Boron-Mediated Regioselective Aromatic C-H Functionalization via an Aryl BF2 Complex

An efficient regioselective functionalization of 2-aryl-heteroarenes and aryl aldehydes via an azaaryl BF₂ complex has been developed. Mechanistically the reaction comprises fluoride to bromide ligand exchange on an aryl boron species and consecutive C-B bond cleavage to deliver a broad range of functionalized products. The reaction is high yielding, has a broad substrate scope where several different heteroarenes can be functionalized with chloro, bromo, iodo, hydroxyl, amine and BF₂ in a highly regioselective fashion. The method can be applied for late-stage functionalization or for rapid skeleton remodeling with for instance cross-couplings.

Conversion of a AuI Fluorido Complex into an N-Fluoroamido Derivative: N-F versus Au-N Reactivity

The Au^I complex [Au{N(F)SO₂ Ph}(SPhos)] (SPhos=dicyclohexyl(2',6'-dimethoxy[1,1'-biphenyl]-2-yl)phosphane) (2) bearing a fluoroamido ligand has been synthesized by reaction of the fluorido complex [Au(F)(SPhos)] (1) with NFSI (NFSI=N-fluorobenzenesulfonimide). A reaction with CO resulted in an unprecedented insertion into the N-F bond at 2. With the carbene precursor N₂ CH(CO₂ Et) N-F bond cleavage gave the Au-F bond insertion product [Au{CHF(CO₂ C₂ H₅ )}(SPhos)] (7). The presence of CNtBu led to Au-N cleavage at 2 and concomitant amide formation to give the cationic complex [Au(CNtBu)(SPhos)][N(F)SO₂ Ph)] (5), which reacted further to give FtBu as well as the cyanido complex [Au(CN)(SPhos)] (6). These results led to the development of a process for the amination of electrophilic organic substrates by transfer of the fluoroamido group NF(SO₂ Ph)^- .

anti-Markovnikov Iodofluorination of Alkenes

The fluorination of alkenes with electrophilic N-F type reagents usually occurs through a Markovnikov-type addition, and the anti-Markovnikov-type addition may require the use of a transition metal catalyst or an expensive catalyst. Herein we describe a convenient anti-Markovnikov iodofluorination of alkenes with Selectfluor/ nBu4NI. A wide substrate scope and good functional group tolerance were observed. The process allows for the construction of various C-F bonds, especially tertiary C-F bonds. The remarkable features make this protocol attractive, including convenient operations, simple reaction conditions, and the installation of an iodine atom which provides possibilities for further transformations.

Stereoselective Synthesis of Highly Substituted 1,3-Dienes via "à la carte" Multifunctionalization of Borylated Dendralenes

Despite the high relevance of 1,3-dienes, stereoselective methods to access tetrasubstituted conjugated dienes are still scarce. We here report an efficient and modular approach that provides access to multifunctional tetrasubstituted 1,3-dienes with excellent levels of regio- and stereoselectivity. This methodology is based on a tetracomponent reaction between a borylated dendralene, an organolithium reagent and two different electrophiles. Mechanistic studies reveal that this transformation proceeds through a regio- and stereoselective carbolithiation/electrophilic trapping of an in situ formed dendralenic boron-ate complex, followed by a stereoretentive halodeborylation. The ease in which complex structural dienes can be accessed and their synthetic versatility highlight the importance and utility of this method.

Recent Advances in the Application of Selectfluor as a "Fluorine-free" Functional Reagent in Organic Synthesis

Selectfluor, [1-chloromethyl-4-fluoro-1,4-diazoniabicyclo-[2.2.2]octane bis(tetrafluoroborate)], is not only an important electrophilic fluorinating agent but also a facile and efficient "fluorine-free" functional reagent in other organic reactions. In this Minireview, we will present a brief history of Selectfluor as a transition metal oxidant, fluorine cation and radical initiator in "fluorine-free" functionalizations over the last five years.

Gold-Catalyzed Cross-Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

Transition-metal-catalyzed cross-coupling reactions are central to many organic synthesis methodologies. Traditionally, Pd, Ni, Cu, and Fe catalysts are used to promote these reactions. Recently, many studies have showed that both homogeneous and heterogeneous Au catalysts can be used for activating selective cross-coupling reactions. Here, an overview of the past studies, current trends, and future directions in the field of gold-catalyzed coupling reactions is presented. Design strategies to accomplish selective homocoupling and cross-coupling reactions under both homogeneous and heterogeneous conditions, computational and experimental mechanistic studies, and their applications in diverse fields are critically reviewed. Specific topics covered are: oxidant-assisted and oxidant-free reactions; strain-assisted reactions; dual Au and photoredox catalysis; bimetallic synergistic reactions; mechanisms of reductive elimination processes; enzyme-mimicking Au chemistry; cluster and surface reactions; and plasmonic catalysis. In the relevant sections, theoretical and computational studies of Au^I /Au^III chemistry are discussed and the predictions from the calculations are compared with the experimental observations to derive useful design strategies.

Light-Mediated Formal Radical Deoxyfluorination of Tertiary Alcohols through Selective Single-Electron Oxidation with TEDA2+

The synthesis of tertiary alkyl fluorides through a formal radical deoxyfluorination process is described herein. This light-mediated, catalyst-free methodology is fast and broadly applicable allowing for the preparation of C-F bonds from (hetero)benzylic, propargylic, and non-activated tertiary alcohol derivatives. Preliminary mechanistic studies support that the key step of the reaction is the single-electron oxidation of cesium oxalates-which are readily available from the corresponding tertiary alcohols-with in situ generated TEDA2+. (TEDA: N-(chloromethyl)triethylenediamine), a radical cation derived from Selectfluor®.

The Electrophilic Fluorination of Enol Esters Using SelectFluor: A Polar Two-Electron Process

The reaction of enol esters with SelectFluor is facile and leads to the corresponding α-fluoroketones under mild conditions and, as a result, this route is commonly employed for the synthesis of medicinally important compounds such as fluorinated steroids. However, despite the use of this methodology in synthesis, the mechanism of this reaction and the influence of structure on reactivity are unclear. A rigorous mechanistic study of the fluorination of these substrates is presented, informed primarily by detailed and robust kinetic experiments. The results of this study implicate a polar two-electron process via an oxygen-stabilised carbenium species, rather than a single-electron process involving radical intermediates. The structure-reactivity relationships revealed here will assist synthetic chemists in deploying this type of methodology in the syntheses of α-fluoroketones.

Recent Trifluoromethylation Reactions. A Mini Review Paper

This review highlights recent improvement in trifluoromethylene functionalization processes with CF3 reagents, includes: Togni’s, Umemoto’s, CF3SO2Cl, CF3I, Yagupol’skii-Umemoto, TMSCF3, Langlois (CF3SO2Na) and clarifies the several designing to result the corresponding trifluoromethylated products. In this article, the selective trifluoromethylation reactions with Togni’s reagents and their analogs are detailed, which work transition metals or photoactivated Ru or Ir catalysts as single electron giver to yield CF3 radical intermediate species. This issue is to introduce a draft of diverse reports, presenting the modern reaction collect and mechanics produced during the past five years. This task is demanded by the key protocol connected with the trifluoromethylation reactions, designing to sustain researchers a straight forward understanding of such reactions and to award information for further implements.

Amidyl Radicals by Oxidation of α-Amido-oxy Acids: Transition-Metal-Free Amidofluorination of Unactivated Alkenes

A three-component transition-metal-free amidofluorination of unactivated alkenes and styrenes is presented. α-Amido-oxy acids are introduced as efficient and easily accessible amidyl radical precursors that are oxidized by a photoexcited organic sensitizer (Mes-Acr-Me) to the corresponding carboxyl radical. Sequential CO₂ and aldehyde/ketone fragmentation leads to an N-centered radical that adds to an alkene. Commercial Selectfluor is used to trap the adduct radical through fluorine-atom transfer. The transformation features by high functional-group tolerance, broad substrate scope, and practical mild conditions. Mechanistic studies support the radical nature of the cascade.

Hydrogen Bonding: Regulator for Nucleophilic Fluorination

The recent advances in nucleophilic fluorination, regulated through hydrogen bonding interactions are summarized. Two main categories of fluorine nucleophiles are discussed. Alkali-metal fluorides are widely used in various fluorination transformations because they are inexpensive and safe nucleophilic fluorine sources. But the non-controllable nucleophilicity and strong basicity of some of them cause undesired side reactions, which led to the introduction of hydrogen bonding to fine tune their nucleophilicity and basicity. In contrast, an HF-based fluorine nucleophile, HF/DMPU, is in some aspects superior to the conventional HF/pyridine (Olah's reagent) or HF/Et3 N because of the higher hydrogen bond basicity of DMPU. It has been used in several nucleophilic fluorinations such as fluorination of alkynes, fluoro-Prins reaction and fluorination of aziridines.

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.

Visible-Light-Induced Trifluoromethylation of Isonitrile-Substituted Methylenecyclopropanes: Facile Access to 6-(Trifluoromethyl)-7,8-Dihydrobenzo[k]phenanthridine Derivatives

A new visible-light-induced trifluoromethylation of isonitrile-substituted methylenecyclopropanes is developed. A range of substituted 6-(trifluoromethyl)-7,8-dihydrobenzo[k]phenanthridine derivatives are readily furnished by this newly developed tandem reaction with moderate to good yields. This reaction allows the direct formation of two six-membered rings and three new C-C bonds, including the C-CF3 bond, under visible light irradiation.