Fluorinated organometallics: Vinyl, alkynyl, allyl, benzyl, propargyl and aryl

Modular and Chemoselective Strategy for the Direct Access to α-Fluoroepoxides and Aziridines via the Addition of Fluoroiodomethyllithium to Carbonyl-Like Compounds

An expeditious, high-yielding synthesis of rare α-fluoroepoxides and α-fluoroaziridines through the addition of the unkown fluoroiodomethyllithium (LiCHIF)-formed via deprotonation the commercially available fluoroiodomethane with a lithium amide base-to carbonyl-like compounds is documented. The ring-closure reactions, leading to α-fluorinated three-membered heterocycles, rely on the diversely reactive C-I and C-F bonds. Excellent chemoselectivity was observed in the presence of highly sensitive functionalities-aldehyde, ketone, nitrile, alkene-which remained untouched during the homologation sequence.

Aryl-BIAN-ligated silver(i) trifluoromethoxide complex

The complex (Aryl-BIAN)AgOCF₃ has been synthesised and structurally characterised. The reactivity towards trifluoromethoxylation of benzyl bromides has also been examined.

Forming trifluoromethylmetallates: competition between decarboxylation and C-F bond activation of group 11 trifluoroacetate complexes, [CF3CO2ML]-

A combination of gas-phase 3D quadrupole ion trap mass spectrometry experiments and density functional theory (DFT) calculations have been used to examine the mechanism of thermal decomposition of fluorinated coinage metal carboxylates. The precursor anions, [CF(3)CO(2)MO(2)CCF(3)](-) (M = Cu, Ag and Au), were introduced into the gas-phase via electrospray ionization. Multistage mass spectrometry (MS(n)) experiments were conducted utilizing collision-induced dissociation, yielding a series of trifluoromethylated organometallic species and fluorides via the loss of CO(2), CF(2) or "CF(2)CO(2)". Carboxylate ligand loss was insignificant or absent in all cases. DFT calculations were carried out on a range of potentially competing fragmentation pathways for [CF(3)CO(2)MO(2)CCF(3)](-), [CF(3)CO(2)MCF(3)](-) and [CF(3)CO(2)MF](-). These shed light on possible products and mechanisms for loss of "CF(2)CO(2)", namely, concerted or step-wise loss of CO(2) and CF(2) and a CF(2)CO(2) lactone pathway. The lactone pathway was found to be higher in energy in all cases. In addition, the possibility of forming [CF(3)MCF(3)](-) and [CF(3)MF](-), via decarboxylation is discussed. For the first time the novel fluoride complexes [FMF](-), M = Cu, Ag and Au have been experimentally observed. Finally, the decomposition reactions of [CF(3)CO(2)ML](-) (where L = CF(3) and CF(3)CO(2)) and [CH(3)CO(2)ML](-) (where L = CH(3) and CH(3)CO(2)) are compared.

New preparation and synthetic reactions of 3,3,3-trifluoropropynyllithium, -borate and -stannane: facile synthesis of trifluoromethylated allenes, arylacetylenes and enynes

Background: Since trifluoromethyl-containing compounds have found diverse applications in the fields of pharmaceuticals and agrochemicals, facile and selective synthetic methods for trifluoromethyl-substituted compounds are an essential tool for advanced medicinal chemistry. Now that diverse synthetic transformations of carbon–carbon triple bonds are available, 3,3,3-trifluoropropynyl-substituted compounds serve as versatile building blocks for target molecules containing trifluoromethyl groups. Thus, novel synthetic methods and reagents for incorporation of a 3,3,3-trifluoropropynyl group into an organic compound have been the major concern in exploration and modification of fluorine-based biologically active substances. Results & discussion: We report a preparative method of 3,3,3-trifluoropropynyllithium and its reaction with electrophiles including aldehydes, ketones, trimethoxyborane, chlorosilanes and chlorostannanes in detail. Palladium-catalyzed synthetic reactions of the carbonyl adducts and the trifluoromethyl-containing metalloid reagents are also demonstrated, which provide simple synthetic methods of trifluoromethylated allenes, arylacetylenes and enynes. The synthetic transformations presented here expand the repertoire of trifluoromethylated compounds available for medicinal scientists and contribute to the advance of future medicinal chemistry.

A simple base-mediated halogenation of acidic sp2 C-H bonds under noncryogenic conditions

A new method has been developed for in situ halogenation of acidic sp(2) carbon-hydrogen bonds in heterocycles and electron-deficient arenes. Either selective monohalogenation or one-step exhaustive polyhalogenation is possible for substrates possessing several C-H bonds that are flanked by electron-withdrawing groups. For the most acidic arenes, such as pentafluorobenzene, K(3)PO(4) base can be employed instead of BuLi for metalation/halogenation sequences.

Modern synthetic methods for fluorine-substituted target molecules

Fluorine has come to be recognized as a key element in materials science: in heat-transfer agents, liquid crystals, dyes, surfactants, plastics, elastomers, membranes, and other materials. Furthermore, many fluorine-containing biologically active agents are finding applications as pharmaceuticals and agrochemicals. Progress in synthetic fluorine chemistry has been critical to the development of these fields and has led to the invention of many novel fluorinated molecules as future drugs and materials. As a result of the electronic effects of fluorine substituents, fluorinated substrates and reagents often exhibit unusual and unique chemical properties, which often make them incompatible with established synthetic methods. Thus, the problem of how to control the unusual properties of compounds with fluorine substituents deserves much attention, so as to promote the design of facile, efficient, and environmentally benign methods for the synthesis of valuable organofluorine targets.

Metal enolates ofα-CF3 ketones: theoretical guideline, direct generation, and synthetic use

The difficulty as well as the significance of the direct generation of metal enolates of alpha-CF(3) ketones cannot be easily understood by chemists unfamiliar with F. In sharp contrast to the sunny side of non-F, hydrocarbon chemistry, F chemistry has long been overshadowed. Metal enolates of carbonyl compounds are synthetically important in C-C bond-forming reactions. However, the metal enolates of fluorinated carbonyl compounds have been severely limited to alpha-F metal enolates. Alpha-CF(3) metal enolates have generally been recognized as unstable and difficult to prepare because of the facile beta-M-F elimination. However, we have developed a direct generation and synthetic application of alpha-CF(3) metal enolates. Therefore, the present results regarding the direct generation and synthetic use of metal enolates of alpha-CF(3) ketones might be recognized as a real breakthrough for the general use of metal enolates in F chemistry.

Preparation and Regioselective SN2‘ Reaction of Novel gem-Difluorinated Vinyloxiranes with RLi

A series of hitherto unknown 3,4-epoxy-1,1-difluorobutenes were prepared from the readily accessible alpha,beta-epoxy ketones and these compounds were found to undergo regioselective S(N)2' reactions with hard RLi nucleophiles occurring at the highly positively charged terminal fluorine-possessing sp(2) carbon atom in quite sharp contrast to the cases of the corresponding nonfluorinated vinyloxiranes which only attained a low level of regioselectivity. Addition of HMPA substantially improved the products' olefinic stereoselectivity. Theoretical calculations were used to qualitatively explore the nature of selectivity in these reactions.

A Unique Reaction Pathway of Fluorine-Substituted Ethyl Groups on Cu(111): Successive α,α-Fluoride Elimination

Fluorine-substituted ethyl groups on Cu(111) were generated by thermal scission of the C-I bond in the adsorbed C2F5I. Temperature-programmed reaction spectrometry observed a novel pathway resulting in the evolution of C4F6 above 400 K. Among the various isomers, this product was identified as hexafluro-2-butyne. Although abstraction of two fluorine atoms from the starting Cu-CF2CF3 was required, Cu-CCF3 (trifluoroethylidyne) was favored over Cu-CF=CF2 (trifluorovinyl) as the intermediate because this ethyl-ethylidyne-butyne pathway was suppressed on a Cu(100) surface devoid of the key threefold hollow binding sites for ethylidyne. Once formed, perfluoroethylidyne readily coupled to afford a tightly surface-bound hexafluoro-2-butyne up to 400 K. Therefore, the C-F bonds adjacent to the metal were found to be more susceptible to the bond activation, leading the chemisorbed perfluoroethyl to eliminate two F atoms successively from the alpha-carbon. This preference for alpha-elimination rather than beta-elimination (the most favorable route in hydrocarbons) may be quite general for metal surface-mediated reactions involving fluorinated alkyl groups.

Environmentally Benign Processes for Making Useful Fluorocarbons: Nickel- or Copper(I) Iodide-Catalyzed Reaction of Highly Fluorinated Epoxides with Halogens in the Absence of Solvent and Thermal Addition of CF2I2 to Olefins

Highly fluorinated epoxides react with halogens in the presence of nickel powder or CuI at elevated temperatures to provide a useful and general synthesis of dihalodifluoromethanes (CF(2)X(2)) and fluoroacyl fluorides (R(F)COF) in the absence of solvent. At 185 degrees C, hexafluoropropylene oxide and halogens produce CF(2)X(2) (X = I, Br) in 68-90% isolated yields, along with small amounts of X(CF(2))(n)()X, (n = 2, 3). With interhalogens I-X (X = Cl, Br), a mixture of CF(2)I(2), CF(2)XI, and CF(2)X(2) was obtained. The fluorinated epoxides substituted with perfluorophenyl, fluorosulfonyl, and chlorofluoroalkyl groups also react cleanly with iodine to give CF(2)I(2) and the corresponding fluorinated acyl fluorides in good yields. The reaction probably involves an oxidative addition of fluorinated epoxides into metal surfaces to form an oxametallacycle, followed by rapid decomposition to difluorocarbene-metal surfaces, which alters the reactivity of the difluorocarbene carbon from electrophilic to nucleophilic. The increase of nucleophilicity of difluorocarbene facilitates the reaction with electrophilic halogens. CF(2)I(2) reacted with olefins thermally to give 1,3-diiodofluoropropane derivatives. Both fluorinated and nonfluorinated alkenes gave good yields of the adducts. Reaction with ethylene, propylene, perfluoroalkylethylene, vinylidene fluoride, and trifluoroethylene provided the corresponding adducts in 58-86% yields. With tetrafluoroethylene, a 1:1 adduct was predominantly formed along with small amounts of higher homologues. In contrast to perfluoroalkyl iodides, CF(2)I(2) also readily adds to perfluorovinyl ethers to give 1,3-diiodoperfluoro ethers.

Highly-functionalised difluorinated (hydroxymethyl)conduritol analogues via the Diels-Alder reactions of a difluorinated dienophile

A difluorodienophile, synthesised using a Stille coupling reaction underwent tin(iv)-catalysed cycloaddition with three furans to afford oxa[2.2.1]bicycloheptenes in good yield. Reduction of ester and carbamate carbonyl groups and diol protection as the acetonide set the stage for palladium-catalysed hydrostannylation in two cases. Treatment of the stannanes with methyllithium triggered ring-opening to afford highly-functionalised difluorinated cyclohexenols which could be deprotected to afford (hydroxymethyl)conduritol analogues.