Halides perfluoroalkyl iodides

Particularly alkyl halides which have a perfluoroalkyl group at the /3-position undergo smooth carbonylation. Probably the coordination of fluorine to form a five-membered chelate ring accelerates the reaction. Double carbonylation to give the a-keto amide 915 is possible in Et NH with the fluorine-bearing alkyl iodide 914[769,770]. The ester 917 is obtained by the carbonylation of the /3-perfluoroalkyl iodide 916 in ethanol. 

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

Solvent plays a significant role in these reactions In contrast to the formation of organocadmium compounds in the duect reaction of perfluoroalkyl iodides and cadmium powder in DMF [729], dimerization of the perfluoroalkyl halide was observed in acetonitrile [777] (equation 100)... 

Perfluoroalkylation can be accomplished via direct reaction of peifluoroalkyl halides and copper with aromatic substrates [232, 233, 234, 235, 236] Thus, perfluoroalkyl iodides or bromides react with functionalized benzenes m DMSO m the presence of copper bronze to give the corresponding perfluoroalkylated products directly in moderate to good yields [233] (equation 157) Mixtures of ortho, meta, and para isomers are obtained [232, 233], The use of acetic anhydride as solvent gives similar results [234, 235], Similarly, the direct reaction of perfluoroalkyl iodides and pyrroles with copper metal regiospecifically gives the 2-perfluoroalkylpyrroles [236] (equation 158). 

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)... 

Direct electrochemical reduction of perfluoroalkyl halides generates perfluoroalkyl radicals or anions depending on the electrolytic conditions and starting halides. Calas et al. have performed the electrocatalytic addition of perfluoroalkyl iodides to 3-hydroxyalkynes in aqueous KCI emulsion using a... 

Despite the lower reactivity of solvated perfluoroalkylzinc reagents, perfluoroalkyl iodides undergo synthetically useful zinc-mediated reactions under Barbier conditions which often employ ultrasound and co-catalysts. Under these conditions, the zinc reagents are not well characterized and radical intermediates and SET mechanisms are proposed in some cases. Representative examples are presented below and include the ultrasound-promoted, zinc-mediated perfluoroalkylation of various substrates as reported by Ishikawa and coworkers (Scheme 10)123 126. Yields of carbinols could be improved by use of Ti(II) co-catalyst. Ultrasound promoted the coupling of perfluoroalkyl iodides with vinyl and allyl halides in the presence of Pd co-catalysts. 

Perfluoroalkyl iodides reacted with trialkylsilyl chloride in DMF in the presence of zinc followed by hydrolysis with acid to give perfluoroaldehydes in good yields [55]. Recently, Hu reported a new preparation of perfluoroalkyl aldehydes via reaction of perfluoroalkyl halides and DMF, initiated by redox... 

Alkyl halides with (3-hydrogens generally undergo only elimination reactions under the conditions of the vinyl substitution (100 C in the presence of an amine or other base). Exceptions are known only in cases where intramolecular reactions are favorable. Even alkyl halides without (3-hydrogens appear not to participate in the intermolecular alkene substitution since no examples have been reported, with the exception of reactions with benzyl chloride and perfluoroalkyl iodides. 

A solution of perfluoroalkyl iodide (0.4 mmol), a-chlorostyrene (1.2 mmol) and Bu3SnSnBu3 (0.44 mmol) in benzene (3 ml) was irradiated using a metal halide lamp (National Sky-beam MT-70) in Pyrex tube under 02 atmosphere for 5 h. After removal of the solvent, ethanol and hydrazine acetate were added. The resultant solution was stirred under refluxing conditions for 2 h. After removal of the solvent, the residue was chromatographed on silica gel using a mixture of hexane and dichloromethane as an eluent, to give perfluoroalkylated pyrazole in 59% yield [117]. 

Among the halides that react through this process are unactivated aromatic and heteroaromatic halides, vinyl halides, activated alkyl halides [nitroalkyl, nitroallyl, nitro-benzyl and other benzylic halides substituted with electron-withdrawing groups (EWG) as well as the heterocyclic analogues of these benzylic systems] and non-activated alkyl halides that have proved to be unreactive or poorly reactive towards polar mechanisms (bicycloalkyl, neopentyl and cycloalkyl halides and perfluoroalkyl iodides). 

The reaction of perfluoroalkylcopper compounds, prepared in situ from the perfluoroalkyl iodide and copper, with ip -hybridized organic halides [Eq. (73)] in refluxing pyridine utilizes the thermal stability of the intermediate copper compounds and their failure to react with sp -hybridized halides (29, 30). 

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. ... 

The processes described above invoke breakdown of intermediate radical-anions to give perfluoroalkyl radicals and halide ion this is supported by theory [23] and ESR studies [24]. However, t-perfluoroalkyl iodides do not react with nucleophiles in this manner because it is thermod3mamically more favourable for these particular intermediate radical-anions to break down into relatively stable perfluorocarbanions and iodine atoms [23] (Figure 5.8). The reaction of tertiary perfluoroalkyl iodides and hexene to give perfluoroalkenes supports this conclusion [25]. 

Alkyl iodides " and perfluoroalkyl iodides react with Zn-Cu couples. Use also is made of mixtures of the alkyl iodide and bromide (e.g., a 1 3 ratio of n-BuI n-BuBr gives n-BujZn in high yield). Byproducts, such as alkenes (R—H) and alkanes, RH, can become problems for secondary alkyl halides, RX, and for these care and control of the conditions and workup are vital. Success is possible as shown by yields of 85% for i-PrjZn, and 72% for s-Bu Zn. Tertiary alkyl iodides do not produce organozincs. 

Furtliermore, we could show that the reaction is not limited to perfluoroalkyl iodides. When methyl or ethyl halides were passed through a mixture of red phosphorus and copper at around 350 °C mainly phosphorus dihalides were produced. The phosphinous halide is formed in small amount along with some phosphines. With methyl bromide, e.g., the reaction product is composed of 80-90% CH3PBr2, 2-3% (Cf j-PBr and 7-14% (CH3)2PBr3. 

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. 

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