Vicarious substitution

In contrast, reaction of 82 with NaCN in DMF-H2O at reflux results in the formation of 7-cyano-6-nitroindole (201, 15%) and 83 (4%) as isolable products together with tar matter, and, to our surprise, 2- and/or 3-cyano-6-nitroindoles are not detected at all. When the reaction is carried out in DMSO at 150°C, only demethoxylation occurred to give 83 (62%). On the other hand, utilizing KOt-Bu and p-chlorophenoxyacetonitrile (25), the vicarious substitution reaction (87ACR282) of 82 proceeds smoothly to give a 7-cyanomethylated indole (202, 67%) (2001H1151). 

Reaction of halo sulfonic acid esters with boranes 10-125 Alcoholysis of sulfonic acid derivatives 13-15 Vicarious substitution of aryl nitro compounds... 

Scheme 3.8 represents a typical ion-radical mechanism of the so-called vicarious nucleophilic substitution of hydrogen as it was described by the pioneering chemist M kocza (M kocza 1989) in his summarizing review. ESR studies of other heterocyclic systems in conditions of the hydrogen-to-nucleophile vicarious substitution were reported by the research group at the Siberian branch of the Russian Academy of Sciences (Donskaya et al. 2002, Vakul skaya et al. 2005, 2006, Titova et al. 2005). 

The vicarious substitutions of nitroarenes [22] involve nucleophiles which contain a leaving group X to enable elimination of HX from the a-adducts. As expected, the substitution is o-jp-to the nitro acceptor. 

Replacement of an aromatic fluorine atom by a carbon nucleophile is facilitated by the presence of electron-withdrawing groups [82] (equation 44) Replacement of an activated aryl hydrogen can occur in preference to a nonactivated aryl fluorine [S3] (equation 45) in reactions known as vicarious substitutions. 

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... 

Another kind of substitution of nitro compounds was Vicarious substitution (72 73) which takes place when the attack is carried out by a nucleophile... 

As base. For vicarious substitution of m-dinitrobenzene with carbon nucleophiles under photochemical conditions, TBAF serves as the base. The nitroaldol condensation with a-amino aldehydes constitutes the key step of a stereoselective synthesis of 1,3-diamino-2-alkanols. ... 

The initially formed adducts can be converted into products of nucleophilic substitution of hydrogen in a variety of ways oxidation with external oxidants, conversion into nitrosoarenes according to intramolecular redox stoichiometry, vicarious substitution, cine- and fe/e-elimination, ANRORC, etc. These processes have been discussed in a concise way in our preceding reviews [4,6-10]. The major message of those reviews is that nucleophilic substitution of hydrogen, in its many variants, is the main, primary process, whereas the conventional nucleophilic substitution of halogens X, the SnAt process, is just a secondary ipso reaction [9, 10]. 

Mechanisms of the nucleophilic substitution of hydrogen have been reviewed, and there has been a report of the synthesis of nitroaryl derivatives of glycine using the oxidative pathway. An example of the vicarious substitution mechanism is the formation of (13), a 3-styryl-substituted boron dipyrromethene, by reaction of a... 

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