Alcohols fluoroolefins

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). 

Strategies centered on reductive introduction of the fluoroolefin via a geminal difluoro allylic array have been reviewed [66]. In an introductory example to this synthetic approach, Okada et al. [67] developed a completely stereoselective synthesis of Z)-2,5-syn 2-alkyl-4-fluoro-5-hydroxy-3-alkenoic acids through the Cu(l)-mediated allylic substitution reaction of trialkylaluminum with the (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative (61) (Scheme 21). Reaction... 

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). 

An alternate route to fluoroolefins relies upon the ease of reduction of difluoroolefins(18). Reduction of 114 with sodium bis(2-methoxyethoxy)aluminum hydride (Scheme 35) afforded the fluoroolefins 115 and 116 considerably enriched with the (E)-isomer 116. In a complementary reaction, reduction of the allylic alcohol 117 with LiAlH4 afforded selectively the (Z)-isomer 118. The difluoromethacrylic acid (121) was prepared in similar manner from 120 (Scheme 36) (53 for related examples see references 75 and 76). Under more forcing conditions, further reduction afforded 3-fluoromethacrylic acid 122. Of more general use is the reaction of 120 with Grignard reagents whereupon the 1,4-addition elimination mechanism offers an entry into a-difluoromethylene substituted aliphatic and aromatic carboxylic acids 123. Ester enolates (125) have been shown to add to trifluoropropene (124) forming the difluoroolefins (126) (Scheme 37) (54). 

Since the conversion of fluorinated olefins to vinyl ethers is knownl, it should be emphasized that the principal benefit from the silyl ether chemistry is increased selectivity and yield. Base-catalyzed reaction of alcohols and fluoroolefins almost always gives a mixture of substitution and addition products, but clean substitution occurs with silyl ethers. Homogeneity, which persists during bulk polymerization, is an additional attractive feature. Substitution of the first fluorine in a 1, 2-disubstituted perfluorinated olefin proceeds more rapidly than subsequent fluorine substitution in the product vinyl ether. The 2/1 adducts shown in Scheme 4 are therefore conveniently prepared in excellent yield. On a laboratory scale, these difunctional vinyl ethers permit good control of stoichiometry required for polymer formation. 

Many synthetic polymers are treated with H2O2 to reduce colour or odour and, sometimes, to increase long-term stability. Among these can be mentioned poly(fluoroolefins) [290], polyvinyl alcohol [291], polyethylene [292] and polybutadiene [293]. Optical lens resins can be made more transparent by using persalts [294]. 

However, they are too slow to react with 9-BBN. Catecholborane and pinacolborane react with fluoroolefins in the presence of a transition metal catalyst. However, reactive boranes, such as dichloroborane-methyl sulpfide readily react with mono, and disubstituted terminal perfluoroaUcenes in the presence of BCI3. The latter coordinates to Me2S and releases the free dichloro-borane, which instantaneously hydroborates theperfluoroalkenes. Oxidation under alkaline conditions furnishes the primary alcohol in >98% regioselectivity (eq 8). Alternatively, the free dichloroborane prepared via Matteson s protocol can also be used for the hydroboration of fluoroolefins. 

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