Other Nucleophilic Substitution Reactions

As m other nucleophilic substitution reactions alkyl p toluenesulfonates may be used m place of alkyl halides... 

Displacement by cyanide works particularly well, and many other nucleophilic substitution reactions are enhanced by PTC. Most monovalent anions can be transferred, including alkoxides, phenoxides, thiocyanates, nitrates, nitrites, superoxides and all of the halides. Divalent anions are usually too hydrophilic to be transferred into the organic phase. 

The utility of this simple transformation is often to increase the reactivity of the substrate, in that halide is a good leaving group and so can participate in other nucleophilic substitution reactions. 

Finally, these mechanistic proposals can be easily generalized to other nucleophilic substitution reactions ... 

Two other nucleophilic substitution reactions of pyridine iV-oxides deserve mention and further study to determine the effects of substituents. Pyridine N-oxide, benzoyl chloride, and the piperidine enamine of cyclohexanone give a good yield of 2-(2 -pyridyl)cyclo-hexanone (155) (63%).360 When W-methoxy-4-picolinium methyl... 

Although they really belong in Chapter 17 with other nucleophilic substitution reactions, we included the last few examples of epoxide-opening reactions here because they have many things in common with the reactions of bromonium ions. Now we are going to make the analogy work the other way when we look at the stereochemistry of the reactions of bromonium ions, and hence at the stereoselectivity of electrophilic additions to alkenes. We shall first remind you of an epoxide reaction from Chapter 17, where you saw this. 

Like these other nucleophilic substitution reactions, ammonolysis is limited chiefly to alkyl halides or substituted alkyl halides. As with other reactions of this kind, elimination tends to compete (Sec. 14.23) with substitution ammonia can attack... 

Halogen-containing indoles can be subjected to other nucleophilic substitution reactions under the guidance of palladium. Thus, 1-bromonauclefine is smoothly debromi-nated to nauclefine with Pdt Ph.P) (96%) [206], and 5-haloindoles are converted to... 

On the other hand, polymeric beads of supported ILs ( polymer-supported imidazolium salt, PSIS) were also prepared via the covalent anchoring of an imidazolium salt to a polystyrene resin.These PSISs, which have the advantage of significantly enhancing the nucleophilicity of metal salts compared with conventional methods, have been used as efficient catalysts for nucleophilic fiuorination and for other nucleophilic substitution reactions. In particular, the authors found that the applied PSIS had many practical merits product recovery and purification was simple and catalyst recovery and reuse were easy (Figure 4.12). 

Other Nucleophilic Substitution Reactions. Nucleophilic substitution of a variety of substituted aminoiminomethanesulfonic acids with cyanide leads to the corresponding aminoimi-noethanenltrlles in 30-87% yield. A number of substituted aminoiminomethanesulfonic acids react with sodium azide in acetic acid to give the corresponding 5-aminotetrazole. This reaction Is subject to pronounced steric hindrance. Hydroxyl-amine and cyanamlde also give nucleophilic substitution of the sulfonic acid group. ... 

S-Adenosylmethionine then acts as the substrate for other nucleophilic substitution reactions. In the biosynthesis of choline, for example, it transfers its methyl group to a nucleophilic nitrogen atom of 2-(N,N-dimethylamino)ethanol ... 

In other nucleophilic substitution reactions, the rate of the reaction depends only on the concentration of the substrate, not on that of the nucleophile. These imimolecular reactions, designated S l, occur in two steps. In the first step, the bond between the carbon atom and the leaving group breaks to produce a carbocation and a leaving group. In the second step, the carbocation reacts with the nucleophile to form the product. The first step in an S jl reaction, formation of a carbocation, is the slow, or rate-determining step. The second step, formation of a bond between the nucleophile and the carbocation, occurs very rapidly. Since the slow step of the reaction involves only the substrate, the reaction is a first-order process. 

In addition to being catalysts for triphasic cyanation reactions, organo hectorite assemblies catalyze a variety of other nucleophilic substitution reactions. Equations 2-6 below illustrate the diverse range of reactions that can be catalyzed by [(n-CgHi7)3NMe]+- hectorite. Reaction conditions and chemical yields for each conversion are provided in Table II. 

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