Reaction with fluoroalkyl

A second method is based on the abnormal course of the Koenigs-Knorr reaction with fluoroalkyl alcohols. Indeed, when there are two or three methylenes between the Rf group and the hydroxyl, the reaction does not lead to substitution of the anomeric bromide but instead affords an orthoester. In the presence of mercuric bromide, this orthoester can undergo a rearrangement into an (9-fluoroalkyl glycoside (Figure 6.47). 

Perfluoroalkylation of substituted benzenes and heterocyclic substrates has been accomplished through thermolysis of perfluoroalkyl iodides in the presence of the appropriate aromatic compound Isomeric mixtures are often obtained W-Methylpyrrole [143] and furan [148] yield only the a-substituted products (equation 128) Imidazoles are perfluoroalkylated under LTV irradiation [149] (equation 129). 4-Perfluoroalkylimidazoles are obtained regioselectively by SET reactions of an imidazole anion with fluoroalkyl iodides or bromides under mild conditions [150] (equation 130) (for the SET mechanism, see equation 57)... 

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)... 

Fluoroalkyl ketones may be used as the electrophilic partners in condensation reactions with other carbonyl compounds The highly electrophilic hexafluo-roacetone has been used in selective hexafluoroisopropyhdenation reactions with enol silyl ethers and dienolsilyl ethers [f] (equation 1)... 

The enhanced reactivity of fluoroalkyl ketones is also manifested in the failure to stop the reaction with hydrogen cyanide at the stage of cyanohydrins Instead, oxazohdinones or dioxolanones are formed (equation 11) If, however, the reaction IS conducted under basic conditions with sodium bisulfite and sodium cyanide, the desired cyanohydrin can be prepared [ll ... 

Fluoroalkyl ketone enolates and enol etliers have also been use in condensation reactions with ketones [22] Interestingly, these materials fail to undergo Dar/ens-type side reactions (equation 18)... 

Unlike the 3-position, the 5-position is very susceptible to nucleophilic substitutions and additions. Thus, a series of publications report that 5-fluoroalkyl-l,2,4-oxadiazoles 94 undergo reaction with hydrazine or hydroxylamine to furnish 3-fluoroalkyl-l,2,4-triazoles 95 (X = NH) and 3-fluoroalkyl-1,2,4-oxadiazoles 95 (X = 0), a reaction that proceeds via addition of the nitrogen nucleophile to the 5-position (Scheme 9) <2005JOC3288, 2004EJ0974, 2003JOC605>. 

S. Hadida, M. S. Super, E. J. Beckman, D. P. Curran, Radical Reactions with Alkyl and Fluoroalkyl (Fluorous) Tin Hybride Reagents in Supercritical C02 , J. Am. Chem. Soc 1997,119,7406. 

Sulfur also reacts with fluoroalkyl mercurials and fluoroalkyl iodides to give fluorothioacyl halides. In the case of the reaction with mercurials, the halide formed is determined by substitution on the carbon attached to mercury. For example, bis(perfluoroethyl)mercury gives trifluorothioacetyl fluoride and bis-(l,l-dichloro-2,2,2-trifluoroethyl)mereury gives trifluorothioacetyl chloride. 

Reaction of elemental sulfur with fluoroalkyl iodides has not received very much attention, but it has been shown that sulfur converts 4,4-diiodoperfluoro-l-butene to pentafluoro-3-butenoyl fluoride. 

Af,Ar,AOV -Tetramethylnaphthalene-l,8-diamine described as Proton Sponge 38 (see Section 1.2) has the ability to act as a fluoride ion donor when its hydrofluoridc is used. Furthermore, it may be used to promote oligomerization reactions of fluorinated alkenes, e.g. 3, and poly-fluoroalkylation reactions with activated perfluoroaromatic compounds, e.g. 4.38... 

Table 3. Reactions of Bromine Trifluoride with Fluoroalkyl Bromides108...

Selectivity and reactivity of mixed anhydrides toward primary and secondary aliphatic and aromatic amines has been studied in details [42, 43] (equation 22) Fluorocarboxyhc acids and their derivatives are used as building blocks in condensa non reactions with dinucleophdic species for the synthesis of fluoroalkyl-subsntuted heteroaromahe systems [8 9,40,44,45, 46, 47 48] (equanons 20 21, and 23)... 

Fluoromethyl ketones are one of the most widely used classes of peptidyl a-fluoroalkyl ketones, second only to trifluoromethyl ketones. Peptidyl fluoromethyl ketones are very effective as irreversible inhibitors of cysteine proteases the first reported use of a fluoromethyl ketone compound was the use of Z-Phe-Ala-CH2F as an irreversible inhibitor of cathepsin BJ2,31 Today, many lysine and arginine derivatives have been synthesized as potential inhibitors for trypsin and trypsin-like enzymesJ3 There are four basic methods for the synthesis of peptide fluoromethyl ketones (1) the reaction of HF with peptide diazomethyl ketones (Section 15.1.4.1.1), (2) a halogen-exchange reaction with a chloro-, bromo-, or iodomethyl ketone (Section 15.1.4.1.2), (3) a Henry nitro-aldol condensation reaction (Section 15.1.4.1.3), and (4) a modified Dakin-West acylation reaction (Section 15.1.4.1.4). 

The reactions of ethylenes substituted with fluorine and chlorine were determined by Anicich, Bowers and coworkers211-216. Su and collaborators217 tested several reactions of fluoroalkyl radical anions with C2F4 ... 

---