Reactions, complementary nucleophilic

Allylic alkylation (cf., 12,557). This W(0) complex in combination with 2,2 -bipyridyl (bpy) catalyzes reactions of nucleophiles with allylic acetates or carbonates, but the chemoselectivity is complementary to that of Pd(0), as shown in equation (I). The W(0)-catalyzed reactions are influenced by inductive and steric... 

Fluorinated -alkenes and -cycloalkenes have a special relationship with their hydrocarbon analogues, usually exhibiting a chemistry that is complementary. For example, the fluorinated systems are frequently susceptible to nucleophilic attack, in some cases dramatically so, and therefore reactions of nucleophiles with fluorinated alkenes often reveal unique new chemistry. This chapter covers electrochemical reduction, principles governing orientation and reactivity of fluorinated alkenes towards nucleophiles, fluoride ion as a nucleophile and the mirror-image relationship of this chemistry with that of proton-induced reactions, reactions with nitrogen-, oxygen-, carbon- centred nucleophiles etc., and, finally, chemistry of some oligomers of fluorinated -alkenes and -cycloalkenes. 

First, the preparation of the substituted benzene 172 is explained. In the reaction of substituted benzene complex 175 with carbanions, the meta orientation to give 176 is observed even in the presence of ortho- and para-orienting electron-donating groups, such as methoxy and amino groups [45], Using this property, the nucleophilic substitution reaction, complementary to ordinary electrophilic substitution reaction, is... 

A complementary part to the reaction with neutral, although polarized, vinylic carbon is the reaction of nucleophiles with vinyl cations 14 (equation 5). The data in this case are much more limited, for two reasons (1) very few vinyl cations had been prepared with sufficiently long lifetime that allows their direct reaction with nucleophiles to be followed and (2) a very few capture experiments of a solvolytically generated vinyl cation by several nucleophiles were conducted. 

The study of the interaction of drugs with cellular components can be broken down into two types of experiments, either measurement of covalent binding after reaction with nucleophilic sites on cellular macromolecules or studies with small molecule nucleophiles. These two types of experiments provide complementary information and are probably both important determinants in the overall toxicology associated with reactive intermediates. 

Enantiosdective allyic substitution processes have been developed over the course of 30 years. Initial observations of the reactions of nucleophiles with paUadium-allyl complexes led to the observation of catalytic substitutions of aUylic ethers and esters, and then catalytic enantioselective aUylic substitutions. The use of catalysts based on ottier metals has led to reactions that occur with complementary regiochemistry. Moreover, flie scope of the reactions has expanded to include heteroatom and unstabilized carbon nucleophiles. Suitable electrophiles for these reactions indude allyhc esters of various types, allyhc ethers, aUylic alcohols, and aUylic halides. Enantioselective reactions can be conducted with monoesters or by selection for deavage of one of two equivalent esters. The mechanism of these reactions occurs by initial oxidative addition to form a metal-aUyl complex. The second step involves nudeophilic attadc on ttie aUyl ligand for reaction of "soft" nudeophiles or inner-sphere reductive eUmination for reactions of "hard" nudeophiles. The external nudeophilic attack typicaUy occurs by reaction of the nudeophile with a cationic aUyl complex at the face opposite to that to which Uie metal is bound. Exceptions indude reactions of certain molybdenum-aUyl complexes. Dissociation of product then regenerates the starting catalyst. Because of the diversity of the classes of these reactions, aUylic substitution—in particular asymmetric aUylic substitution—has been used to prepare a wide variety of natural products. 

Figure 7.8 The reaction of ethynide (acetylide) anion and chloromethane. Electrostatic potential maps illustrate the complementary nucleophilic and electrophilic character of the alkynide anion and the alkyl halide. The dipole moment of chloromethane is shown by the red arrow.

Because the pK s of the aldehyde and water are similar, the solution contains significant quantities of both the aldehyde and its enolate. Moreover, their reactivities are complementary. The aldehyde is capable of undergoing nucleophilic addition to its carbonyl group, and the enolate is a nucleophile capable of adding to a carbonyl group. And as shown in Figure 18.4, this is exactly what happens. The product of this step is an alkoxide, which abstracts a proton from the solvent (usually water or ethanol) to yield a (3-hydroxy aldehyde. A compound of this type is known as an aldol because it contains both an aldehyde function and a hydroxyl group (aid + ol = aldol). The reaction is called aldol addition. 

A mild and efficient a-heteroarylation of simple esters and amides via nucleophilic aromatic substitution has been described <06OL1447>. Treatment of 2-chloro-benzo[//Jthiazole 99 with tert-butyl propionate in the presence of NaHMDS under nitrogen furnishes tert-butyl 2-(benzo[c(jthiazol-2-yl)propanoate 100. When the same reaction is preformed initially under nitrogen and then exposed to air, the hydroxylation product 101 is obtained. This method offers two desirable features that are either complementary or improvements to the palladium-catalyzed a-arylation reactions. First, heteroaryl chlorides... 

The number of nucleophilic sites per macromolecule n can be established from kinetic measurements in the presence of excess substrate and complementary ones in the presence of excess polymer.48 In the decarboxylation of oxalacetate, n is 90 at pH 4.5 and 150 at pH 7.0. The modified polyethylenimine polymer used contains 140 primary amine groups per macromolecule. Thus 65 to 100% of these act as nucleophilic sites for the decarboxylation reaction. 

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