Alkyl fluorides, activation

Fluoride-activated monoorganotin derivatives can be used in cross-coupling with aryl or vinyl iodides to transfer a very wide range of organic residues, including alkyls which are not normally reactive (Equation (12)) 62... 

The alkylation reaction is initiated by the activation of the alkene. With liquid acids, the alkene forms the corresponding ester. This reaction follows Markovnikov s rule, so that the acid is added to the most highly substituted carbon atom. With H2S04, mono- and di-alkyl sulfates are produced, and with HF alkyl fluorides are produced. Triflic acid (CF3S020H) behaves in the same way and forms alkyl triflates (24). These esters are stable at low temperatures and low acid/hydrocarbon ratios. With a large excess of acid, the esters may also be stabilized in the form of free carbenium ions and anions (Reaction (1)). 

Similarly to alkyl fluorides, fluorocyclohexane is resistant toward catalytic hydrogenolysis. Hydrides and metals appear to be more efficient in the hydrodefluorination of alicyclic fluorine-containing compounds. Butyllithium in refluxing hexane defluorinates fluorocyclohexane to cyclohexane.20 The complete defluorination of fluorocyclohexane (11) is accomplished by activated magnesium in propan-2-ol, but the reaction leads to the predominant formation of cyclohexene.21... 

The fluoFoalkylamine reagent (FAR) 2-chloro-l,l,2-trifluorotriethylamine gives alkyl fluorides from alcohols in one step and is known as the Yarovenko reagent." This reagent is less reactive than DAST but was used intensively before the introduction of DAST. Rearrangement and elimination are similar with FAR and DAST (equations 39 and 40)." " This may be explained by the similar mechanism. Activation of the alcohol by intermediate formation of ester-type derivatives is followed by 5N2-type displacement by fluoride ion (Scheme 32). 

Alkyl fluorides are relatively stable and have been rarely used as alkylation agents in alkylation chemistry compared with other alkyl halides. Maruoka et al., however, found that MesAl efficiently catalyzes the alkylation of KSA with tertiary alkyl fluorides (Scheme 10.94) [255]. Under the same conditions alkylation with the corresponding chloride does not proceed. The strong activation of tertiary alkyl fluorides by McjAl originates from fhe exceedingly high affinity of aluminum for the fluorine atom (Section 10.2.1.1). 

This phenomenon is rather specific. That is, a Cr/silica catalyst is preferred, not a Cr/silica-titania or a Cr/silica-alumina. It must be activated at a high temperature or treated with fluoride, perhaps to reduce potential ligands. Then it must be reduced in CO. When contacted with some cocatalysts, especially aluminum alkyls, the catalyst then becomes highly sensitive to H2. As illustrated in Table 60, in this series of experiments there was a huge jump in MI only when all of these treatments were combined. Activation at 600 °C does not work unless the catalyst also contains fluoride. Activation at 800 °C is effective without fluoride, but the effect is more pronounced with fluoride. The data shown in Figure 214 illustrate the huge shift in the MW distribution resulting from this combination of catalyst and reaction variables. 

Optically active secondary alkyl halides. Landini et al have extended their study of the conversion of methanesulfonates to alkyl fluorides to the reaction of the methanesulfonate (1) of (-)-(R)-2-octanol with KF, KCl, KBr, or KI in the presence of a phase-transfer catalyst in a two-phase system. In the case of... 

Ytterbium triiodide activates the C-F bond of alkyl fluorides giving iodides in high yields (82-98%) in CH2CI2 or CHCls. The reaction is successful in the presence of ketone, ether, alcohol, ester, trialkylamine, aryl, and cyano groups in the substrate and with primary, secondary, and tertiary fluorides but does not occur with polyfluorinated compounds, or those with a CF2, CF3, or group. The reaction... 

After nearly 70 years, in 1972 Reuben Rieke showed that even Idnetically inert alkyl fluorides reacts with activated magnesium - the latter is prepared by in situ... 

VinyUdene fluoride can be polymerized in saturated fluorinated or fluorochlorinated solvents. These solvents dissolve fluoroalkenes like vinylidene fluoride and organic peroxide catalysts. Polymerization thus takes place in a homogeneous phase and the resulting poly-vinylidene fluoride is insoluble in the solvent, making the product readily separable from the solvent. In addition to organic peroxides, the reaction can be initiated or induced by radiation. This is helpful in avoiding contamination of the product with other reaction components such as the initiator, surfactant, and the others. Alkyl boron activated by oxygen has also been reported to catalyze vinylidene fluoride and vinyl fluoride polymerization in water and solvents. ... 

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