Fluorinated alkenes synthesis

On the other hand, fluorinated olefins are used as intermediates for fluorinated polymers. A growing effort is currently being performed to set out cleaner processes for these latter compounds. To achieve an environmentally sustainable process, a possible alternative for fluorinated alkenes synthesis is the reaction of olefins with fluorinated solids. 

Fluorinated alkenes and alkynes are highly activated toward nucleophilic attack and reaction with bifunctional nucleophiles is a fruitful area for the synthesis of heterocycles. A review on perfluoroalkyl(aryl)acety-lenes contains many examples (91RCR501). 

The usual reaction of alkenes with conjugated dienes is the Diels-Alder synthesis. This addition does not apply, with a few exceptions, to cycloaddition of fluorinated alkenes. The presence of fluorine atoms, especially if there are more of them around the double bond, retards the cycloadditions forming six-membered rings, and accelerates the (2 + 2) cycloaddition to form four-membered rings. 

Synthesis of Fluorinated Alkenes through Halogen Exchange... 

The synthesis of fluorinated cyclopropanes has been achieved via the addition of fluorinated carbenes to alkenes and via the addition of nonfluorinated carbenes to fluorinated alkenes. 

Several perfluoroalkene derivatives have been made and used successfully in synthesis. Trifluorovinylmagnesium bromide and the lithium derivative may be obtained [39 1] from bromotrifluoroethene but preparation from HFC 134a, which involves metallation of trifluoroethene generated in situ, is now the more accessible route (see Section lA). However, direct metallation of fluorinated alkenes and fluorinated cycloalkenes has also been reported [26, 28] (Figure 10.9). 

Perfluorinated alkyl iodides are very important intermediates for the synthesis ofperfluoroalkyl-substituted compounds. They can be prepared by addition of fluorine and iodine to fluorinated alkenes. This addition can be carried out with various sources of IF" fluorine/iodine,225 226 hydrogen fluoride/iodine,190-297"308-313-31 5 potassium fluoride/iodine,l88-293 294-299 iodine pentafluoride/iodine,168 187-208 230 233 235-230 242-293-295 296-30 302-307 or iodine trifluoridc/ iodine.208-305... 

The initial studies of Horvdth and Rabai were concentrated on the synthesis of the fluorinated trialkylphosphane 12 which is a suitable ligand for many transition metals [4,17]. This phosphane was prepared by a hydrophosphination of the corresponding fluorinated alkene 13 Eq. (7). 

Very recently, a different synthetic approach to fluorinated p-lactams involving catalytic hydrogenolysis of the N-O bond of isoxazohdines appeared in the literature. The method involves the synthesis of isoxazohdines (71) by 1,3-cycloaddition of aromatic nitrones to fluorinated alkenes, followed by N-O bond cleavage by hydrogenolysis using palladium catalyst (Scheme 2.34). ... 

Sekiya A, Shibakami M, Tamura M. 1995. Potassium fluoride-poly (hydrogen fluoride) salts as fluorinating agents for haofluorination of alkenes. Synthesis 5 515-517. 

Besset T, Poisson T, Pannecoucke X (2015) Direct vicinal difunctionalization of alkynes an efficient approach towards the synthesis of highly functionalized fluorinated alkenes. Eur J Org Chem 13 2765-2789... 

The introduction of a fluorine atom to bioactive compounds can modify their activity, so much effort has been invested in the development of selective fluorination reactions. Many bioactive compounds that have double bonds are known, and their analogs, which have a fluorine atom at their double bond, have been attracting the attention of biochemists and organic chemists [ 1 -4-]. In order to induce an effect on the activity of bioactive compounds, a fluorine atom must be introduced to the desired position at the double bond with the correct stereochemistry. The stereoselective synthesis of fluoroalkene is therefore important. There have been articles written recently that concern fluoroalkene synthesis [5-7] so I would like to introduce the recent development in the stereoselective synthesis of mono-fluorinated alkenes. 

Zhu LG, Ni CF, Zhao YC, Hu JB. 1-tert-Butyl-lH-tetrazol-5-yl fluoromethyl sulfone (TBTSO2CH2F) a versatile fluo-romethylidene synthon and its use in the synthesis of mono-fluorinated alkenes via Julia-Kocienski olefination. reiraAefi roM2010 66(27-28) 5089-5100. 

The first synthesis of saturated hydrofluoroethers was realized in 2005, through the addition of various alcohols to a fluorinated alkene in the presence of Pd(PPh3)4 under neutral conditimis, at room temperature. With poor acidic alcohols, catalytic activity was increased in the presence of cocatalytic l,4-bis-(diphenylphosphino) butane (dppb) [90] (Scheme 43). 

The synthesis of 2-chloro-2,3,3-trifluorocyclobutyl acetate illustrates a general method of preparing cyclobutanes by heating chlorotrifluoroethylene, tetrafluoroethylene, and other highly fluorinated ethylenes with alkenes. The reaction has recently been reviewed.11 Chlorotrifluoroethylene has been shown to form cyclobutanes in this way with acrylonitrile,6 vinylidene chloride,3 phenylacetylene,7 and methyl propiolate.3 A far greater number of cyclobutanes have been prepared from tetrafluoroethylene and alkenes 4,11 when tetrafluoroethylene is used, care must be exercised because of the danger of explosion. The fluorinated cyclobutanes can be converted to a variety of cyclobutanes, cyclobutenes, and butadienes. 

Tho main routes for the insertion of fluorinated alkyl groups in the silicones are suggested either by organometallic or by hydrosilylation methods as shown in Scheme 2. Consequently, research can be pursued in two directions (a) synthesis of fluorohalides and alkenes, and (b) introduction in siliconated groups and polymerization. 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

Bromo [ F]fluoride (Section 3.9.1) addition across a double bond was used in the synthesis of fluorine-18-labelled steroids of high specific radioactivity. After addition, the bromine is removed by reduction or by dehydrobromination. [ F]Fluoro-5a-dihydrotestosterone was obtained in about 3% radiochemical yield (Scheme 17) [64] and 6a-p F]fluoroprogesterone in only 0.3% [65]. The yields were quite low but sufficient to allow for animal studies. These reactions had been tested out successfully with simpler model alkenes [66]. 

Fluorine is used for the fluorination of sites x to sulfoxides with simultaneous oxidation of the sulfoxide moiety to a sulfone. The electrophilic fluorine attacks the electron lone pairs of the sulfur atom with a consequent loss of hydrogen fluoride forming an S-fluorosulfoxy alkene. A second molecule of fluorine adds across the newly formed double bond resulting, after hydrolysis, in an a-fluoro sulfone 12.88 This reaction is used for the construction of a fluorocy-clopropane derivative 13 which is essential in the synthesis of one of the most promising members of the quinolinecarboxylic acid antibiotics.89... 

Due to their industrial applications, tetrafluorooxirane and perfluoro(2-methyloxirane) are the most frequently mentioned epoxides in the literature, and a number of methods have been developed for their synthesis. Although the epoxidation of perfluoroalkenes with hydrogen peroxide in alkaline media appears to be the most general method for the synthesis of per-fluorinated epoxides, it cannot be used in the preparation of tetrafluorooxirane due to the hydrolytic decomposition of the alkene. 

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