Fluorination, of alkenes

In the fluorination of alkenes with a terminal double bond, a significant amount of trifluoro compound was produced. This is believed to occur by the loss of H+ from the cationic intermediate followed by addition of fluorine to the resulting double bond (Fig. 74). 

Acetyl hypofluorite appears to be a milder reagent than trifluoroacetyl hypofluorite in the fluorination of alkenes and acetylenes. Acetyl hypofluorite undergoes addition to the C = C bond in the fluorination of cyclohexene the ij f7-adduct 4 is obtained in 60% yield, while the reaction with dodec-l-ene gives 2-acctoxy-l-fluorododccanc (5) in 30% yield.10... 

Fluorination of Alkenes 2 by Cesium Fluoroxysulfate (NuH =. YleOH) General Procedure 8... 

The fluorination of alkenes with XeF2 has been reviewed.582 Furthermore, PhTeF5 and PhSeF5 have been shown to be powerful difluorinating reagents.583... 

Xenon difluoride [4, 5, 7, 8,10] is a white crystalline material obtained through the combination of fluorine and xenon in the presence of light The reagent is commercially available and possesses a relatively long shelf-life when stored cold (freezer) Xenon difluoride is very effective for small-scale fluorination of alkenes and activated nucleophilic substrates. The reactions are usually conducted between 0 °C and room temperature in chloroform or methylene chloride solutions Hydrogen fluoride catalysis is sometimes helpful Xenon difluoride reacts m a manner that usually involves some complexation between the substrate and reagent followed by the formation of radical and radical cation intermediates... 

Fluorination of alkenes.1 Fluorination of some aliphatic alkenes with 1 has been reported. 

As in the case of the fluorination of alkenes in methanol, reaction with 1,3-dienes depends strongly on the catalyst used, and five products were formed by reaction of 2,3-dimethyl-1,3-butadiene when hydrogen fluoride or boron trifluoride were used as catalysts83 (Scheme 27). 

Fluorination of Alkenes with Xenon Fluorides General Procedure " ... 

The electrochemical fluorination of alkenes in anhydrous hydrogen fluoride is another possibility for the addition of fluorine to unsaturated compounds, but the yields are poor to moderate and the difluoro addition products are only byproducts. 

Fluorination of Alkenes with Cesium Fluoroxysulfate in Methanol General Procedure ... 

Fluorination of alkenes. The reagent adds in the Markownikofl fashion to alkenes to yield alkyl fluorides (35-90% yield). It converts secondary and tertiary alcohols into the corresponding alkyl fluorides. In situ diazotization followed by dediazotization converts a-amino acids into a-fluorocarboxylic acids (38-98% yield). The reagent converts acid chlorides and anhydrides into acid fluorides. ... 

Evidence has been presented that hypofluorites (see Section IIIB) can act as sources of electrophilic fluorine for reactions with electron-rich double bonds [11, 93]. Syn addition usually occurs and a tight ion-pair intermediate similar to that postulated to occur in the direct fluorination of alkenes can be envisaged. However, electron-transfer processes have been invoked [93] to explain some anomalous results and cannot be discounted [281] (Figure 3.64). 

Nonfluorinated alkyl hypofluorites (ROF) are mostly unstable and decompose through HF elimination with formation of the corresponding carbonyl compounds. However, tert-butyl [24] and methyl hypofluorites (RO+ F ) [25] can be generated and employed in situ for alkoxy-fluorination of alkenes. The relatively higher stability of both hypofluorites comes from the nonavailability of a-hydrogens which are reactive to the radical hydrogen abstraction [26]. Both of the hypofluorites add to carbon-carbon double bonds regio- and stereoselectively as shown in Scheme 2.48. The anti-addition mode (37-39) is in sharp contrast to the syn-addition mode of electrophilic fluoroalkoxy and acetoxy reactions of fluorinated alkyl and acetyl hypofluorites (RfO F+, 40-41) [27]. 

The fluorination of alkenes 41 and 43 and alkynes 45 with difluoroiodotoluene in the presence of iodine affords vt c-fluoroiodoalkanes 42 and 44 and fluoroiodoalkenes 46 in moderate to good yields (Scheme 3.16) [40]. This reaction proceeds in a Markovnikov fashion and with prevalent an//-stereoselectivity via initial addition of the electrophilic iodine species followed by nucleophilic attack of fluorine anion. The analogous reaction of alkenes and alkynes with difluoroiodotoluene in the presence of diphenyl diselenides affords the respective products of phenylselenofluorination in good yields [41],... 

Interestingly (example eight in Table 6.1), fluorination of alkenes with fluorine (F2) also requires special conditions. This is because fluorine (F2) attacks other bonds too and vide infra) will even attack saturated carbon to replace (substitute for) hydrogen. ... 

Fluorination of Alkenes by Addition Reactions. /S-Ruoro thioethers can be prepared by the addition of sulfenyl chlorides to alkenes in the presence of AgF. The addition to alkyl-substituted terminal alkenes usually produces anti-Markovnikov adducts with a primary fluorine. Unlike the corresponding chlorides, these materials do not undergo rearrangement to the thermodynamically more stable Markovnikov products (eq 5). ... 

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