Fluoroolefins reactions, nucleophilic

A fluormated enol ether formed by the reaction of sodium ethoxide with chlorotnfluoroethylene is much less reactive than the starting fluoroolefin To replace the second fluorine atom, it is necessary to reflux the reaction mixture. The nucleophilic substitution proceeds by the addition-elimination mechanism [30] (equation 26). 

Fluonnated ylides have also been prepared in such a way that fluonne is incorporated at the carhon P to the carbamonic carbon Vanous fluoroalkyl iodides were heated with tnphenylphosphine in the absence of solvent to form the necessary phosphonium salts Direct deprotonation with butyUithium or hthium dusopropy-lamide did not lead to yhde formation, rather, deprotonation was accomparued by loss of fluonde ion Flowever deprotonation with hydrated potassium carbonate in thoxane was successful and resulted in fluoroolefin yields of45-S0% [59] (equation 54) P-Fluorinated ylides may also be prepared by the reaction of an isopropyli-denetnphenylphosphine yhde with a perfluoroalkanoyl anhydnde The intermediate acyl phosphonium salt can undergo further reaction with methylene tnphenylphosphorane and phenyUithium to form a new yhde, which can then be used in a Wittig olefination procedure [60] (equation 55) or can react with a nucleophile [6/j such as an acetyhde to form a fluonnated enyne [62] (equation 56)... 

Phenylmercury halides give the corresponding phenylmercury derivative, CgH5HgC(CF3)3 (61%) [156], and perfluorocyclobutene gives the corresponding cyclobutyl derivative [156], Mechanistically, the reaction could be interpreted as formation of the fluorocarbanion via nucleophilic addition of fluoride ion to the fluoroolefin followed by capture of the intermediate fluorocarbanion by the mercury salt [156]. The regiochemistry of the reaction is consistent with this mechanism [156] (equation 119). 

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

The addition of nucleophiles to cyclic fluoroolefins has been reviewed by Park et al. [2 ]. The reaction with alcohols proceeds by addition-elimination to yield the cyclic vinylic ether, as illustrated by tlie reaction of l,2-dichloro-3,3-di-fluorocyclopropene Further reaction results in cyclopropane ring opening at the bond opposite the difluoromethylene carbon to give preferentially the methyl and ortho esters of (Z)-3-chloro-2-fluoroacrylic acid and a small amount of dimethyl malonate [29] (equation 8). 

The addition of primary amines to fluoroolefins under anhydrous conditions yields imines The hexafluoropropene dimer, perfluoro-2-methyl-2-pcntcne, and ten butylamine react to yield a mixture of two compounds m a 9 4 ratio [4] (equation 3) rather than just the major keteiiimme-imine, as previously reported [5] It IS claimed that this result is possible by means of isomerization to the terminally unsaturated difluoromethylene isomer prior to nucleophilic attack Secondary amines add to fluoroolefins under anhydrous conditions to give fluonnated ternary amines m good yields If the fluoroolefin is added to the amine without cooling the reaction mixture, or if an excess of the secondary armne is used, there is a tendency toward dehvdrofluonnation of the ternary amine The products... 

Fluoride ion produced from the nucleophilic addition-elimination reactions of fluoroolefins can cataly7e isomerizations and rearrangements The reaction of per fluoro-3-methyl-l-butene with dimethylamine gives as products 1-/V,/Vdimeth-ylamino-1,1,2,2,4,4,4-heptafluoro-3-trifluoromethylbutane, N,W-dimetliyl-2,2,4,4,4-pentafluoro 3 trifluoromethylbutyramide, and approximately 3% of an unidentified olefin [10] The butylamide results from hydrolysis of the observed tertiary amine, and thus they share a common intermediate, l-Al,A -dimethylamino-l,l 24 44-hexafluoro-3-trifluoromethyl-2-butene, the product from the initial addition-elimination reaction (equation 4) The expected product from simple addition was not found... 

Today microemulsions are used in catalysis, preparation of submicron particles, solar energy conversion, extraction of minerals and protein, detergency and lubrication [58]. Most studies in the field of basic research have dealt with the physical chemistry of the systems themselves and only recently have microemulsions been used as a reaction medium in organic synthesis. The reactions investigated to date include nucleophilic substitution and additions [59], oxidations [59-61], alkylation [62], synthesis of trialkylamines [63], coupling of aryl halides [64], nitration of phenols [65], photoamidation of fluoroolefins [66] and some Diels-Alder reactions. 

Miller et al. [9] hypothesized rules on the regioselectivity of addition from the study of the base-catalyzed addition of alcohols to chlorotnfluoroethylene. Attack occurs al the vinylic carbon with most fluorines. Thus, isomers of dichloro-hexafluorobutene react with methanol and phenol to give the corresponding saturated and vinylic ethers The nucleophiles exclusively attack position 3 of 1,1-dichloro-l,2,3,4,4,4-hexafluoro-2-butene and position 1 of 4,4-dichloro-l,l,2,3,3,4-hexafluoro-1-butene [/0]. In l,l-dichloro-2,3,3,4,4,4-hexafluoro-l-butene, attack on position 2 is favored [1I (equation 5) Terminal fluoroolefins are almost invariably attacked at the difluoromethylene group, as illustrated by the reaction of sodium methoxide with perfluoro-l-heptene in methanol [12 (equation 6). 

The reactivity and orientation of nucleophilic attack on fluoroolefins are determined by the stability of the possible carbamon intermediates Fluoroolefins react regioselectively with nucleophiles so as to maximize the number of fluorines (3 to the electron-rich carbon in the transition state The reactivities increase in the order CF2=CF2 < CF2=CFCF3 CF2=C(CF3)2 and CF2=CF2 < CF2=CFC1 < CF2=CFBr, and nucleophdes attack exclusively at the CF2= end of these olefins [129,141] The regiochemistry of nucleophilic attack normally is predictable, but the product distribution arising from addition and addition-elimination pathways depends upon the olefin, nucleophile, and reaction conditions (equations 13-15) The various factors that control product distributions have been reviewed [142,143 144]... 

Pyridine-l-oxide and some of its ring-substituted derivatives act as nucleophiles and generally give the corresponding 2-(l,2,2,2-tetrafluoro)pyndmes upon reaction with hexajluoropropene [21,22]. The reaction involves a novel rearrangement, as illustrated in the proposed mechanism (equation 10 and Table 1) Initial attack of the fluoroolefin by the oxygen produces an intermediate 1,5 dipole, followed by collapse and extrusion of carbonyl fluoride... 

Pentafluorophenylation of the fluoroolefin T-2 with C6FsSi(CH3)3 (lb) proceeded in an aprotic solvent in the presence of catalytic fluoride anion, similarly to the reaction of T-2 with la however, successive nucleophilic attacks of lb on the QFs ring were also observed (Scheme 2) [9]. 

The fluoropyridazines have been intensively investigated by Musgrave and co-workers. Earlier work or nucleophilic substitutions in perfluoro-pyridazines has been reviewed. Tetrafluoropyridazine reacts with hexa-fluoropropene to give products formed from both kinetic and thermodynamic control of the polyfluoroalkylation, i.e., the fluoride ion-induced reaction between a fluoroolefin and an activated polyfluoroaromatic compound. The reaction with tetrafluoroethylene is kinetically controlled. Products arising only from thermodynamic control are formed, however, in the reaction with octafluoroisobutene. 

Mechanistically, this process is similar to the cyclization processess involving fluoroolefins 16 and 24. The reaction involves the attack of nitrogen on the electron-deficient C=N double bond of 44 with the migration of the double bond, followed by a ring closure step via intramolecular nucleophilic displacement of fluorine in the CF=N- unit by alkoxy anion. The formation of 45 containing two C=N double bonds is the result of HF abstraction by triethylamine (Fig. 10.19). 

As a candidate for a polymer-forming process, reactions with fluoroolefins seemed the most promising. As discussed earlier, fluorinated olefins react readily with many nucleophilic species. These acceptors react with RfSiMea to give either mono- or bis(perfluoroalkylated) products (Scheme 8). Product specificity is enhanced for cyclic olefins whose higher reactivity and thermodynamically uphill isomerization pathways account for this tendency. 

Figure 2.4 Proposed reaction scheme for nucleophilic attack on fluoroolefins. ...

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