Aromatic Nucleophilic Substitution Reactions

A considerable number of ring-fluorinated diazines undergoes various nucleophilic aromatic substitution reactions. Nucleophilic aromatic substitution reactions follow the well-established two-step addition-elimination mechanism via a Meisenheimer intermediate. The destabilization of sp -C bound fluorine by p-Jt repulsion activates fluorinated aromatic compounds toward nucleophilic attack and subsequent substitution. The susceptibility of the carbon center toward nucleophiles is also enhanced by the negative inductive (-la) effect of fluorine. Therefore the ease of nucleophilic halogen replacement - F>Cl>Br>I - is in the opposite order to that for aliphatic... 

There are many cine substitution reactions of aromatic nitro compounds using various nucleophiles.100 In this chapter, the cine-substitution reactions using the anion of nitroalkanes... 

Classical Michaelis-Arbuzov or Michaelis-Becker approaches toward formation of C-P bonds involving aromatic carbon sites are (understandably) not generally feasible. Nucleophilic substitution reactions on aromatic carbon proceed only under particular circumstances relating to the nature of attendant additional substituents, and then often with mechanisms quite different from those observed in... 

In Part 11 we concentrate on aromatic systems, starting with the basics of structure and properties of benzene and then moving on to related ciromatic compounds. We even throw in a section of spectroscopy of aromatic compounds. Chapters 7 and 8 finish up this pcirt by going into detail about substitution reactions of aromatic compounds. You find out all you ever wanted to know (and maybe more) about electrophilic and nucleophilic substitutions, along with a little about elimination reactions. 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

However, the formation of molecular complexes between nucleophile and electrophile (with a possible participation of solvents) in both electrophilic aromatic substitutions and nucleophilic aromatic substitutions is clearly expected, as shown by the conventional use of the terms electrophile and nucleophile these reactions belong to apparently different fields of organic chemistry, but the unification of the two kinds of reaction is mainly a matter of terminology and of details. 

Substitution reactions on aromatic compounds are the most important methods for the preparation of aromatic compounds. Synthesizing them from nonaromatic precursors is considerably less important. Via substitution reactions, electrophiles and nucleophiles can be introduced into aromatics. A series of mechanisms is available for this. Those that are discussed in this chapter are listed in Table 5.1. 

In certain cases, light promotes substitution reactions in aromatic compounds.34 One of the fascinating features of these reactions is an almost complete change in regioselectivity from that observed in the ground-state reactions. When the nitrocatechol ether 8.1 is irradiated in alkali or in methylamine, the nucleophilic substitution takes place meta to the nitro group. The nucleophilic substitution of p-nitroanisole 8.2, however, takes place para to the X-substituent. 

Figure 25.3. Potential energy changes during course of reaction nucleophilic aromatic substitution. Formation of carbanion is rate-controlling step strength of C--X bond docs not affect over-all rate.

Substitution reactions with aromatic compounds as nucleophiles ch22... 

For years, diaryliodonium salts have been used for the direct 18F-fluorinations in nucleophilic substitution reaction on aromatic rings [34, 35, 40, 41], The introduction of nocarrier-added [18F]fluoride into an aryl substituent of diaryliodonium salt results in a [18F]fluorinated arene and a corresponding iodoarene (Figure 14.4). 

Nucleophilic substitution reactions. Nucleophilic displacement of a halogen In compounds such as 2-acetamldo-4-chloromethylthlazole under reflux of an alkaline ethanol solution Is a straight foreward reaction (219). Nucleophilic aromatic substitution reactions are more complex but under certain conditions they can be used for single step synthesis of aryl methyl sulfides. A number of 4-methylthlo-polychlorobiphenyls were synthesized from... 

This chapter will discuss benzene and related aromatic compounds, including aromaticity and their special stability. Reactions of aromatic compounds will be discussed, including electrophilic aromatic substitution and nucleophilic aromatic substitution. 

The functional group transformations are derived from either electrophilic aromatic substitution or nucleophilic aromatic substitution reactions. The electrophilic aromatic substitution functional group transform is shown with a simple X group, where X is chlorine, bromine, nitro, or sulfonyl. The reagents are different, but the basic principle for the formation of such compounds is the same. 

Practical use is often made of the nucleophilic behaviour of jff-diketone-derived monomacrocyclic complexes. Sueh compounds undergo many reactions reminiscent of the electrophilic substitution reactions of aromatic compounds. For example, by interaction of [Ni(L1790)]I with isophthaloyl dichloride, the binuclear complex [Ni2(L1791)]l2 H20 was obtained [134], whose structure has been confirmed by X-ray diffraction (Eq. 8.56) [135],... 

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