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Stable anionic sigma-complexes of highly electrophilic aromatics and C-nucleophiles: synthesis and oxidation.
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1  N.D. Zelinsky Institute of Organic Chemistry RAS


Functionalization of arenes provides their chemical diversity and opens a way to valuable substances that are widely used in medicine, pharmaceutics, agriculture, energetic and other areas. In recent years, the functionalization of the CH bond has become an important tool for the implementation of such processes. Nucleophilic substitution of hydrogen (SNH) in arenes has acquired an intensive development as more prospective way of functionalization than classical SNAr processes occurring through ipso-substitution of a nucleofuge. Two general SNH processes are oxidative (ONSH) and vicarious (VNSH) nucleophilic substitution of hydrogen taking place through the generation of sн-adduct. In case of highly electrophilic substrates, the intermediate sigma-adducts can be isolated, identified and their chemical behavior can be studied.

In this work we studied the reactions of dinitrobenzoannulated heterocycles (furazan, thiadiazole, selenadiazole, pyridine) with anionic C-nucleophiles (mono- and diketones, nitroalkanes and related compounds). It was found that these reactions provided stable anionic adducts in high yield. Consecutive oxidation with ammonium cerium (IV) nitrate resulted in re-aromatization with formation of the corresponding substitution products, formally representing C-H-functionalized benzoheterocycles.

Thus, a series of the previously unknown dinitrobenzoazoles and azines with different pharmacophoric fragments in benzene ring were synthesized using sigma adducts as key intermediates of C-H functionalization of π-deficient nitroarenes.

Keywords: CH-functionalization; nitroarenes; carbon nucleophiles; nucleophlic addition; anionic sigma-complexes