Synthesis via nucleophilic aromatic

Figure 12.2 General reaction scheme for the benzimidazole synthesis via nucleophilic aromatic substitution.

Most syntheses of naturally occurring phenazines, though, are based on a two-step elaboration of the central heterocycle of the phenazine [78]. The first key step involves the generation of orf/zo-monosubstituted 88 or orf/zo, ortho -disubstituted diphenylamines 89-91 via nucleophilic aromatic substitution. Ring formation is then achieved by means of reductive or oxidative cyclization, for which a number of efficient methods are available. The main flaw of this approach is the synthesis of the substituted diphenylamines via nucleophilic aromatic substitution, as this reaction often can only be performed under strongly basic reaction conditions and at high temperatures. In addition, the diphenylamines required may only be achieved with certain substitution patterns with high yields. 

A. Plenevaux, J.S. Fowler, S.L. Dewey, A.P. Wolf, M. Guillaume, The synthesis of no-carrier-added dl-4-C Fjfluorodeprenyl via nucleophilic aromatic substitution reaction, Int. J. Radiat. Appl. Instrument. Part A, Appl. Radiat. Isot. 42 (1991) 121-127. 

The regioselective functionalization of nitrobenzene and benzonitrile derivatives has been performed via nucleophilic aromatic substitution of hydrogen by phosphorus-stabilized carbanions.41 Lithium phosphazenes have been found to be the most suitable nucleophiles for the substitution of hydrogen in nitrobenzene. This method represents a convenient alternative to the vicarious nucleophilic substitution for the synthesis of benzylic phosphorus derivatives using phosphorus-stabilized anions that do not bear a leaving group at the carbanionic centre. 

Figure 13. Synthesis of 4-methylthio-2,2, 5,5 -tetrachloro-biphenyl via nucleophilic aromatic substitution.

Bergman, A. and C.A. Wachtmeister. 1978. Synthesis of methylthio- and methylsul-phonyl-polychlorobiphenyls via nucleophilic aromatic substitution of certain types of polychlorobiphenyls. Chemosphere 7 949-956. 

Synthesis via coupling aromatic diazonium salts with carbon nucleophilic 4 atom fragments... 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

The next step of this investigation was to examine the polymerization of monomer 19 via nucleophilic aromatic substitution reactions with dinucleophiles 14a and 14b. Scheme 10 shows the synthesis of polymers 22a and 22b using this methodology. 

Scheme 3.30 Solid-phase synthesis of heteroaryl azides via nucleophilic aromatic substitution" ...

The same group has reported another example using four-component Ugj reaction followed by a postcondensation cyclization via nucleophilic aromatic substitution (SnAt) leading to a two-step synthesis of imidazo- and pyrazolo[l,5-fl]quinoxalines [129] (Scheme 93). The Ugi reaction is initiated by the condensation of amine with... 

The acidic character of the hydrogen atoms of C-methyl groups linked to the pyrazolium ring (Figure 22 Section 4.04.2.1.1(11)) facilitates a number of reactions difficult to carry out with neutral pyrazoles. Since efficient methods of dealkylation have been described (Section 4.04.2.3.lO(ii)), the synthesis via the pyrazolium salt is a useful alternative. The same behaviour is observed for indazolium salts, for example, nucleophilic addition to aromatic aldehydes (78JOC1233). 

The most practical method for the preparation of polyfarylcnc ether)s employs nucleophilic aromatic substitution (SnAi). Although nucleophilic substitution can occur via four principal mechanisms,49 the most important mechanism utilized for the synthesis of poly(arylene etlier)s has been SnAt, in which activating groups are present on the aromatic ring (Scheme 6.10). 

Smith, Jason A., 431 Sn2+ compounds, 233 Sn4+ compounds, 232 SNAr reaction. See also Nucleophilic aromatic substitution reaction poly(arylene ether sulfone) synthesis via, 336-340... 

In recent years, the importance of aliphatic nitro compounds has greatly increased, due to the discovery of new selective transformations. These topics are discussed in the following chapters Stereoselective Henry reaction (chapter 3.3), Asymmetric Micheal additions (chapter 4.4), use of nitroalkenes as heterodienes in tandem [4+2]/[3+2] cycloadditions (chapter 8) and radical denitration (chapter 7.2). These reactions discovered in recent years constitute important tools in organic synthesis. They are discussed in more detail than the conventional reactions such as the Nef reaction, reduction to amines, synthesis of nitro sugars, alkylation and acylation (chapter 5). Concerning aromatic nitro chemistry, the preparation of substituted aromatic compounds via the SNAr reaction and nucleophilic aromatic substitution of hydrogen (VNS) are discussed (chapter 9). Preparation of heterocycles such as indoles, are covered (chapter 10). 

Aromatic nitrations, 17 160-161 by-products of, 17 161 kinetics of, 17 162 Aromatic nitriles, 17 243 Aromatic nucleophilic displacement, polyimide synthesis via, 20 273 Aromatic phosphines, 19 60, 62 Aromatic poly(monosulfide ketone)s, 23 709 Aromatic poly(monosulfide)s, 23 706 Aromatic polyamide copolymers, laboratory synthesis of, 19 720 Aromatic polyamide fibers, 24 614 Aromatic polyamides, 10 210-212 19 713-738. See also Aliphatic polyamides (PA)... 

Kotsuki [128] reported a straightforward approach to the synthesis of chiral 4-PPY (35, Fig. 7) catalysts via high-pressure promoted nucleophilic aromatic... 

This reaction is a powerful tool and represents an alternative for the synthesis of substituted arenes difficult to prepare via classical electrophilic or nucleophilic aromatic substitution. Using bi- or polyfunctional arenes as starting materials, this reaction affords novel organoiron polymers [76] (Scheme 1.35). 

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