Pyridine Vicarious nucleophilic substitution

Intramolecular substitution of chlorine in 3-[iV-alkanesulfonyl-iV-alkyl)-amino-2-chloropyridines 455 affords pyridosultams 456 (see Section 4.05.6.3.2) <2000EJ01263, 1997TL4667>. The application of intramolecular vicarious nucleophilic substitution of hydrogen in A -oxides and quaternary salts of chloromethansulfonamides 457 (R =0, Me R = R = H) afforded isothiazolo[4,3-/ ]pyridines 458 and 459. Starting from 3-aminoquinoline 457 (R -R = -CH=CH-CH=CH-), the corresponding compounds 458 and 459 were obtained <2001T5009>. 

In a so-called vicarious nucleophilic substitution of hydrogen,75 2,3-diphenylpyrido[2,3-6]-pyrazine is alkylated in the 8-position by [(chloromethyl)sulfonyl]benzene. This reaction proceeds by addition of the carbanion to the electron-deficient ring position of a nitroarene or electrophilic heteroaromatic system, followed by base-induced -elimination of the corresponding hydrogen halide.76,77 As with quinoxalines and naphthyridines, the reaction with pyrido[2,3-6]pyrazines also affords products bisannulated at the pyrazine or the pyridine moiety, depending on the kind of 2/3-substitution (cf. Section 7.2.3.1.2.2.2.). 

Another approach exploits vicarious nucleophilic substitution (VNS) [76]. Indeed, efficient syntheses of isothiazolo[4,3-h]pyridines and isothiazolo[4,3-I ]-quinolines have been advanced via intramolecular VNS of hydrogen in pyridine and quinoline... 

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

Keywords Alkyl hydroperoxides Amination Ammonia Benzimidazole Benzisoxazole Carbanions Heterocycles Hydroxylation Indole Nitro compounds Nucleophiles Nucleophilic substitution Oxidation Phenazine Potassium permanganate Pyridine Quinoline Sulfones Vicarious... 

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