Nucleophiles alkylations

The reactions of these nucleophilic processes are usually S 2 rather than S l. The reaction rate is methyl > ethyl > isopropyl, as with the alkyl hahdes. As the species to be alkylated becomes more nucleophilic, alkylation becomes faster, eg, a sulfur-containing anion alkylates more quickly than a phenohc anion. 

In contrast to pyridine chemistry, the range of nucleophilic alkylations that can be effected on neutral azoles is quite limited. Lithium reagents can add at the 5-position of 1,2,4-oxadiazoles (Scheme 16) (70CJC2006). Benzazoles are attacked by organometallic compounds at the C=N a-position unless it is blocked. 

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

In 2008, these authors reported a new strategy to attach chiral trans-l-arenesulfonylamino-2-isoborneolsulfonylaminocyclohexane to an achiral Frechet dendron (polyether having a repeated 3,5-dioxybenzyl structure) by a radical approach.The dendrimers obtained were successfully used in the enantioselective nucleophilic alkylation and arylation of ketones, providing... 

Not only because of their diminished electrophilic reactivity but also because of their propensity to undergo enolization and many other side reactions, nucleophilic alkylation of aliphatic aldehydes often suffers from low yields. Accordingly, the reaction that is successful for aromatic aldehydes is not necessarily successful for aliphatic aldehydes. 

Benzhydrylamine Derivatives Attachment of piperazine nitrogen directly to a benzhydryl carbon leads to a pair of compounds which show vasodilator activity, and which should be useful in disease states marked by impaired blood circulation. Reaction of piperonyl chloride (18) with a mixture of piperazine and piperazine dihydrochloride leads to the monoalkylation product (19). (It may be supposed that the mixture of free base and salt equilibrates to the monobasic salt, thus making the second amine less nucleophilic.) Alkylation of 19 by means of benzhydryl chloride then... 

By studying the effect of various a-substituents, it has been shown that the bond to the most highly substituted a carbon is preferentially cleaved and that the more nucleophilic alkyl carbon migrates to the relatively electron-poor free radical to form the carbene intermediate,... 

Even more pronounced steric effects have been observed for the free radical alkylation of protonated N-heterocyclic bases by the procedure of Minisci69, b d. Quinoline is attacked selectively in the 2- and 4-position by nucleophilic alkyl radicals in sulfuric acid. The largest radicals, t.-butyl, react exclusively in the 2-position because of steric hindrance by the peri-hydrogen when attack occurs at the 4-position. 

In addition to the direct nucleophilic alkylation of carbonyl complexes, the acylation of metallates with, e.g., carboxylic acid chlorides [73,100,102] or anhydrides [79] is a practical way of generating acyl complexes (Figure 2.4). Illustrative examples are given in Table 2.3. 

A template (68) containing two aluminium centres, one nucleophilic and the other electrophilic, accelerates nucleophilic alkylation of aldehydes. ... 

Enolate anions are ambident nucleophiles. Alkylation of an enolate can occur at either carbon or oxygen. Because most of the negative charge of an enolate is on the oxygen atom, it might be supposed that O-alkylation would dominate. A number of factors other than charge density affect the C/O-alkylation ratio, and it is normally possible to establish reaction conditions that favor alkylation on carbon. 

Because the addition steps are generally fast and consequently exothermic chain steps, their transition states should occur early on the reaction coordinate and therefore resemble the starting alkene. This was recently confirmed by ab initio calculations for the attack at ethylene by methyl radicals and fluorene atoms. The relative stability of the adduct radicals therefore should have little influence on reacti-vity 2 ). The analysis of reactivity and regioselectivity for radical addition reactions, however, is even more complex, because polar effects seem to have an important influence. It has been known for some time that electronegative radicals X-prefer to react with ordinary alkenes while nucleophilic alkyl or acyl radicals rather attack electron deficient olefins e.g., cyano or carbonyl substituted olefins The best known example for this behavior is copolymerization This view was supported by different MO-calculation procedures and in particular by the successful FMO-treatment of the regioselectivity and relative reactivity of additions of radicals to a series of alkenes An excellent review of most of the more recent experimental data and their interpretation was published recently by Tedder and... 

Rates of radical additions to alkenes are controlled mainly by the enthalpy of the reaction, which is the origin of regioselectivity in additions to unsymmetrical systems, with polar effects superimposed when there is a favorable match between the electrophilic or nucleophilic character of the radical and that of the radico-phile. For example, in the addition of an alkyl radical to methyl acrylate (2), the nucleophilic alkyl radical interacts favorably with the resonance structure 3. Polar effects are apparent in the representative rate constants shown in Figure 4.14 for additions of carbon radicals to terminal alkenes. Addition of the electron-deficient or electrophilic rert-butoxycarbonylmethyl radical to the electron-deficient molecule methyl acrylate is 10 times as fast as addition of... 

Santaniello et al.125 have N-alkylated pyrrole and indole (71) in the presence of crown-ether catalysts. The indolyl anion also behaves as an ambident nucleophile alkylation occurs at nitrogen and at C-3.126... 

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