Anions reaction with electrophiles

Organic anions (Reactions with electrophiles formation of basic species)... 

However, it can be expected that anions of allyl sulfoxides maintain, at low temperature, the chiral integrity of the sulfoxide group and that reactions with electrophiles could have regio-and stereochemical implications. 

The decarboxylation reaction usually proceeds from the dissociated form of a carboxyl group. As a result, the primary reaction intermediate is more or less a carbanion-like species. In one case, the carbanion is stabilized by the adjacent carbonyl group to form an enolate intermediate as seen in the case of decarboxylation of malonic acid and tropic acid derivatives. In the other case, the anion is stabilized by the aid of the thiazolium ring of TPP. This is the case of transketolases. The formation of carbanion equivalents is essentially important in the synthetic chemistry no matter what methods one takes, i.e., enzymatic or ordinary chemical. They undergo C—C bond-forming reactions with carbonyl compounds as well as a number of reactions with electrophiles, such as protonation, Michael-type addition, substitution with pyrophosphate and halides and so on. In this context,... 

This reaction was interpreted as a chain process. The major reaction is accompanied by two side processes (Scheme 3.239), such as O -alkylation of the anion C with electrophilic nitrosoalkene (reaction b) giving rise to oximes (445) and (446) and the addition of the target oxime (443) to the second molecule of nitrosoalkene B producing dioxime (447) (reaction d). 

The diazeniumdiolate anions react with electrophiles to produce stable covalent compounds (Fig. 3.9) [213, 216]. These compounds have the ability to act as prodrugs, releasing nitric oxide only when metabolically or enzymatically converted to the diazeniumdiolate anion [217-219]. Several compounds ofthis class have been synthesized by reaction of alkyl or aryl halides, sulfate esters, epoxides, etc. with the ionic diazeniumdiolates [220, 221]. 

Stannyllithium compounds are important as sources of nucleophilic stannyl anions, and the dialkyltin lithium hydrides, R2SnLiH, have recently come to prominence as their reaction with electrophilic alkyl halides gives hydrides, R1R2SnH, with mixed alkyl groups (see Section 3.14.18.1).397... 

The chemistry of reaction of the highly reactive l-trimethylsilylcyclopropan[fc]naph-thalen-l-ide anion (126) with electrophiles has been explored.The anion can be trapped as the 1-methyl-1-trimethylsilyl derivative (128) [along with some (121) and (124)] when generated from (129) by action of Bu 0 -THF in the presence of iodomethane. If (126) is formed by action of H0 -H20 on (129) it is converted quantitatively into cyclopropanaphthalene (121) but can be trapped by carbonyl compounds such as benzophenone, fluoren-9-one, or 4-(dimethylamino)benzaldehyde. 

TELLURIUM-MEDIATED FORMATION OF ANIONIC SPECIES AND THEIR REACTIONS WITH ELECTROPHILES... 

Picoline and 4-picoline are easily deprotonated as the conjugate car-banions are resonance stabilized. These anions can be used in alkylations and other reactions with electrophiles (Scheme 2.20). 

Pyrrole can be deproionated by strong bases, forming the resonance-stabilized pyrrolyl anion. The anion is susceptible to reactions with electrophiles, the location depending upon the reagent and the conditions. 

The 2-azaallyl anions 2 obtained were used for 1,3-dipolar cycloadditions mostly to give five-membered rings 3, but reaction with electrophiles at the former A-alkyl carbon atom to give 4 has also been described. 

The anion 7 is quite nucleophilic and undergoes exclusive C-alkylation upon reaction with electrophiles including chlorotrimethylsilane °. These reactivity patterns have led to the suggestion that enolates of iron-acyl complexes may be considered to behave similarly to the organic dianion 910- u. 

The generation of the anions from the lactim ethers and their reaction with electrophiles is deferred to the next section. 

Electrophilic attack at ring heteroatoms is rare for the neutral compounds, although examples are known for thiophenes and selenophenes. However, pyrrole anions undergo easy reaction with electrophiles at both C and N atoms. 

Pyrroles, indoles, isoindoles and carbazoles having no substituent at the nitrogen atom are weakly acidic and, upon treatment with a strong base, form anions which are capable of subsequent reaction with electrophiles at the nitrogen atom and/or the 1-position of isoindoles, the 2-position of pyrroles and the 3-position of indoles. 1-Substituted pyrroles and indoles also react with butyllithium to give 1-substituted 2-pyrrolyl and 2-indolyl anions (see Section 3.05.1.2.9). 

Ketone dilithio-c /S-dianions (30, formed by treatment of /3 -stannylketones, RCOCH2-CH2SnBuCl2, with 4 equiv. of BuLi) react with imines and hydrazone selectively at the /3-anion portion to give dilithium enolate amides (31).82 Subsequent reaction with electrophiles gives y-amino ketones and related heterocycles. 

It is not usually possible to form mixed JVO-donor ligands by direct reaction of co-ordinated 1,3-diketonates with amines. In part, this is due to the delocalised charge of the formally anionic ligand rendering the diketonate less prone to attack by a nucleophile. This deactivation towards attack by nucleophiles should be contrasted with the facile reactions with electrophiles which have been discussed in Section 5.3. It is possible, however, to form complexes of conjugated /VO-donor ligands by direct reaction of the metal-free, 1,3-dicarbonyl with amine, followed by co-ordination (Fig. 5-48). 

O. Hammerich, M. F. Nielsen, The Competition Between the Dimerization of Radical Anions and Their Reactions with Electrophiles, Acta Chem. Scand. 1998, 52, 831-857. 

The lithiated bis-lactim ether (52) in which benzyl at the inducing center is replaced by phenyl, reacts with electrophiles considerably less stereospecifically (Table 8)20. Since phenyl is commonly regarded as bigger than benzyl — although the apparent size of a group depends very much on the reacting system — this finding seems to be consistent with the folded conformation 43 of the anion and the transition state of it s reactions with electrophiles. 

In an interesting new application, benzynes have been generated from the 2-fluoroalkylanines 78, and underwent anionic cyclization, followed by reaction with electrophiles to furnish a variety of 4-substituted indoles 79 <02CEJ2034>. 

Some tellurium compounds can mediate the formation of anionic species and their reactions with electrophiles.6 10 12 118 Some examples are given in the following. 

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