Allylic fluorines

The 1,3-dipolar cycloadditions offluonnatedallenes provide a rich and varied chemistry Allenes, such as 1,1-difluoroallene and fluoroallene, that have fluorine substitution on only one of their two cumulated double bonds are very reactive toward 1,3-dipoles Such activation derives from the electron attracting inductive and hyperconjugative effects of the allylic fluorine substituent(s) that give nse to a considerable lowering of the energy of the LUMO of the C(2)-C(3) n bond [27]... 

Interestingly, the photolysis of methyl 3-azido-2.6-difluorobenzoate (61) in diethylamine yields, in addition to the two expected 3//-azepines 62 and 63, a third azepine 64 formed by nucleophilic displacement of allylic fluorine from the 3-position by diethylamine.188 Displacement of allylic halogen from haloazepines has been noted previously.177... 

In 1948 Hcnne and Newby reported their unsuccessful attempt to prepare hexafluoropropene by allylic fluorination of3-chloropentafluoropropene (1). Instead they obtained the rearranged product 2 as an EiZ mixture in good yield.6... 

Finally, intense ultraviolet irradiation of perfluoro(2.3-dimethylbut-2-ene) (14) yields terminal alkene 15 quantitatively.35 Unfortunately, photolysis of more complex perfluoroalkenes gives mixtures of products resulting from migration of both allylic fluorine and allylic per-fluoroalkyl groups. Perfluorobut-2-ene only undergoes geometric isomerization. Pyrolysis of 14 at temperatures up to 300 C in the dark does not lead to detectable rearrangement. 

In perfluorinated trialkylethenes the single vinylically bonded fluorine is hydrogenolyzed with hydrogen over palladium though only partially, but with complete regioselectivity.35 In contrast, in perfluorinated tetraalkylethenes allylic fluorine is eliminated while the hydrogen atom attacks the double-bonded carbon.36... 

Cyclic alkenes with alkali alkoxides give almost exclusively products of nucleophilic substitution of one or more vinylic or allylic fluorine or halogen atoms. The preference of the attack is expressed by the sequence fluorine > chlorine > bromine.68... 

The mechanism includes formation of F-allyl carbocation 1 as a result of abstraction of activated allylic fluorine from HFP by a Lewis acid and addition 1 to TFE followed by isomerization of terminal olefin into product 11 ... 

Hydrolysis of perfluoro-3-isopropyl-4-methylpentenyl-2-sulfenyl chloride 34 having a mobile allyl fluorine atom ends with the formation of perfluoro-2,4,4-trimethyl-3-isopropylthiete 35 (yield 30%) (89IZV1380). The reaction occurs via the intermediate formation of the derivative of sulfenic acid 36 due to the high mobility of the allylic fluorine atom. 

Allylic fluorines in the starting compounds are reactive enough to be displaced, in an SN2 reaction, by the methoxide anion. The allylic fluorine at the other end of the double bond is displaced by the oxygen of the... 

The reaction starts probably by elimination of the tertiary fluorine atoms. Thus, a bicyclic olefin is formed. Its double bond activates the four allylic fluorines for nucleophilic displacement by thiophenoxide anions to give l,4,5,8-tetrakis(phenylthio)perfluoro-A9 10-octalin. 

The CO2 fixation into (perfluoroalkyl)iodoalkanes, (perfluoroalkyl)-iodoalkenes and (perfluoroalkyl)alkenes, catalyzed by electrogenerated nickel complexes, afforded perfluoroalkyl carboxylic acid derivatives. The electrocarboxylation of perfluoroalkyl olefins proceeded with double bond migration and loss of an allylic fluorine atom. 

The addition of catalytic amount of a Lewis acid, such as BF3, completely changes the course of the reaction of hexafluoropropene and sulfur trioxide. Allyl fluorosulfate 30 (rather than sultone 23) is the major product of the reaction in this case. The proposed mechanism of this reaction involves the formation of fluor-osulfated boron fluoride intermediate by abstracting an allylic fluorine from hexafluoropropene to form the perfluoroallyl cation, which is further stabilized by addition of -OSO2F group affording 30 (Scheme 2.15). It should be pointed out, however, that the concerted mechanism of SO3 insertion into allylic C-F bond of CF3 group also cannot be ruled out. 

A number of interesting reactions of the dimer (66) with nucleophiles have been described. Addition of sodium methoxide in methanol yields dimethoxy-ether (71), by replacement of the olefinic fluorine atom and of an allylic fluorine, which in turn yields keten (72) by reaction with sulphur trioxide at 30—40 Diverse... 

A highly regioselective, Pd-catalysed allylic fluorination of phosphoro-thioate esters (72) has been reported by Lauer and Wu. The mildness of the reaction conditions have been demonstrated by its functional group tolerance (Scheme 23). ... 

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