Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation,Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BF_n(CN)_4−n] (n=0–2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)₂{OC(O)Et}]⁻ to result in [BF(CN)₂{OC(O)Et}]⁻ is described.     

Fluorination rates of polyolefins as a function of structure and gas atmosphere

Polyolefins and fluoropolymers were reacted with elemental fluorine under carefully controlled conditions in a thermobalance adapted to be compatible with fluorine gas. The fluorination reactions were monitored by measuring the mass increase as a result of hydrogen substitution by fluorine. The mass increase was directly proportional to the square root of the fluorination time, which indicates that fluorine gas diffusion to the unreacted surface is the rate determining step. The fluorination rate was increased by increasing the fluorine concentration and the fluorination temperature. The fluorination rate is higher when nitrogen rather than helium is used as diluting gas. The fluorination rate for the reaction in which CO₂ is used as diluting gas is the same as during fluorination with nitrogen as diluting gas, while the presence of oxygen dramatically decreased the fluorination rate. Oxygen is incorporated during fluorination with oxygen as diluting gas, while no functionalization was observed when CO₂ was employed as diluting gas. The effect of polymer structure on fluorination was studied. Poly(vinylfluoride) gained mass during fluorination, while no reaction was observed for poly(vinylidenefluoride). The reaction rate for polypropylene was higher than that of polyethylene. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Stereospecific Electrophilic Fluorination of Alkylcarbastannatrane Reagents

We report the use of isolable primary and secondary alkylcarbastannatrane nucleophiles in site‐specific fluorination reactions. These reactions occur without the need for transition metal catalysis or in situ activation of the nucleophile. In the absence of the carbastannatrane backbone, alkyltin nucleophiles exhibit no activity towards fluorination. When enantioenriched alkylcarbastannatranes are employed, fluorination occurs predominately via a stereoinvertive mechanism to generate highly enantioenriched alkyl fluoride compounds. These conditions can also be extended to stereospecific chlorination, bromination, and iodination reactions.     

Electrophilic Fluorination of Imidazoheterocycles by Selectfluor

Russian Journal of General Chemistry - Response surface analysis (RSA) has been used for optimization of the synthesis using selectfluor as a fluorine source and...     

Research of Fluorination Process of Rutile Concentrate

The brief review of industrial technologies of titanium-containing concentrates processing has been carried out. Drawbacks of the existing titanium manufacture schemes are shown and the necessity of the essentially new fluoride technologies development has been proved. The reactions proceeding during the fluorination of rutile concentrate with element fluoride are described in the given work. The thermodynamic research of the process has been carried using ASTRA software. Dependence of mass concentration change of titanium tetrafluoride has been investigated in products of reaction on the temperature of the process, and the choice of optimum excess of fluoride has been proved.     

对映选择性亲电氟化反应研究进展

含氟有机化合物, 特别是手性氟化物在医药、农药及功能性材料等相关领域的作用备受注目. 尽管在分子中有立体选择性地引入一个氟原子一直是有机化学家面临的一个挑战性问题, 近年来在化学家们的不断努力下, 对映选择性氟化反应研究取得重要进展. 高光学活性的手性氟化物可通过手性亲电氟化试剂诱导的立体选择性氟化反应, 基于底物的手性氟化反应以及手性催化剂诱导的不对称催化氟化反应等来制备. 特别是, 手性金属配合物和有机催化剂诱导的不对称催化氟化反应被广泛应用于各类手性氟化物的合成, 已成为不对称氟化反应研究的热点. 全面介绍对映选择性亲电氟化反应研究概况和最新进展, 讨论各种不对称氟化反应的特点及应用范围.     

电化学氟化最新进展

本文从全氟化和部分氟化角度系统地叙述了电化学氟化在国内外的最新进展情况,并简要介绍了含氟有机物在医药上的应用.     

Electrophilic Fluorination of a Highly Functionalized Pyrrole

Bromine-lithium exchange of 3-bromo-1 -(trilsopropylsilyl) pyrrole 6 followed by treatment with N-fluorobenzenesulfonimide gave the fluoropyrrole 8. Application of this methodology to the highly functionalized pyrrole 1 afforded the fluoropyrrole 4, which was found to be inaccessible by other approaches.     

Fluorination of elastomer materials

The present study aims at the surface functionalization of cross-linked natural rubber films by direct fluorination routes involving the treatment of elastomer surfaces with gaseous fluorine and its mixtures. Two different fluorination methods were evaluated to attach fluorine moieties on polyisoprene surfaces. On the one hand the fluorination was carried out with mixtures of fluorine with inert gas yielding highly non-polar surfaces. On the other hand polar surface properties were obtained in the presence of fluorine and oxygen in the reaction gas mixture (oxy-fluorination). The functionalized surfaces were characterized by means of FTIR-ATR spectroscopy and contact angle measurements. Optical microscopy was used to assess the surface morphology of the modified elastomer films and the depth of fluorination was investigated with SEM-EDX. In addition, the influence of the surface fluorination on the mechanical properties, aging stability and stability against high energy radiation (e.g. gamma-rays) of the functionalized rubber materials were determined by tensile tests.     

微波辅助离子液体合成法在亲核氟化中的应用

采用微波辅助合成法快捷、高效地制备了系列咪唑类和吡啶类离子液体,并对其在亲核氟化中的应用进行了研究.结果表明,N-苄基吡啶四氟硼酸盐([bepy]BF4)是一种稳定性高、使用效果好的离子液体.在微波作用下,以N-苄基吡啶四氟硼酸盐和乙腈为共溶剂,以氟化铯为氟化试剂,高效合成了系列含氟化合物.在优化反应条件下,其收率为54.1%～76.3%,反应时间较常规油浴加热最好时可缩短50%以上.     

Decarboxylative Fluorination of 2-Pyridylacetates

Syntheses of substituted pyridines and fluorinated compounds, which are often pharmaceutical targets, are important objectives in organic chemistry. Herein, we found that decarboxylative fluorination of lithium 2-pyridylacetates occur under catalyst-free conditions. The phenomenon can be applied to one-pot transformation of substituted methyl 2-pyridylacetate to 2-(fluoroalkyl)pyridine by decarboxylative fluorination of the intermediate lithium 2-pyridylacetate. This method was also applied to the syntheses of 2-(difluoroalkyl)pyridines.     

Inter- and Intra-Molecular Organocatalysis of SN2 Fluorination by Crown Ether: Kinetics and Quantum Chemical Analysis

We present the intra- and inter-molecular organocatalysis of S_N2 fluorination using CsF by crown ether to estimate the efficacy of the promoter and to elucidate the reaction mechanism. The yields of intramolecular S_N2 fluorination of the veratrole substrates are measured to be very small (<1% in 12 h) in the absence of crown ether promoters, whereas the S_N2 fluorination of the substrate possessing a crown ether unit proceeds to near completion (~99%) in 12 h. We also studied the efficacy of intermolecular rate acceleration by an independent promoter 18-crown-6 for comparison. We find that the fluorinating yield of a veratrole substrate (leaving group = −OMs) in the presence of 18-crown-6 follows the almost identical kinetic course as that of intramolecular S_N2 fluorination, indicating the mechanistic similarity of intra- and inter-molecular organocatalysis of the crown ether for S_N2 fluorination. The calculated relative Gibbs free energies of activation for these reactions, in which the crown ether units act as Lewis base promoters for S_N2 fluorination, are in excellent agreement with the experimentally measured yields of fluorination. The role of the metal salt CsF is briefly discussed in terms of whether it reacts as a contact ion pair or as a “free” nucleophile F⁻.     

Electrophilic fluorination: the aminopyridine dilemma

An unusually high yielding fluorination of aminopyralid (3) using F-TEDA (SELECTFLUOR™) in warm water, followed by kinetic resolution (via iterative esterification/saponification) of the crude fluorination product with dry HCl in methanol produced pure ring-fluorinated pyridine 2 in an overall yield of 31% for the two steps.     

电化学部分氟化芳基研究进展

含氟芳香化合物具有生物活性好、稳定性高、易被生物体代谢等优点,在医药和农药领域有着广泛的用途.目前芳基部分氟化的方法主要分为依赖于氟化试剂的亲电氟化方法以及反应条件苛刻甚至需要过渡金属催化的亲核氟化方法,这些方法操作繁琐并且污染环境.电化学氟化将"电能"作为一种"强氧化剂"来实现氟化反应,是一种直接、绿色且温和的氟化手...     

Facile Synthesis of Monofluoro γ-Lactones and Pyrrolidine Derivatives via Electrophilic Fluorination of Allenoic Acids and Amides

A convenient method to synthesize a series of monofluoro γ-lactones and pyrrolidine derivatives in moderate to good yields via the electrophilic fluorination of γ-allenoic acids and tosylamides using Selectfluor was developed.     

Ionic Liquids as Organocatalysts for Nucleophilic Fluorination: Concepts and Perspectives

Besides their extremely useful properties as solvent, ionic liquids (ILs) are now considered to be highly instructive tools for enhancing the rates of chemical reactions. The ionic nature of the IL anion and cation seems to be the origin of this fascinating function of ILs as organocatalyst/promoter through their strong Coulombic forces on other ionic species in the reaction and also through the formation of hydrogen bonds with various functional groups in substrates. It is now possible to tailor-make ILs for specific purposes as solvent/promoters in a variety of situations by carefully monitoring these interactions. Despite the enormous potentiality, it seems that the application of ILs as organocatalysts/promoters for chemical reactions have not been fully achieved so far. Herein, we review recent developments of ILs for promoting the nucleophilic reactions, focusing on fluorination. Various aspects of the processes, such as organocatalytic capability, reaction mechanisms and salt effects, are discussed.     

Oxidative Fluorination of Cyclopropylamides through Organic Photoredox Catalysis

We report an oxidative ring‐opening strategy to transform cyclopropylamides and cyclobutylamides into fluorinated imines. The imines can be isolated in their more stable hemiaminal form, with the fluorine atom installed selectively at the γ or δ position. Both inexpensive benzophenone with UVA light or organic and inorganic dyes with blue light could be used as photoredox catalysts to promote this process. Various fluorinated amines were then obtained by nucleophilic attack on the hemiaminals in one pot, giving access to a broad range of useful building blocks for medicinal chemistry.     

Elemental fluorine. Part 24.[1]: Fluorination of ethers by fluorine and Selectfluor

Reactions of dialkyl ethers with either fluorine or Selectfluor™ led to the formation of unusual difluorinated polyether products in modest yields. A mechanism involving initial fluorination of the site adjacent to ether oxygen followed by elimination of hydrogen fluoride, reaction of the generated enol system with a further equivalent of fluorinating agent giving an oxonium system which reacts with water during aqueous work-up to lead eventually to the products observed, is suggested.