Alkylate anions

The Grignard reagent RMgX is nucleophilic by virtue of the potential car banion (alkyl anion) R. It will react with the electrophilic carbonyl group as follows ... 

Ordinarily nucleophilic addition to the carbon-carbon double bond of an alkene is very rare It occurs with a p unsaturated carbonyl compounds because the carbanion that results IS an enolate which is more stable than a simple alkyl anion... 

Enarnioselective nitro-dlclol reacdon Csee Secdon 3.3 or Michael reaction Csee Secdon 4.4 followed by radical denitration is useful as an altemadve indirect method of enandose-lecdve 1,3- or 1,4-addidon of alkyl anions fsee Eq. 7.70 and Eq. 7.71 . ... 

Although this method is aot a geaeral procedure, bemg specific for ct-nitroketoues, k has several merits to avoid the use of toxic reageuts such as organodn compounds Functionalized ketones have been prepared by this denitration reaction, in which functionalized nitroalkanes are used as alkyl anion synthons For example, 3-nitropropanal ethylene acetal can be used as synthon of the 3-oxo-propyl anion and 1,4-dicarbonyl compounds are prepared, as shovm In Eq 7 88... 

Evidence in support of a carbocation mechanism for electrophilic additions comes from the observation that structural rearrangements often take place during reaction. Rearrangements occur by shift of either a hydride ion, H (a hydride shift), or an alkyl anion, R-, from a carbon atom to the adjacent positively charged carbon. The result is isomerization of a less stable carbocation to a more stable one. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

One-electron reduction of the iron(lll) alkyl complexes forms the diamagnetic iron(ll) alkyl anions [Fe(Por)R. The iron(ll) anions do not react with oxygen directly, but are first oxidized by O2 to the corresponding alkyliron(III) complexes, Fe(Por)R, which then insert O2 as described above. 

Iron(II) alkyl anions fFe(Por)R (R = Me, t-Bu) do not insert CO directly, but do upon one-electron oxidation to Fe(Por)R to give the acyl species Fe(Por)C(0)R, which can in turn be reduced to the iron(II) acyl Fe(Por)C(0)R]. This process competes with homolysis of Fe(Por)R, and the resulting iron(II) porphyrin is stabilized by formation of the carbonyl complex Fe(Por)(CO). Benzyl and phenyl iron(III) complexes do not insert CO, with the former undergoing decomposition and the latter forming a six-coordinate adduct, [Fe(Por)(Ph)(CO) upon reduction to iron(ll). The failure of Fe(Por)Ph to insert CO was attributed to the stronger Fe—C bond in the aryl complexes. The electrochemistry of the iron(lll) acyl complexes Fe(Por)C(0)R was investigated as part of this study, and showed two reversible reductions (to Fe(ll) and Fe(l) acyl complexes, formally) and one irreversible oxidation process."" ... 

Energy-resolved CID can be used to measure bond dissociation energies directly, and therefore is readily applicable for the determination of ion affinities. However, Graul and Squires have also described a method for measuring gas-phase acidities using CID of carboxylates. ° Upon CID, carboxylate ions, RCO2, undergo decarboxylation to form the alkyl anions, R, ... 

Enantioselective nitro-aldol reaction (see Section 3.3) or Michael reaction (see Section 4.4) followed by radical denitration is useful as an alternative indirect method of enantioselective 1,2- or 1,4-addition of alkyl anions (see Eq. 7.7087 and Eq. 7.7188). 

Alkenylation using nitroalkanes followed by the selective reduction of the double bonds with NiCl2 and NaBH4 can be regarded as the addition of alkyl anions to electron-deficient alkenes (Eq. 7.127).173... 

Anionic polymerization can be initiated by a variety of anionic sources such as metal alkoxides, aryls, and alkyls. Alkyllithium initiators are among the most useful, being employed commercially in the polymerization of 1,3-butadiene and isoprene, due to their solubility in hydrocarbon solvents. Initiation involves addition of alkyl anion to monomer... 

Nitroalkane can be used as a convenient reagent for alkyl anion synthesis. Aliphatic nitro compounds can also be considered as versatile building blocks and intermediates in organic synthesis. They are readily available, and there are a wide variety of methods for converting the nitro group to other functional groups. 

Ionic or partially ionic compounds can be chromatographed on reversed-phase columns through the use of ion-pairing reagents. These reagents are typically long-chain alkyl anions or cations that, in dilute concentrations, can increase the retention of analyte ions. For cationic compounds, C5 to CIO alkyl sulfonates are commonly used combinations may also be used... 

These Sn/Li transmetallations involve nucleophilic attack of an alkyl anion at the tin center. Transmetallations with metal halides on the other hand involve electrophilic attack of the metal at the allylic double bond. 

The n type carbanions undergo most of the reactions given by o alkyl anions. An example is... 

The electrocyclic reactions of n systems containing an impaired electron are difficult to interpret using the above simple theories. The symmetry of the HOMO of the radical system corresponds to that of the corresponding anion. Thus the allyl radical would be expected to cyclize in the same manner as the alkyl anion i.e., in a conrotatory manner. In fact the interconversion takes place in a disrotatory manner. Theoretical calculations based on Huckets theory also give ambiguous or incorrect predictions. And therefore more sophisticated calculations are required to obtain reliable results. 

An extensive review on the use of nitroalkanes as alkyl anion synthons has appeared415. 

The first steps involve coordination and cycloaddition to the metal. Insertion of a third molecule of ethene leads to a more instable intermediate, a seven-membered ring, that eliminates the product, 1-hexene. This last reaction can be a (3-hydrogen elimination giving chromium hydride and alkene, followed by a reductive elimination. Alternatively, one alkyl anion can abstract a (3-hydrogen from the other alkyl-chromium bond, giving 1-hexene in one step. We prefer the latter pathway as this offers no possibilities to initiate a classic chain growth mechanism, as was also proposed for titanium [8]. The byproduct observed is a mixture of decenes ( ) and not octenes. The latter would be expected if one more molecule of ethene would insert into the metallocycloheptane intermediate. Decene is formed via insertion of the product hexene into the metallo-cyclopentane intermediate followed by elimination. 

Vitamin Bi2-catalyzed intramolecular cathodic coupling leads to a regioselective 1,4-addition with formation of a spirocom-pound (Eq. 2) [95]. This chain reaction is initiated by the reduction of Co(III) to a Co(I) species, which reacts in an oxidative addition with the alkyl bromide. The resulting alkyl-Co(III)-Br species is then reduced to an alkyl anion that undergoes a Michael addition and yields Co(I) for the next cycle. 

Sn2 substitution reactions of alkyl halides with hard nucleophiles such as alkyl anions can be achieved most readily with the aid of organocopper chemistry [95]. Sn2 reactions with epoxides and aziridines are also synthetically useful [96]. The... 

Let us follow the role of steric hindrance in a forming product during the course of process according to Komblum and Erickson (1981) as well as Akbulut et al. (1982). Scheme 6.5 clearly demonstrates the effect here, all of the constituent reactions were performed in equal conditions (HMPA as a solvent, at 25°C). The nature was proven for all the cases. The intermediary cumyl radical reacts with the nitroalkane anion, but this reaction is retarded with an increase in the size of an alkyl anion. The significance of the cumyl radical dimerization grows accordingly. 

Several workers have concluded that under conditions used in their study ion-pairing in the mobile phase between amphiphilic hetaeron ions and oppositely charged sample components governed retention. Horvath et al. (34) examined the effect of alkyl sulfates and other alkyl anions on the retention of catecholamines in which both the concentration and the length of the alkyl chains of the hetaerons were varied. The hyperbolic concentration dependence of the retention factor shown in Fig. 48, was found to be similar to that reported by others. 

Alkylation involves transfer of an alkyl anion to the propagating center. Hydridation involves transfer of a hydride ion from the alkyl anion to the propagating center. Hydridation occurs in preference to alkylation when the trialkylaluminum contains P-hydrogens. 

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