Perfluoroalkyl iodides, oxidation

Perfluoroalkyl iodides are converted with ethylene to perfluoroalkylethyl iodides, which can be oxidized more readily than the parent perfluoroalkyl iodides. Oxidation with chromic acid yields a perfluoroalkanoic acid and a fluorinated alkanoic acid with an a-methylene group [93,117] ... 

Under similar conditions, perfluoroalkyl iodides react with alkyl phosphates to give fluorinated phosphine oxides, phosphinates, and phosphines [54 (equation 49) The product formed depends upon the stoichiometry and type of iodide used. When sodium alkyl trithiocarbonates are used as substrates, perfluoroalkyl tri-thiocarbonates ate formed [55]. 

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

Perfluoroalkyl iodides RfI and polyfluoroalkyl iodides of the type of RfCH2CH2I are directly oxidizable. Their oxidation potentials are summarized in Table 3 [35],... 

Chlorine trifluoride is one of the most powerful fluorinating agents particularly useful for the oxidation of perfluoroalkyl iodides to the corresponding perfluoroalkyliodine(III) difluorides and perfluoroalkyliodine(V) tetrafluorides.113,17 The reactions are conducted at — 78 to 20 °C in perfluorohexane or without solvent. Depending on the stoichiometric amount of chlorine trifluoride, the products are RfIF2 or RfIF4. 

Our early work examined the reaction of PCTFE with sulfur, selenium and phosphorous nucleophiles 9 to achieve high levels of functionalization through a well-precedented (in the case of perfluoroalkyl iodides)20"24 one electron transfer, radical anion chain process. While such a reaction demonstrated the feasibility of using one-electron processes for the functionalization of PCTFE, the carbon-sulfur linkage remained susceptable to oxidation. 

Perfluoroalkyl)methyl-substituted electrophilic cyclopropanes are synthesized in excellent yields by a chromium (III) chloride/iron powder-promoted reaction of perfluoroalkyl iodides with allylamalonic ester and its analogues (equation 51)67. Oxidative coupling of... 

The benzene derivatives containing the fluorinated sulfone have been prepared either by nucleophilic substitution of the 4-fluorophenyl derivative (e.g. 1) or by starting with the appropriately substituted sodium thiophenoxide and reacting with perfluoroalkyl iodide follow by oxidation with either MCPBA or chromium oxide (12. li.) The biphenyl derivatives have been prepared by palladium catalyzed cross coupling chemistry of the 4-bromophenyl derivative (e.g. 2) with substituted phenyl boronic acid (yields 37-84%) (JLH, .). Compound 16 has been prepared by palladium catalyzed cross coupling of (4-bromophenyl)perfluorohexyl sulfone with vinyl anisole in 37 % yield (JJL). The vinyl sulfones, 7 and 9, have been prepared by condensation of CH3S02Rf (JJL) with the appropriate aldehyde (yields 70,and 73%) following a literature procedure (1 ). Yields were not optimized. 

Electrochemical oxidation of perfluoroalkanoic acids can lead to radical derived products, although the same problems apply to such oxidations as applied to the electrochemical reduction processes of perfluoroalkyl iodides. 

Good yields of certain rhodium(III) perfluoroalkyl derivatives have been obtained in oxidative addition reactions of perfluoroalkyl iodides (R I) with rhodium (I) trifluorophosphine complexes (method C). 

Other functional polyfluorinated compounds are available by addition of perhaloalkyl halides to enol derivatives, e.g. formation of 1 and 2 (see also Table 4). The adducts formed from enol acetates or enol ethers are not very stable and their hydrolysis to give a-perhaloalkyl aldehydes or ketones is often rapid. However, the enol derivatives can be transformed either to give ketals using alcohols or to give various products by oxidation and reduction reactions. The peculiar perfluoroalkyl iodide addition to enamines is spontaneous at room temperature, e.g. formation of 3. ... 

Perfluoroalkylation of aliphatic, aromatic, and heterocyclic thiols by perfluoroalkyl iodides in the presence of triethylamine appears to occur spontaneously in daylight at room temperature, and is complete in 10-15 minutes to 2-3 hours. Thiols with lownucleophilicity are an exception to this rule thiol oxidation accompanies the reaction. 

High-temperature oxidations with nitrogen dioxide or nitrogen dioxide and chlorine followed by treatment with water convert perfluoroalkyl hydrides and perfluoroalkyl iodides into perfluorocarboxylic acids. Perfluoroalkyl bromides and especially perfluoroalkyl chlorides do not react appreciably (equation 201) [455]. 

Reactions of Tetraethyl Pyrophosphite with Perfluoroalkyl Iodides and Subsequent Oxidation... 

The reaction of tetraethyl pyrophosphite with perfluoroalkyl iodides in the presence of di-tert-butyl peroxide in l,l,2-trichloro-l,2,2-trifluoroethane (1-113) was described for the first time in 1981 Thermal decomposition of di-tert-butyl peroxide leads to the abstraction of an iodine atom and gives the reactive perfluoroalkyl radical, which reacts with tetraethyl pyrophosphite to produce the perfluoroalkyl phosphonite. Subsequent oxidation with tert-butyl hydroperoxide provides the desiied perfluoroalkylphosphonates in 40-71% yields (Scheme 3.40). 2 a photochemical variant, which avoids heating the reaction mixture with a peroxide, was reported later. This milder method allows the preparation of functionalized perfluoroalkylphosphonates in good yields... 

The most convenient sources of perfluoroalkyl radicals are perfluoroalkyl halides, from which the corresponding radicals can be generated photochemically or electrochemically [13]. Although electrochemical activation can be achieved either by oxidation or by reduction, e. g. of perfluoroalkyl iodides, the most popular method of activation is reduction (Scheme 2.98). The reductive radical generation can also be initiated photochemically via auxiliary radical sources, such as silanes or stannanes. 

The perfluoroalkyl iodides are subsequently oxidized to the bis (trifluoroacetates) or to the difluoroiodides, which again are reacted with a suitable arene in an elec-... 

Synthesis of the perfluoroalkyl P-amino alcohol 5 (70) required for the preparation of the perfluoroalkyl ketone VI as shown in Scheme 2 is illustrative of the method used to prepare analogous compounds. Tm-butyloxycarbonyl-L-cyclohexylalaninal 4 was condensed with perfluoroethyl or perfluoropropyl lithium which was generated in situ by the addition of methyllithium-lithium bromide complex to the corresponding perfluoroalkyl iodide. The alcohol 5 was isolated as an epimeric mixture which was used in the preparation of peptide IV. Oxidation using the Dess-Martin periodinane reagent (9) yielded the fluoroketone VI. 

FITS reagents are synthesized in high yields from oxidation of perfluoroalkyl iodides by trifluoroperacetic acid [60% H202 + (CF3C0)20] or by elementary fluorine followed by treatment with benzene or fluorobenzene in the presence of triflic acid in 1,1,2-trichlorotrifluoroethane or CF3COOH at 0°C to room temperature148 (equation 133). 

Perfluoroalkyl iodides Rfl and polyfluoroalkyl iodides of RfCH2CH2l type can be directly oxidized (see the oxidation potential data summarized in Table 4). ... 

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