Of fluoroalkenes

The direct oxidation of fluoroalkenes is also an excellent general synthesis procedure for the preparation of perfluoroepoxides (eq. 8). This method exploits the low reactivity of the epoxide products to both organic and inorganic free radicals. 

Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

JV-Fluoro-Z -t-butylbenzenesulfanamide (Table 3a, A) reacts with t iny/lithium reagents prepared from lodoalkenes to give high yields of fluoroalkenes with higli stereoselectivity [84] (Table 4)... 

Ozonuies (1,2,4-trioxolanes) are generally obtained by the reaction of fluoroalkenes with ozone Thus, vmyl fluonde is oxidized to monofluoroozomde and formyl fluonde [23] (equation 15) The same ozomde is formed by ozonolysis of a mixture of cis 1,2-difluoroethylene with ethylene [24]... 

Fluorinated cyclobutanes and cyclobutenes are relatively easy to prepare because of the propensity of many gem-difluoroolefins to thermally cyclodimerize and cycloadd to alkenes and alkynes. Even with dienes, fluoroolefins commonly prefer to form cyclobutane rather than six-membered-ring Diels-Alder adducts. Tetrafluoroethylene, chlorotrifluoroethylene, and l,l-dichloro-2,2-difluoroethyl-ene are especially reactive in this context. Most evidence favors a stepwise diradical or, less often, a dipolar mechanism for [2+2] cycloadditions of fluoroalkenes [S5, (5], although arguments for a symmetry-allowed, concerted [2j-t-2J process persist [87], The scope, characteristic features, and mechanistic studies of fluoroolefin... 

The differences in the steric effect between catecholborane and pinacolborane, and the valence effect between a cationic or neutral rhodium complex reverse the re-gioselechvity for fluoroalkenes (Scheme 1-4) [26]. The reaction affords one of two possible isomers with excellent regioselectivity by selecting borane and the catalyst appropriately, whereas the uncatalyzed reaction of 9-BBN or SiaiBH failed to yield the hydroboration products because of the low nucleophilicity of fluoroalkenes. The regiochemical preference is consistent with the selectivity that is observed in the hydroboration of styrene. Thus, the internal products are selectively obtained when using a cationic rhodium and small catecholborane while bulky pinacolborane yields terminal products in the presence of a neutral rhodium catalyst. 

Ring current (anisotropic) effects do not play a significant role in fluorine NMR. Therefore, fluorine substituents on a benzene ring absorb in the general region of fluoroalkenes, with fluorobenzene and 1-fluoronaphthalene having chemical shifts of -113.5 and -123.9 ppm, respectively. The fluorine NMR of fluorobenzene is shown in Fig. 3.14. 

For the synthesis of the title compound, Oxone or 3-chloroperbenzoic acid2 can be used to oxidize the sulfide to the sulfone. The title compound is a key reagent for the preparation of fluoroalkenes from aromatic11 and aliphatic2 aldehydes. Recently, a stereospecific method to (E)- and (Z)-fluoroalkenes was reported using this reagant.12 13 14... 

REACTION OF SULFOXIDES WITH DIETHYLAMINOSULFUR TRIFLUORIDE PREPARATION OF FLUOROMETHYL PHENYL SULFONE, A REAGENT FOR THE SYNTHESIS OF FLUOROALKENES (Benzene, [(fluoromethyl)sulfonyl]-)... 

The procedure described here provides a stereospecific synthesis of (E)- and (Z)-fluoroalkenes from the corresponding (E)- and (Z)-fluorovinyl sulfones. Fluorovinyl sulfones obtained from ketones are, in most cases, readily separable into (E) and (Z) isomers either by crystallization or by chromatography.4 In the example described, only the (E)-fluorovinyl sulfone 1 is formed (which is converted into the (Z)-fluoroalkene 3 with complete retention of configuration). The reaction sequence has been used for the stereospecific synthesis of fluoroalkene nucleosides5 as well as for... 

Hydration of olefins, alkynes and nitriles calls explicitely for the use of aqueous solvents. Indeed, one of the earliest investigations originates from 1969, when hydration of fluoroalkenes were studied with Ru(II)-chloride catalysts (Scheme 9.6). The reaction has no synthetic value but the studies helped to clarify the mechanism of the interaction of olefins with Ru(II)... 

The thermal cyclodimerization of fluoroalkenes represents a route to fluorinated cyclobutanes. In most cases the neat alkene is heated in a sealed tube for prolonged periods of time. For symmetrical fluoroethenes head-to-head dimerization predominates. For instance, 1.1-dichloro-2,2-difluoroethene (1) undergoes thermal dimerization (180°C, 14 days) to give the hcad-to-hcad dimer 2 although no yield was reported.1... 

Since the seminal work of Bartlett [363] there have been relatively few reports of useful cycloadditions of fluoroalkenes. Recent work by Haufe showed that fluorine atom substituents depress the reactivity of styrene derivatives in the Diels-Alder reaction with 1,3-diphenylisobenzofuran. A single fluorine atom in the /1-position lowered the rate of the [4 + 2] reaction by a factor of ten when the fluorine atom occupied the -position (Eq. 142), the reaction was over 30 times slower than that of the unsubstituted styrene. 

Stansfield (1996) Diels-Alder Reactions of Fluoroalkenes New Strategy and Tactics in... 

More often, however, fluorocarbanions are intermediates in reactions of fluoroalkenes,35 e.g. by addition of nucleophiles, especially fluoride. Deprotonation of hydrofluorocarbons also yields the anion. Whereas a-fluorination destabilizes the anion, /J-fluorination is essentially stabilizing. The latter effect may be assisted by so-called fluorine-nonbond resonance (negative anionic hyperconjugation) which has been discussed in diverse ways supported by some,3 but criticized by others.2 31... 

Fluorinated radicals play a significant role in synthetic organo-fluorine chemistry, for example, in electrophilic radical addition to alkenes, single-electron transfer reactions (SET), telomerization of fluoroalkenes with perfluoroalkyl iodides, polymerization to fluoropolymers and copolymers, and thermal, photochemical and radiation destruction of fluorocarbons. Furthermore, such free radicals are of interest for studying structures, reaction kinetics and ESR spectroscopic parameters.38... 

An intensive study of fluoroalkenes was initiated by the Environmental Protection Agency (EPA) in 1981.3,1 In addition to acute toxicities, a lot more toxic information is included in recent literature.34 36 Metabolic studies of alkenes, acting as nephrotoxins have been reported.37... 

The direction of iodine monofluoride addition to hexafluoropropene and, 1,1-di-fluoroethene suggests an electrophilic reaction mechanism. However, chlorotrifluoroethene gives a mixture of isomers both with iodine monofluoridc and with bromine monofluoride .1 0 The reactions of fluoroalkenes with bromine monofluoride proceed too quickly and for this reason they are conducted in l,l,2-trichloro-l,2,2-trifluoroethane though this hampers the isolation of addition products. 

Fluorination of fluoroalkenes with terminal C = C bonds with vanadium(V) fluoride proceeds readily at —30 to — 25 C in trichlorofluoromelhane solution. The only reaction products are the corresponding polyfluoroalkanes formed in high yields.117... 

The reaction of fluoroalkenes with nickel(O) phosphine and arsine complexes may also result in the dimerization of the fluoroalkene and in the formation, for example, of octafluoro-nickelacyclopentane complexes [Ni(ER3)2(CF2)4] (E = P, As), which contain the nickel atom in the formal oxidation state +2., 55 A similar reaction also occurs when [N PPhj QtFj reacts... 

Bis(trifluoromethyl)nitroxyl readily attacks the C = C bond of fluoroalkenes. Two radicals add across the C = C bond95-97 to give the corresponding vicinal bis[bis(trifluoromethyl)amino-oxy]alkanes 60 in 80% to quantitative yields. Even fluoroaromatic compounds react in the same way (vide infra). 

It has been shown in ozonizations of fluoroalkenes (vide supra) that fluoro substituents stabilize the ozonides formed from the rearrangement of the initial molozonides. Rather stable ozonide isomers 3 are formed from the trifluoromethylated alkenyl ether 2 as two separable dia-stereomers with isolated yields 27 and 26%. respectively.180 The stability was demonstrated... 

The regioselectivity in reactions of fluoroalkenes to maximize the number of fluorines in the /f-position illustrates that whether hyperconjugative interactions are important or not, fluorine in the /i-position can have a profound effect on the outcome of reactions.75,81,82... 

Fluorine is simultaneously eliminated with other halogens if it is the only halogen vicinal to iodine, bromine or chlorine. The elimination tendency decreases in the series IF > BrF > C1F. The group CF2CHFX is relatively stable towards elimination and requires stronger reaction conditions. The dehalogenation of saturated fluorohalo compounds with zinc dust or zinc/ copper and zinc/silver couples is one of the most useful methods for the preparation of fluoroalkenes (see Table 8). Zinc/zinc(II) chloride has also been used instead of zinc alone. 

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