Perfluoroalkyl lithium

Similarly, perfluoroalkyl lithium reagents, generated from the reaction of... 

Perfluoroalkyl lithium reagents undergo reactions typical of their hydrocarbon analogs. For example, perfluoroalkyl lithium reagents generated in situ from perfluoroalkyl iodides and alkyl lithiums reacted readily with aldehydes and ketones to yield the corresponding secondary and tertiary carbinols, and with esters to give either ketones or tertiary carbinols [12]. No 1,4-addition product is observed when a,/ -unsaturated ketones and esters are employed. 

Perfluoroalkyl lithium reagents reacted with imines in the presence of boron trifluoride to give the corresponding adducts in good yields [15], and this methodology has been applied to the synthesis of perfluoroalkyl-containing amino acids [16] (Scheme 7). 

Perfluoroalkyl-lithium derivatives are thermally unstable and their use in organic synthesis has been limited by competing (3-elimination processes [29]. Pentafluoroethyl-lithium has a half-life of around 8 h at —78° C [30]. In complete contrast, perfluorinated bridgehead lithio derivatives are much more stable since, in these cases, elimination of LiF would contravene Bredt s rule and would, therefore, be a higher-energy process. Consequently, perfluoroadamantyl-lithium is stable at 0° C for several days [31] (Figure 6.22). 

Reactions which partly compensate for the unsuitability of the perfluoroalkyl-lithium route involve addition of fluoride ion to an unsaturated site giving corresponding carb-anions (Cs or K derivatives) that may be used in synthesis (see Chapter 7, Section IIC,... 

Higher homologues of perfluoroalkyl lithium compounds are usually generated at very low temperatures (—78 °C or below) in situ and directly reacted with a suitable electrophile, often a carbonyl compound, for example an aldehyde, ketone [45], or ester [46] (Scheme 2.117). If this carbonyl compound is chiral, reasonable diastereo-meric excesses can be obtained [47]. The corresponding trifluoromethyl lithium (CFjLi) is still unknown, because of its immediate a-elimination with difluorocar-... 

Scheme 2.117 Generation and in-situ reaction of perfluoroalkyl lithium species [47].

Perfluorobicyclo[2,2,2)oct-l-yl-lithium (1), the most stable perfluoroalkyl-lithium prepared so far, being unchanged after storage at 35 °C for 1 h in ether solution, can be obtained by metalation of Ifl-tridecafluorobicyclo-[2,2,2]octane (see p. 5) with methyl-lithium in ether at -50°C it reacts with deuterium oxide, methyl iodide, and iodine to yield I-deuterio-, 1-methyl-, and l-iodo-tridecafluorobicyclo[2,2,2]octane, respectively. ... 

The allyltin compounds (CH2 CH CH8)aSn-CaF7-n, (CHa CH-CHj)a-Sn-CaF, and (CHj CH-CHa)aSn(C2F,)j have been synthesized from allyltin bromides and the appropriate perfluoroalkyl-lithium, prepared from the corresponding iodide and methyl-lithium arguments based on comparisons between u.v. and i.r. spectral data for these compounds and those for their alkyl counterparts have been advanced in support of hyperconjugation in allyltin derivatives ... 

Polyfunctional fluoronitro alcohois are provided by tlie SRNl reaction of a perfluoroalkyl iodide or alkylene diiodides with the anhydrous lithium salt of 2-nitropropane l,3-diol acetonide. Hydrolysis of the resulting perfluoroalkyl-... 

Lithium chlorodifluoroacetate in preparation of perfluoroolefins from perfluoroalkyl ketones, 48, 119... 

The procedure illustrates a fairly general method for the preparation of -substituted perfiuoroolefins. The method has been applied to the synthesis of 2-cyclohexyl- (70%), 2-benzyl- (61%), and 2-(/>-fluorophenyl)perfluoropropenes (67%), and it is probably applicable to any a-trifluoromethyl ketone. Olefins containing a perfluoroalkyl group other than trifluoromethyl can be prepared by the same procedure by the substitution of lithium chlorodifluoroacetate for sodium chlorodifluoroacetate.7 Other routes to / -substituted perfiuoroolefins are not general or convenient. Routes to perfiuoroolefins generally yield the a-substi-tuted olefin rather than the /3-substituted olefin. 

Silyl enol ethers have also been used as a trap for electrophilic radicals derived from a-haloesters [36] or perfluoroalkyl iodides [32]. They afford the a-alkylated ketones after acidic treatment of the intermediate silyl enol ethers (Scheme 19, Eq. 19a). Similarly, silyl ketene acetals are converted into o -pcriluoroalkyl esters upon treatment with per fluoro alkyl iodides [32, 47]. The Et3B/02-mediated diastereoselective trifluoromethylation [48,49] (Eq. 19b) and (ethoxycarbonyl)difluoromethylation [50,51] of lithium eno-lates derived from N-acyloxazolidinones have also been achieved. More recently, Mikami [52] succeeded in the trifluoromethylation of ketone enolates... 

Scheme 19 Perfluoroalkylation of silyl end ethers and lithium enolates via iodine atom transfer...

In contrast to the difficulty encountered in the direct reaction of perfluoroalkyl iodides with lithium metal [17-19], perfluoroalkyl magnesium reagents can be... 

The pale yellow crystalline trifluoroacetyl triphenylsilane and a number of other per-fluoroalkyl acyl triphenylsilanes have been prepared by simple acylation of triphenylsilyl lithium with perfluoroalkyl anhydrides122. 

Perfluoroalkyl ketones have been reduced in high ee using a simple alkoxide lithium (S)-l-phenylethoxide, for example, reduces 2,2,2-trifluoroacetophenone to its (5>carbinol in 80% ee and 61% yield at 0°C, with acetophenone produced as by- ... 

Reduction of perfluoroalkyl ketones with chiral lithium alkoxides gave chiral a-perfluoroalkyl alcohols in high enantiomeric excesses. The order of steric effects on this reaction is estimated as C7F15 > substituted phenyl > CF3.388... 

Lastly, electron transfer processes can also compete with nucleophilic acyl substitution in the reaction of perfluorodiacyl peroxides with Grignards [305]. Such a process can lead to a coupling of the Grignard with the perfluoroalkyl radical intermediate. (In contrast, benzyl lithium gives no perfluoroalkylation under the same conditions.)... 

Attempts to prepare a (/ -fiuorovinyl)iodonium salt from l-decynyl(phenyl)iodonium tetrafluoroborate by the procedures employed for / -chloro- and (/ -bromovinyl)iodonium halides have been unsuccessful103. Admixture of the decynyliodonium salt and lithium fluoride in acetic acid ultimately (2 days, rt) leads to l-acetoxy-2-decanone103. (Z )-(/ -Fluoro-jS-perfluoroalkylvinyl)iodonium triflates, on the other hand, can be made by the treatment of (1H, li/-perfluoroalkyl)phenyliodonium triflates with sodium hydride (equation 178)136. Apart from 2-fluoro-l-hexadecenyl(phenyl)iodonium chloride (synthesis not described)104, these are the only reported examples of (/ -fluorovinyl)iodonium salts. 

Perfluoropropynyl [15, 26, 27] and perfluorovinyl [16, 28-30]-lithium and -magnesium are considerably more stable than perfluoroalkyl derivatives, whilst the corresponding perfluoroaryl derivatives may be used as effectively as in the hydrocarbon series, and direct syntheses involving iodo compounds are also possible (Figure 10.3). 

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