoles in Water

Highly selective direct monofluorination of indoles and arenes was developed through an approach that allows site-specific solubility of substrate and fluorine source in the micelle. This approach was highly selective for a broad range of substrates with excellent functional group tolerance. Differences in binding constant and solubility of indoles and arenes in the micelle allowed the fine-tuning of selectivity. Control experiments suggested a radical pathway and provided insight into the role of micelles of the environmentally benign amphiphile PS-750-M. Dynamic light scattering experiments strongly indicated the site-specific solubility of the substrate and fluorine source. The methodology was successfully adapted to gram scale, and the E-factor established from a recycle study indicated that the process is environmentally responsible and sustainable.

Fluorination-triggered tandem cyclization of styrene-type carboxylic acids to access 3-aryl isocoumarin derivatives under microwave irradiation

A practical and straightforward synthetic route through a fluorination-triggered tandem cyclization of styrene-type carboxylic acids was developed to construct a variety of 4-fluoro-3-aryl-3,4-dihydroisocoumarins and 3-arylisocoumarins under microwave irradiation. This novel protocol features mild reaction conditions and operational simplicity, with good yields.

Lewis acid promoted fluorine-alkoxy group exchange reactions for the synthesis of 5-alkoxy-4,4-difluoroisoxazoline systems

Lewis acid promoted substitution of fluorine yields novel 5-alkoxylated 4,4-difluoroisoxazolines via S_N1 type processes.

Asymmetric Arylation of 2,2,2-Trifluoroacetophenones Catalyzed by Chiral Electrostatically-Enhanced Phosphoric Acids

A series of highly reactive metal-free chiral phosphoric acids possessing positively charged phosphonium ion substituents are reported and have been applied to Friedel-Crafts alkylations of indoles and 2,2,2-trifluoromethyl aryl ketones. These catalysts are orders-of-magnitude more active and have similar or better enantioselectivities than their noncharged analogues. High tolerance to a range of substrates with electron-withdrawing and electron-donating substituents was also observed.

A Zn(OTf)2 catalyzed Ugi-type reaction of 3-(2-isocyanoethyl)indoles with indole-derived ketimines: rapid access to hexacyclic spiroindolines

A Zn(OTf)₂ catalyzed Ugi-type reaction of 3-(2-isocyanoethyl)indoles and indole-derived ketimines was developed for the synthesis of hexacyclic spiroindolines featuring three stereocenters including two quaternary stereocenters.

Catalyst-free Synthesis of 6-Hydroxy Indoles via the Condensation of Carboxymethyl Cyclohexadienones and Amines

An efficient catalyst-free synthesis of 6-hydroxy indoles from carboxymethyl cyclohexadienones and primary amines has been developed. The aza-Michael addition of the in situ formed enamine, generated through the condensation of carboxymethyl unit of the substrates with an external amine, to cyclohexadienone moiety followed by rearomatization reaction to provide such indoles. Anilines, aliphatic amines, α-chiral aliphatic amines, or even ammonia were used as amine counterpart. Some of the cyclohexadienones gave 6-amino indoles instead of 6-hydroxy indoles using the Re₂O₇ catalyst. Various post methodological transformations were performed to explore the synthetic utility of the synthesized hydroxy indoles.

Ag-Catalyzed difluorohydration of β-alkynyl ketones for diastereoselective synthesis of 1,5-dicarbonyl compounds

A new catalytic difluorohydration of β-alkynyl ketones using NFSI as the fluorinating reagent has been established, diastereoselectively providing difluoride 1,5-dicarbonyl products, and some of them were converted into difluorinated isoquinolines.

Fluorination methods in drug discovery

Fluorination reactions of medicinal and biologically-active compounds will be discussed. Late stage fluorination strategies of medicinal targets have recently attracted considerable attention on account of the influence that a fluorine atom can impart to targets of medicinal importance, such as modulation of lipophilicity, electronegativity, basicity and bioavailability, the latter as a consequence of membrane permeability. Therefore, the recourse to late-stage fluorine substitution on compounds with already known and relevant biological activity can provide the pharmaceutical industry with new leads with improved medicinal properties. The fluorination strategies will take into account different fluorinating reagents, either of nucleophilic or electrophilic, and of radical nature. Diverse families of organic compounds such as (hetero)aromatic rings, and aliphatic substrates (sp(3), sp(2), and sp carbon atoms) will be studied in late-stage fluorination reaction strategies.

Iron-catalyzed domino indole fluorination/allenic aza-Claisen rearrangement

The synthesis of 2-allenyl-2-substituted-3,3-difluoroindolines has been accomplished, taking advantage of the reaction between N-allenyl-indoles and Selectfluor under iron catalysis.

Metal-free intermolecular C–O cross-coupling reactions: synthesis of N-hydroxyimide esters

Selectfluor-mediated intermolecular C–O cross coupling reaction for the synthesis of N-hydroxyimide esters was achieved under metal-free conditions.

Fluorination of 2-substituted benzo[b]furans with Selectfluor™

An efficient protocol was developed to access 3-fluoro-2-hydroxy-2-substituted benzo[b]furans with Selectfluor™ as the fluorinating reagent in MeCN and water. By utilizing SOCl₂/Py as the dehydrating agent, the compounds above were readily converted to 3-fluorinated, 2-substituted benzo[b]furans in high yields.

A trifluorinated thiazoline scaffold leading to pro-apoptotic agents targeting prohibitins

A new class of small molecules, with an unprecedented trifluorothiazoline scaffold, were synthesized and their pro-apoptotic activity was evaluated. With an EC50 in the low micromolar range, these compounds proved to be potent inducers of apoptosis in a broad spectrum of tumor cell lines, regardless of the functional status of p53. Fast structure-activity relationship studies allowed the preparation of the strongest apoptosis-inducing candidate. Using a high performance affinity purification approach, we identified prohibitins 1 and 2, key proteins involved in the maintenance of cell viability, as the targets for these compounds.

An intramolecular cascade cyclization of 2-aryl indoles: efficient methods for the construction of 2,3-functionalized indolines and 3-indolinones

Efficient intramolecular N/O-nucleophilic cyclization of 2-aryl indoles has been developed to afford the corresponding 2-aza-3-oxaindolines and 3-indolinones in 80-95% yield. The methods provided convenient access to fused imidazo[1,2-c]oxazolidinone, oxazolidine, or tetrahydro-1,3-oxazine cores under mild conditions.

Aminofluorination of 2-alkynylanilines: a Au-catalyzed entry to fluorinated indoles

The scope and limitations of gold-catalyzed tandem cycloisomerization/fluorination reactions of unprotected 2-alkynylanilines to have access to 3,3-difluoro-2-aryl-3H-indoles and 3-fluoro-2-arylindoles are described. An unprecedented aminoauration/oxidation/fluorination cascade reaction of 2-alkynylanilines bearing a linear alkyl group on the terminal triple bond is reported.