Trifluoromethylation free-radical

There have been several reports of the formation of tertiary bismuthines by the action of free radicals on metallic bismuth. One method of generating the radicals iavolves cleavage of ethane or hexafluoroethane ia a radiofrequeacy glow discharge apparatus the radicals thus formed are allowed to oxidize the metal at — 196°C (53). Trimethylbismuthiae and tris(trifluoromethyl)bismuthine [5863-80-9], C BiF, have been obtained by this procedure. 

Guanine, 9-/3-D-ribofuranosyl-, 5, 536 Guanine, 6-thio-tautomerism, 5, 509 toxicity, 1, 141 Guanine, 8-trifluoromethyl-synthesis, 5, 574 Guanines, thio-synthesis, 5, 572 Guanosine arylation, 5, 538 dipole moment, 5, 522 free radical alkylation, 5, 543 hydrobromide... 

The investigated cw-stilbene derivatives, 4-methoxy, 4,4 -dimethyl, unsubstituted, and 4,4 -bis(trifluoromethyl)stilbenes, had k2 values spanning 6-7 powers of ten both in methanol and in acetic acid. Products 2, 4, 5 and 6 were formed. Table 8 reports the results of the cis-trans isomerization test in acetic acid (ref. 29). No acid catalyzed or free radical process was found to be responsible for these isomerizations. 

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

In the presence of copper(I) chloride, FC-113a adds to silyl enol ethers affording adducts which can be transformed into the /1-chloro-/i-trifluoromethyl enones in moderate yields [100]. The carbon-carbon bond is formed via a free radical addition reaction (Eq. 28). Free radical addition mediated by iron pentacarbonyl was also described recently during a synthesis of a modified pyrethroid [101]. 

The precursor was prepared via a lengthy sequence involving the elaboration of a Reformatsky adduct. The cyclic product was obtained as a 1.2 1 mixture of cis and trans isomers.The presence of the fluorine atoms had no effect on the efficiency of the cyclisation reaction. A subsequent study [384] extended the range of cyclisations to include trifluoromethyl alkyl and alkenyl radicals (Eq. 157). Free radical cyclisation reactions therefore show considerable promise for the rational synthesis of fluorinated carbocycles. 

Styrene and 1,1-diphenylethene are frequently used as target molecules in investigations of the role of reagent structure on its reactivity toward organic compounds. Low-temperature fluorination with trifluoromethyl hypofluorite gives up to six products.32-33 The Hammett correlation value q was established to be — 2.48 and a mechanism suggested in which spin-paired free-radical pairs arc formed, which are then converted by electron transfer into an ion pair.33... 

V,/V-Bis(trifluoromethyl)hydroxylamine (5) is oxidized with potassium permanganate in acetic acid to an interesting free-radical compound, bis(trifluoromethyl)nitroxid-A7-yl(6), a pink-violet gas which condenses to a deep brown-violet liquid.246 Various oxidizing agents are effective in the oxidation of 5 to the corresponding nitroxyl 6.247 The best appears to be cerium(IV) salts either in the solid state or in aqueous acid solution.247 Efficient oxidation processes have been developed using aqueous potassium persulfate solutions, or electrochemical oxidation with cerium(III) nitrate and sodium nitrate in dilute nitric acid.247... 

ESR spectroscopy is perhaps the best method for the unequivocal detection and observation of free radicals, and ESR 13C hyperfine splitting (hfs) constants are considered to be a very useful indicator of a radical s geometry because non-planarity introduces s character into the orbital that contains the unpaired electron. The methyl radical s 13Ca value of 38 G is consistent with a planar structure. Fluoromethyl radicals exhibit increased 13Ca values, as shown in Table 1, thus indicating increasing non-planarity, with trifluoromethyl radical s value of 272 G lying close to that expected for its sp3 hybridization [4]. 

Reactions of bis(trifluoromethyl)nitroxyl with a number of methyl-and trifluoromethyl-substituted arsanes at room temperature give compounds of type Me3-n(CF3)nM[ON(CF3)2]2 (n = 0,1, 2) (6, 7). A free radical mechanism has been proposed for these oxidative addition reactions. 

Incorporation of the trifluoromethyl thiol moiety into heterocyclic systems may be achieved by several methods (92T6633). Trifluoromethylthio-lation of heteroaromatic compounds with trifluoromethansulfenyl chloride occurs via a free radical chain mechanism (77CB67) (Scheme 17). 

Four perfluorodiacylperoxide free radical initiators were prepared by condensing perfluoroacyl chloride derivatives with hydrogen peroxide and sodium hydroxide. When the product bis(2-fluoro-2-trifluoromethyl-perfluoropropionyl) peroxide was used to polymerize vinylidene fluoride, a 90% conversion was observed. 

Of a large number of possible fluorinated acrylates, the homopolymers and copolymers of fluoroalkyl acrylates and methacrylates are the most suitable for practical applications. They are used in the manufacture of plastic lightguides (optical fibers) resists water-, oil-, and dirt-repellent coatings and other advanced applications [14]. Several rather complex methods to prepare the a-fluoroalkyl monomers (e.g., a-phenyl fluoroacrylates, a-(trifluoromethyl) acrylic and its esters, esters of perfluoromethacrylic acid) exist and are discussed in some detail in [14]. Generally, a-fluoroacrylates polymerize more readily than corresponding nonfluorinated acrylates and methacrylates, mostly by free radical mechanism [15], Copolymerization of fluoroacrylates has been carried out in bulk, solution, or emulsion initiated with peroxides, azobisisobutyronitrile, or y-irradiation [16]. Fluoroalkyl methacrylates and acrylates also polymerize by anionic mechanism, but the polymerization rates are considerably slower than those of radical polymerization [17]. 

Among the simple transient species of carbon and fluorine are included trifluoromethyl cation, CF3+, which has a very transient existence trifluoromethyl anion, CF3, which is stable at low temperature and can be generated from CF3TMS (trimethylsilyltrifluoromethane) CF3-, a free radical available from irradiation of CF3I and difluorocarbene, CF2 , which exists as a ground-state singlet. 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

In a series of papers, Itoh and Mikami have reported the high yield, radical a-trifluoro-methylation of ketones using titanium euolates and Mefl/BEts as free radical generator and trifluoromethylating agent . The use of excess Ida and Ti(OPr-/)4 in the preparation of the titanium euolate represeuts the key to the success of the reaction (equation 41). Interest in this reaction stems from the fact that in general, the radical a-trifluoromethylation of ketones via lithium enolates is complicated by the easy defluorination of the a-CFs ketone by the parent enolate . For this reason, less reactive enolates such as silyl or germyl enolates have been initially used instead of lithium enolates" . 

More recently Ito and Mikami observed" that the titanium reagent is not indispensable in the case of highly basic lithium enolates derived from cyclic ketones or silyl enolates, for which the reactions are very fast (ending in ca Is to 5 min) and afford high yields of the a-trifluoromethylation products. A tentative radical mechanism has been proposed for these processes" involving reaction of the Mef free radical with the enolate to give a radical intermediate which reacts with another MefI molecule to afford Mef and the a-trifluoromethylation product (equation 42). 

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