Vicarious nucleophilic aromatic

A variation of the aromatic nucleophilic substitution process in which the leaving group is part of the entering nucleophile has been developed and is called vicarious nucleophilic aromatic substitution. 

Aromatic nitro compounds undergo nucleophilic aromatic substitutions with various nucleophiles. In 1991 Terrier s book covered (1) SNAr reactions, mechanistic aspects (2) structure and reactivity of anionic o-complexes (3) synthetic aspects of intermolecular SNAr substitutions (4) intramolecular SNAr reactions (5) vicarious nucleophilic substitutions of hydrogen (VNS) (6) nucleophilic aromatic photo-substitutions and (7) radical nucleophilic aromatic substitutions. This chapter describes the recent development in synthetic application of SNAr and especially VNS. The environmentally friendly chemical processes are highly required in modem chemical industry. VNS reaction is an ideal process to introduce functional groups into aromatic rings because hydrogen can be substituted by nucleophiles without the need of metal catalysts. 

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. 

Extension by Vicarious Nucleophilic Aromatic Substitution Synthesis of Imidazo[4,5-c]pyridines... 

The alkylation of aromatic nitro compounds by carbanions having a leaving group at the nueleophilic center is called Vicarious Nucleophilic Substitution of Hydrogen (VNS) (Seheme 36.1). This reaction is one of the scarce general processes that result in the formal nucleophilic aromatic substitution of hydrogen. 

Replacement of an aromatic fluorine atom by a carbon nucleophile is facihtated by the presence of electron-withdrawmg groups [82] (equation 44) Replacement of an activated aryl hydrogen can occur in preference to a nonactivated aryl fluorine [Si] (equation 45) in reactions known as vicarious subsututions. 

The 2-alkylene-substituted aromatic nitro compound 1011, which is readily accessible via vicarious nucleophilic substitution (VNS) [88-90] of 4-fluoronitroben-... 

Some derivatives of the [l,2,4]triazolo[4,3-3]pyridazine ring system 33 were subjected to a special type of nucleophilic substitution called vicarious nucleophilic substitution (VSN) <2006TL4259>. In the course of this transformation a formal substitution of az aromatic hydrogen atom - occurring via an addition-elimination mechanism - takes place. 

For the chemist practicing polysubstituted aromatic and heteroaromatic synthesis, methods steeped in classical electrophilic (1, Scheme 1) [1] and nucleophilic substitution [2] and SRN1 (2) [3] reactions have been joined and, not infrequently super-ceded, by vicarious substitution (3) [4] and by DoM (4) [5] processes. The Murai ortho CH activation (5) [6] is a recently evolving and potential competitive method to the DoM tactic. The 60 years since its discovery by Wittig and Gilman, and 40 years since its systematic study by the school of Hauser, the DoM reaction has advanced by the contributions of Christensen, Beak, Meyers, and many other... 

Abstract Synthesis methods of various C- and /V-nitroderivativcs of five-membered azoles - pyrazoles, imidazoles, 1,2,3-triazoles, 1,2,4-triazoles, oxazoles, oxadiazoles, isoxazoles, thiazoles, thiadiazoles, isothiazoles, selenazoles and tetrazoles - are summarized and critically discussed. The special attention focuses on the nitration reaction of azoles with nitric acid or sulfuric-nitric acid mixture, one of the main synthetic routes to nitroazoles. The nitration reactions with such nitrating agents as acetylnitrate, nitric acid/trifluoroacetic anhydride, nitrogen dioxide, nitrogen tetrox-ide, nitronium tetrafluoroborate, V-nitropicolinium tetrafluoroborate are reported. General information on the theory of electrophilic nitration of aromatic compounds is included in the chapter covering synthetic methods. The kinetics and mechanisms of nitration of five-membered azoles are considered. The nitroazole preparation from different cyclic systems or from aminoazoles or based on heterocyclization is the subject of wide speculation. The particular section is devoted to the chemistry of extraordinary class of nitroazoles - polynitroazoles. Vicarious nucleophilic substitution (VNS) reaction in nitroazoles is reviewed in detail. 

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