Triphenylmethyl anion

Diphenylmethyl and triphenylmethyl anions are still more stable and can be kept in solution indefinitely if water is rigidly excluded. Condensed... 

Carbanions can, under suitable conditions, be oxidised thus the triphenylmethyl anion (85) is oxidised, fairly slowly, by air ... 

A comparison of displacements on (/ )-2-octyl tosylate, chloride and bromide by PhsCLi, Ph3SiLi, PJ GeLi and Pt SnLi is summarized in Table 640. In each case, the Sjv2 product is formed with inversion. The basicity of the triphenylmethyl anion caused... 

Electrogenerated bases (see Chap. 14) can be prepared in situ and tailored for regioselective deprotonation. Regioselective alkylation of an unsymmetrical cyclic ketone was achieved by using an electrogenerated triphenylmethyl anion (Eq. 5, RX = CH3I,... 

To obtain complete conversion of ketones to enolates, it is necessary to use aprotic solvents so that solvent deprotonation does not compete with enolate formation. Stronger bases, such as amide anion ( NH2), the conjugate base of DMSO (sometimes referred to as the dimsyl anion),2 and triphenylmethyl anion, are capable of effecting essentially complete conversion of a ketone to its enolate. Lithium diisopropylamide (LDA), which is generated by addition of w-butyllithium to diisopropylamine, is widely used as a strong... 

TITTe have reported that the triphenylmethide ion in dimethyl sulfoxide (DMSO) solution reacts with oxygen at a rate approaching the diffusion-controlled limit (k > 109 liters/mole sec.) (16). The triphenylmethide ion is actually more reactive toward molecular oxygen than the triphenylmethyl radical. Because of the reactivity of the triphenylmethyl anion toward molecular oxygen, it is possible to measure the rate of ionization of triphenylmethane in basic solution by the rate of oxygenation. 

The photostimulated reaction of PhX (X = Cl,Br,I) with triphenylmethyl anion (117) in THF leads to phenylated products 118 and 119, although in low yield, together with phenylation of the THF solvent (equation 82)163. 

Electron transfer has been invoked in the photochemistry of tetraphenylcyclo-pentadienide anion 11 in DMSO, which gave the dimethylated product 12, in addition to dimeric coupling products [32], The mechanism of reaction is similar to that shown in Scheme 1 for photolysis of triphenylmethyl anion in DMSO, in... 

Both the results and the reasoning, however, were rigorously confirmed shortly thereafter. Eventually it became clear that Gomberg s synthetic failure led to the discovery of stable radicals, a new class of organic species, derivatives of trivalent carbon. Further studies led to the understanding that the triarylmethyl system is extremely versatile and gives rise to the preparation of other types of derivatives of trivalent carbon, e.g. salts of the triphenylmethyl cation 66b and the triphenylmethyl anion 66c. 

The triphenylmethyl carbanion, the trityl anion, can be generated by the reaction of triphenylmethane with the very powerful base, n-butyllithium. The reaction generates the blood-red lithium triphenylmethide and butane. The triphenylmethyl anion reacts much as a Grignard reagent does. In the present experiment it reacts with carbon dioxide to give triphenylacetic acid after acidification. Avoid an excess of n-butyllithium on reaction with carbon dioxide, it gives the vile-smelling pentanoic acid. 

Early investigators believed that solutions of hexaphenylethane in liquid sulfur dioxide contained both triphenylmethyl cations and triphenylmethyl anions [CcHb C ]. That equation 5 represents the correct nature of the dissociation has been demonstrated by the work of Anderson (J. Am. Chem. Soc.f 67, 1674 [1935]). He has shown that the absorption curves of hexaphenylethane and triphenylmethyl bromide in liquid sulfur dioxide are almost identical and that in dilute solution the same number of triphenylmethyl cations is obtained from one mole of hexaphenylethane as from two moles of triphenylmethyl bromide. 

Stronger bases, such as the amide ion, the hydride ion, the dimethyl sulfoxide anion, and the triphenylmethyl anion, are capable of essentially complete conversion of a ketone to its enolate ... 

If only a single electron-withdrawing substituent is present, as with simple ketones, esters, and nitriles, the formation of alkyl derivatives in high yield requires careful control of reaction conditions. Use of bases that are strong enough to effect only partial conversion of the substrate to its anion can result in aldol-condensation reactions with ketones and Claisen condensations with esters (see Chapter 2 for discussion of these reactions). This problem can be partially avoided by use of very strong bases such as the amide, hydride, or triphenylmethyl anions. 

The idea of kinetic versus thermodynamic control can be illustrated by discussing briefly the formation of enolate anions from unsymmetrical ketones. A more complete discussion of this topic is given in Chapter 7 and in Part B, Chapter 1. Any ketone with more than one type of a-proton can give rise to at least two enolates when a proton is abstracted. Many studies, particularly those of House,have shown that the ratio of the two possible enolates depends on the reaction conditions. If the base is very strong, such as the triphenylmethyl anion, and there are no hydroxylic solvents present, enolate 6 is the major product. When equilibrium is established between 5 and 6 by making enolate formation reversible by using a hydroxylic solvent, however, the dominant enolate is 5. Thus, 6 is the product of kinetic control... 

Suzuki S, Kato M, Nakajima S (1994) Application of electrogenerated triphenylmethyl anion as a base for alkylation of arylacetic ester and arylacetonitriles and isomerization of allylbenzenes. Can J Chem 72 357-361... 

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