Novel and facile synthesis of fluorinated enamino ketones and amino alcohols

Selected imines and one bis-imine react via their enamine tautomers with terminal perfluorinated epoxides, e.g. hexafluoropropene oxide to produce fluorinated enamino ketones or imino ketones. In contrast, internal perfluorinated linear epoxides and one cyclic epoxide yield intermediate imino alcohols, which in one case added hexafluoroacetone, furnishing a new imino diol investigated by X-ray diffraction.     

The reaction of hexafluoropropene oxide with grignard reagents

The reactions of hexafluoropropene oxide and equimolar amounts of Grignard reagents lead to the formation of 2-halotetrafluoropropanoyl fluorides which were converted to the methyl or ethyl ester for isolation purposes. Treatment of hexafluoropropene oxide with excess Grignard reagent formed an unsaturated ketone of the type R₂CCFCOR (RCH₃ or CH₂CH₃; a route by which this product is formed is postulated.     

Heterocyclic polyfluoro-compounds. Part 34 [1]. Two-way photochemical addition of hexafluoroacetone to 1,2-dichlorofluoroethylene,and the preparation of an oxete

The well-known Paterno-Büchi reaction, which involves oxetan formation by the photochemical addition of a carbonyl compound to a carbon-carbon double bond [2], was extended to the fluorocarbon field by Harris and Coffman [3], who described the photochemical addition of fluoroaldehydes, fluoroketones, and fluoroacyl fluorides to terminal perfluoroolefins and chlorotrifluoroethylene, e.g., Subsequently, Bissel and Fields reported that low yields of oxetans were obtained from acetaldehyde and the olefins, CF₂CF₂, CF₂CFCl, and CF₂CCl₂ [4]. The reaction of hexafluoroacetone with hexafluoropropene involves the triplet state of the ketone [5].     

The use of hexafluoropropene oxide in substitutive fluorination of SbV and BiV oxygen-containing compounds

Reactions of hexafluoropropene oxide with Sb^V and Bi^V oxygen-containing compounds were studied. The E=O (E−O) groups were found to be transformed into the EF₂ (E−F) (E=Sb or Bi) groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1652–1653, August, 1998.     

Insertion reactions of difluorocarbene generated by pyrolysis of hexafluoropropene oxide to OH bond

ROCHF₂-type fluorinated ethers were synthesized by the reaction of hexafluoropropene oxide (HFPO) with alcohol or phenol. In this reaction, although the insertion reaction of difluorocarbene to OH bond and the nucleophilic attack of alcohol or phenol to HFPO were competition, the insertion reaction proceeded predominantly to give fluorinated ether in the case of low nucleophilic alcohol or phenol. In addition, high reaction pressure is advantageous to the selectivity of the fluorinated ethers in the reaction of HFPO with (CF₃)₂CHOH or C₆F₅OH.     

Merging Visible-Light Catalysis for the Direct Late-Stage Group-16–Trifluoromethyl Bond Formation

The use of visible light activation/photoredox chemistry for the generation of radical-centered chalcogen–CF₃ has gained widespread interest in the last past three years. Its subsequent reactivity for the synthesis of new chalcogen–CF₃-containing building blocks gained much attention. To date several methodologies have been developed addressing several challenges in modern organofluorine chemistry and enabled substantial progress in substrates scope and reaction conditions. This review describes these advancements with a particular focus on the reaction mechanisms.     

The reaction of hexafluoropropene oxide with alkyl lithium reagents

A series of alkyl lithium reagents has been found to react with hexafluoropropene oxide in the presence of ether to give carbinols of the type CF₃CFRCR₂OH. Butyllithium in hexane reacts “abnormally” to give the carbinol CF₃C(OH) BuCF₂Bu. Mechanisms to account for these difference are presented.     

Fluoroalkylated silylaminophosphanes and bicyclic diphosphanes: Reactivity and structures

Abstract

Phosphorus compounds containig electron withdrawing groups were prepared by degradation reactions of cyclic sulfur-nitrogen chlorides with perfluoroalkylated silylaminophosphanes and by the base catalysed attack of hexafluoroacetone on P(CN)₃ and P(NCS)₃. New results in the coordination chemistry of bicyclic diphosphanes towards transition metal carbonyls are reported and the improved oxidation of a diphosphane by the SO₂/Zn²⁺ system is discussed.     

Synthesis of Triazenes with Nitrous Oxide

Triazenes are valuable compounds in organic chemistry and numerous applications have been reported. Furthermore, triazenes have been investigated extensively as potential antitumor drugs. Here, we describe a new method for the synthesis of triazenes. The procedure involves a reagent which is rarely used in synthetic organic chemistry: nitrous oxide (N₂O, “laughing gas”). Nitrous oxide mediates the coupling of lithium amides and organomagnesium compounds while serving as a nitrogen donor. Despite the very inert character of nitrous oxide, the reactions can be performed in solution under mild conditions. A key advantage of the new procedure is the ability to access triazenes with alkynyl and alkenyl substituents. These compounds are difficult to prepare by conventional methods because the required starting materials are unstable. Some of the new alkynyltriazenes were found to display high cytotoxicity in in vitro tests on ovarian and breast cancer cell lines.     

Development of technology of perfluoroethyl isopropyl ketone production

Synthesis of perfluoroethyl isopropyl ketone by an interaction of hexafluoropropene with perfluoropropionic acid fluoride or hexafluoropropene oxide was examined. Interchangeability of perfluoropropionic acid fluoride and hexafluoropropene oxide was demonstrated. The features of perfluoroethyl isopropyl ketone synthesis were studied in polar aprotic solvents on catalysts: alkali metal fluoride. A method for obtaining perfluoroethyl isopropyl ketone by direct catalytic reaction in a tubular reactor without use of solvents was suggested and investigated. The mechanism of interaction was considered. The main impurities resulting in obtaining perfluoroethyl isopropyl ketone were determined. The methods of cleaning perfluoroethyl isopropyl ketone were worked out.     

Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone

Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K).     

Palladium-Catalyzed Arylfluorination of Alkenes: A Powerful New Approach to Organofluorine Compounds

Fluorine incorporation into organic molecules is often beneficial to their absorption, distribution, metabolism, and excretion (ADME) properties or bioactivity. As a consequence, organofluorine compounds have become quite common amongst drugs and agrochemicals, and their preparation is a highly important topic in both synthetic organic chemistry and pharmaceutical chemistry. One of the newly developed methods for accessing organofluorine compounds is Pd-catalyzed arylfluorination of alkenes. It is an olefin difunctionalization process that simultaneously introduces an aryl group and a fluorine atom into an alkene framework. This review provides a concise overview of this powerful and versatile method.     

Ruthenium-Catalyzed Site-Selective Trifluoromethylations and (Per)Fluoroalkylations of Anilines and Indoles

Introducing (per)fluoroalkyl groups into arenes continues to be an interesting, but challenging area in organofluorine chemistry. We herein report an ortho-selective C−H perfluoroalkylation including trifluoromethylations of anilines and indoles without the need of protecting groups using R_fI and R_fBr as commercially available reagents. The availability and price of the starting materials and the inherent selectivity make this novel methodology attractive for the synthesis of diverse (per)fluoroalkylated building blocks, for example, for bioactive compounds and materials.     

Reagents for Selective Fluoromethylation: A Challenge in Organofluorine Chemistry

The introduction of a monofluoromethyl moiety has undoubtedly become a very important area of research in recent years. Owing to the beneficial properties of organofluorine compounds, such as their metabolic stability, the incorporation of the CH₂F group as a bioisosteric substitute for various functional groups is an attractive strategy for the discovery of new pharmaceuticals. Furthermore, the monofluoromethyl unit is also widely used in agrochemistry, in pharmaceutical chemistry, and in fine chemicals. The problems associated with climate change and the growing need for environmentally friendly industrial processes mean that alternatives to the frequently used CFC and HFBC fluoromethylating agents (CH₂FCl and CH₂FBr) are urgently needed and also required by the Montreal Protocol. This has recently prompted many researchers to develop alternative fluoromethylation agents. This Minireview summarizes both the classical and new generation of fluoromethylating agents. Reagents that act via electrophilic, nucleophilic, and radical pathways are discussed, in addition to their precursors.     

Hexafluoropropylene Oxide–Alcohol: A Convenient System for Silica Dissolution

Abstract

A new method of silica dissolution is described. It involves the formation of a stable SiF₄ · n ROH complex (1, 1a) just from SiO₂ and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF₄ complexes can be easily converted to different organosilicon compounds of the type SiF₄L₂ and (LH)₂SiF₆ [L = 1,10-phenantroline (2a), 2,2′-dipyridyl (2b), Me₂SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategy—silicagel, sand, alumosilicates, and even rice husk.

GRAPHICAL ABSTRACT     

蒋锡夔研究员及其在物理有机化学和有机氟化学领域的成就

蒋锡夔研究员是我国物理有机化学和有机氟化学的主要奠基人。本文首先介绍蒋锡夔研究员的科学经历,然后介绍他在不同时期取得的代表性科学成就,主要包括有关四氟乙烯的亲电加成反应,氟橡胶研究,亲卤反应,自由基化学及有机分子的簇集与自卷等方面的研究。     

Reactions involving fluoride ion Part XIII. Reactions of perfluoro-4-vinylpyridine

1-Chloro-1-(2′,3′,5′,6′-tetrafluoropyridyl)tetrafluoroethane, obtained by reaction of chlorotrifluoroethylene with pentafluoropyridine in the presence of caesium fluoride, was dehalogenated over iron at 310°, giving perfluoro-4-vinylpyridine (IV). Reactions of (IV) have been surveyed; nucleophilic attack occurs at both the ring and the difluoromethylene group using MeO^- but with PhO^-, selective attack at the difluoromethylene group occurred. A dimer is produced by reaction of (IV) with CsF and the intermediate carbanion was trapped with tetrafluoropyridazine. Thermal cyclodimerisation of (IV) gave a single isomer whose structure was established by n.m.r. and by defluorination to a cyclobutene. Cyclobutanes were formed in thermal cycloaddition reactions with chlorotrifluoroethylene and with hexafluoropropene. Photochemical reaction of (IV) with hexafluoroacetone gave an oxetane.     

The Role of Oxygen Dissociation in Plasma Enhanced Chemical Vapor Deposition of Zinc Oxide from Oxygen and Diethyl Zinc

The influence of electron impact dissociation of oxygen on neutral chemistry was studied for plasma-enhanced chemical vapor deposition (PECVD) of zinc oxide using oxygen and diethyl zinc. Electron conditions in the reactor were estimated based on simulations of well-known Ar-O₂ plasmas, while the majority of the thermal chemistry was abstracted from the combustion literature. A rudimentary model of film growth was developed using the rate of oxygen dissociation as the lone adjustable parameter.n Model results were compared directly with experimental measurements of deposition rates and neutral species densities for a wide range of conditions. Good quantitative agreement between experiments and model were observed as a function of composition and rf power. The system is highly sensitive to the electron impact dissociation of oxygen, which creates the radical pool that drives the majority of the chemistry. The approach detailed here provides a framework for the development of models of oxide PECVD derived from other metalorganic precursors.     

Metal‐Free,Initiator‐Free Graphene Oxide‐Catalyzed Trifluoromethylation of Arenes

The direct C−H trifluoromethylation of arenes catalyzed by graphene oxide (GO) under safe conditions is described. This strategy is metal‐free, initiator‐free, safe, and scalable. It employs a readily available CF₃ source and the reaction can be easily controlled to obtain a mono‐trifluorinated product. This method opens a new avenue for GO‐catalyzed chemistry.     

Shedding Light Onto the Nature of Iron Decorated Graphene and Graphite Oxide Nanohybrids for CO2 Conversion at Atmospheric Pressure

We report on the design and testing of new graphite and graphene oxide-based extended π-conjugated synthetic scaffolds for applications in sustainable chemistry transformations. Nanoparticle-functionalised carbonaceous catalysts for new Fischer Tropsch and Reverse GasWater Shift (RGWS) transformations were prepared: functional graphene oxides emerged from graphite powders via an adapted Hummer's method and subsequently impregnated with uniform-sized nanoparticles. Then the resulting nanomaterials were imaged by TEM, SEM, EDX, AFM and characterised by IR, XPS and Raman spectroscopies prior to incorporation of Pd(II) promoters and further microscopic and spectroscopic analysis. Newly synthesised 2D and 3D layered nanostructures incorporating carbon-supported iron oxide nanoparticulate pre-catalysts were tested, upon hydrogen reduction in situ, for the conversion of CO₂ to CO as well as for the selective formation of CH₄ and longer chain hydrocarbons. The reduction reaction was also carried out and the catalytic species isolated and fully characterised. The catalytic activity of a graphene oxide-supported iron oxide pre-catalyst converted CO₂ into hydrocarbons at different temperatures (305, 335, 370 and 405 °C), and its activity compared well with that of the analogues supported on graphite oxide, the 3-dimensional material precursor to the graphene oxide. Investigation into the use of graphene oxide as a framework for catalysis showed that it has promising activity with respect to reverse gas water shift (RWGS) reaction of CO₂ to CO, even at the low levels of catalyst used and under the rather mild conditions employed at atmospheric pressure. Whilst the γ-Fe₂O₃ decorated graphene oxide-based pre-catalyst displays fairly constant activity up to 405 °C, it was found by GC-MS analysis to be unstable with respect to decomposition at higher temperatures. The addition of palladium as a promoter increased the activity of the iron functionalised graphite oxide in the RWGS. The activity of graphene oxide supported catalysts was found to be enhanced with respect to that of iron-functionalised graphite oxide with, or without palladium as a promoter, and comparable to that of Fe@carbon nanotube-based systems tested under analogous conditions. These results display a significant step forward for the catalytic activity estimations for the iron functionalised and rapidly processable and scalable graphene oxide. The hereby investigated phenomena are of particular relevance for the understanding of the intimate surface morphologies and the potential role of non-covalent interactions in the iron oxide-graphene oxide networks, which could inform the design of nano-materials with performance in future sustainable catalysis applications.