Groups electron-withdrawing

Both precursors can be used as reactants in an aldol condensation. It has to be emphasized that the chlorine atom in 4 has to be considered as a representative for any electron-withdrawing group in particular, in the case presented here, it would best be taken as an OEt group. In order to verify this proposal, a reaction substructure search is initiated in the Chcmlnform reaction database of 1997. 

Note that the Diels-Alder reaction works best when there is an electron-withdrawing group (here CC>2Et) on the olefinic component. 

A cyclohexene with an electron-withdrawing group on the other side of the ring to the double bond ... 

Alkyllithium bases are generally less suitable for deprotofiation of compounds with strongly electron-withdrawing groups such as C=0, COOR and CsN. In these cases lithium dialkylamides, especially those with bulky groups (isopropyl, cyclohexyl), are the reagents of choice. They are very easily obtained from butyllithium and the dialkylamine in the desired solvent. 

The electrophilicity of C = C double bonds conjugated with electron withdrawing groupings leads to a -synthons. This is an important example of the vinyiogous principle ... 

If alkyl groups are attached to the ylide carbon atom, cis-olefins are formed at low temperatures with stereoselectivity up to 98Vo. Sodium bis(trimethylsilyl)amide is a recommended base for this purpose. Electron withdrawing groups at the ylide carbon atom give rise to trans-stereoselectivity. If the carbon atom is connected with a polyene, mixtures of cis- and rrans-alkenes are formed. The trans-olefin is also stereoseiectively produced when phosphonate diester a-carbanions are used, because the elimination of a phosphate ester anion is slow (W.S. Wadsworth, 1977). 

The electronic influence of the 4-substituent corresponds to a relative increase in the kinetic acidity of the C-5 proton when an electron-withdrawing group (R=Ph) is situated at the 4-position and to a relative increase in the kinetic acidity of the 2-methyl group when an electron-donating group (R = Me) is at the same position (Table 1-59). 

Aldehydes are more generally prepared by electrolytic reduction of amides, the reduction of carboxylic adds being possible only when they are activated by a strongly electron-withdrawing group (58). 

As an electron withdrawing group on a carbon-carbon double bond a carbonyl group renders the double bond susceptible to nucleophilic attack... 

Nucleophilic substitution m ArX is facilitated by the presence of a strong electron withdrawing group such as NO2 ortho or para to the halogen... 

Multiple substitution by strongly electron withdrawing groups greatly increases the acidity of phenols as the values for 2 4 dimtrophenol (4 0) and 2 4 6 trimtrophenol (0 4) m Table 24 2 attest... 

Electron releasing substituents attached to the ring have a negligible effect on the acidity of phenols Strongly electron withdrawing groups increase the acidity The compound 4 nitro 3 (tnfluoromethyl)phenol for example is 10 000 times more acidic than phenol... 

Methylene derivatives ate readily formed in the vapor phase with compounds having a hydrogen in the alpha position to an electron-withdrawing group. Acryhc (40,41) and methacrylic (42) acids (or esters) are produced at 300—425°C from acetic and propionic acids (or esters), respectively, using alkafl and... 

Synthetic and mechanistic aspects of iatramolecular cycli2ation in the tricycHc diterpenoid area have been studied in detail. In general, the presence of electron withdrawing groups such as carbonyl in the side chain retard the rates of cycli2ation (61). 

Hydroxybenzaldehydes readily react with compounds containing methyl or methylene groups bonded to one or two carboxyl, carbonyl, nitro, or similar strong electron-withdrawing groups. The products are usually P-substituted styrenes. 4-Hydroxybenzaldehyde, for example, reacts with 2-methylquinazolines (where R = H, Cl) to give compounds which have anti-inflammatory activity (59). 

Hydroxyalkyl Alkyl Peroxides and Hydroxyalkyl Peroxyesters. The same stmctural restrictions discussed for the hydroxyhydroperoxides apply for the hydroxyalkyl alkyl peroxides, and those that exist are derived from aldehydes and certain ketones having electron-withdrawing groups, eg, polyfluorinated a,P-unsaturated ketones (136). 

As a variation on the base-catalyzed nucleopbilic displacement chemistry described, polysulfones and other polyarylethers have been prepared by cuprous chloride-catalyzed polycondensation of aromatic dihydroxy compounds with aromatic dibromo compounds. The advantage of this route is that it does not require that the aromatic dibromo compound be activated by an electron-withdrawing group such as the sulfone group. Details of this polymerization method, known as the Ullmaim synthesis, have been described (8). 

Mono- and dialkyl derivatives can also be prepared using alkyl sulfates. Aryl chlorides are usually inert, unless activated by an electron-withdrawing group. Conversion to alkoxides allows formation of ethers. 

A tertiary carbonium ion is more stable than a secondary carbonium ion, which is in turn more stable than a primary carbonium ion. Therefore, the alkylation of ben2ene with isobutylene is much easier than is alkylation with ethylene. The reactivity of substituted aromatics for electrophilic substitution is affected by the inductive and resonance effects of a substituent. An electron-donating group, such as the hydroxyl and methyl groups, activates the alkylation and an electron-withdrawing group, such as chloride, deactivates it. 

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