Butyl anions

NMR spectroscopy is ideal for detecting charged fluorinated intermediates and has been applied to the study of increasingly stable carbocation and carbanion species. Olah [164, 165] has generated stable fluorocarbocations m SbFj/SOjClF at low temperatures The relatively long-lived perfluoro-rerr-butyl anion has been prepared as both the cesium and tris(dimethylamino)sulfonium (TAS) salts by several groups [166, 167, 168], Chemical shifts of fluonnated carbocations and carbanions are listed m Table 23. 

Pcrfluoro-f-butyl Anion in the Synthesis of Organofluorine Compounds ... 

In order to illustrate this point, we report the opposite behavior of the ally and n -butyl anions in the substitution of an optically active fluorosilane, 1-NpPhMeSi—F. The first leads to inversion (91% IN) and the latter to retention (98% RN) (49), when the reactions with allyl- and n -butyllithium are carried out in the presence of a cryptand specific for lithium cation. The use of a cryptand makes it possible to study the difference in behavior of the anion species alone, since it avoids the possibility of electrophilic assistance by Li+ which could affect the apicophilicity of the fluorine atom. 

The base attacks the methyl hydrogens because they are less hindered—they are attached to a primary carbon atom, well away from the other axial hydrogens. E2 eliminations with hindered bases typically give the less substituted double bond, because the fastest E2 reaction involves deprotonation at the least substituted site. The hydrogens attached to a less substituted carbon atom are also more acidic. Think of the conjugate bases a t-butyl anion is more base... 

A suitable initiator for this process is butyl lithium, (CH3CH2CH2CH2) Li. The butyl anion (abbreviated Bu ) reacts with the end carbon atom in a molecule of acrylonitrile to give a new anion ... 

In contrast, for />-fluoro carbanions, negative hyperconjugation [35] has a stabilizing effect. For example, in the perfluoro-tert-butyl anion the negative charge is not centered completely at the carbon atom, but comparably high partial charges are located on all the j5-fluorine atoms [33] (Scheme 2.110). 

The stereochemistry observed in proton exchange reactions of carbanions is dependent on the conditions under which the anion is formed and trapped by proton transfer. The dependence on solvent, counterion, and base is the result of the importance of ion pairing effects. The base-catalyzed cleavage of 1 is illustrative. The anion of 1 is cleaved at elevated temperatures to 2-butanone and 2-phenyl-2-butyl anion, which under the conditions of the reaction is protonated by the solvent. Use of resolved... 

Methyl anion Ethyl anion sec-Propyl anion tert-Butyl anion... 

In this view, the lower ionization potential of the terf-butyl anion in comparison with that of the n-butyl anion is ascribed to the greater stability of the tert-butyl radical (8). 

Formation of alcohols, which is often an important side reaction during the photolysis of esters and especially benzoates in HMPA, might be the result of photohydrolysis. For the reduction of esters by metals, alcohol formation is due to the presence in the reaction mixture of metal amides. " Thus, in the presence of r-butanol as a hindered alcohol, these metal amides are neutralized and the proportion of alcohol formed decreases. Reaction of r-butylate anions is slow enough to be neglected under these reaction conditions. However, the strong basic conditions in the reduction by metals make this reaction less attractive than the photoreduction process for applications in the multistep syntheses of polyfunctional molecules. 

Treatment of perfluoro-t-butylmercuric chloride with perfluoropropene in the presence of potassium fluoride (in DMF at 50 °Q yields bis(perfluoro-isopropyl)mercury via displacement of perfluoro-t-butyl anion. Potassium fluoride-initiated reaction of the mercurials (RF)jHg [Rf = (CFgljCF or (CFg)3C] with sulphur in hot DMF gives the corresponding mercaptides [(RFS)aHg]. Displacement of Rf from these mercurials with sodium iodide in a dipolar aprotic solvent occurs readily and, in the absence of electrophilic traps, perfluoro-olefin formation (CFg-CXiCFg X = F or CF3) occurs via j3-elimination of fluoride ion. ... 

For the ferf-butyl anion 3, because the three CH3 are electron-donating groups (+1), this makes 3 less stable than the methyl anion 2. 

The final part of this chapter will focus on the recent chemistry which has been reported involving potassium magnesiate chemistry. The first examples to be discussed involve the characterization of solvent-free potassium magnesiates which contain two TMP and one n-butyl anions per potassium (or magnesium) cation [ie, KMg(TMP)2 Bu ]. Three different oHgomeric forms have been reported including the polymeric [KMg(TMP)2 Bu]oo 62, the tetrameric [KMg(TMP)2 Bu]4 63, and the hexameric [KMg (TMP)2 Bu]6 64 examples (Fig. 41). The structures of 63 and 64 are architecturally similar to the inverse crowns discussed in Section 3.3 but they stiU retain the basic -butyl arm, and as such they have been coined as pre-inverse... 

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