Nucleophilic Substitution ofHydrogen in Nitroarenes: A New Chapter of Aromatic Chemistry

Basic concepts, mechanistic principles and the broad applicationof nucleophilic substitution of hydrogen in nitroarenes and otherelectron-deficient arenes in organic synthesis are presented in aconcise way. It was shown that the initial process between nucleophilesand (halo)nitroarenes is a fast and reversible addition - inpositions occupied by hydrogen - to form anionic σ H adductsthat can then be converted into products of nucleophilic substitutionof hydrogen in a few ways. Only when these pathways for rapid conversionof the σ H adducts into products of nucleophilicsubstitution of hydrogen are not available, do the σ H adductsdissociate. The subsequent slower formation of σ X adducts,followed by departure of X anions, results in the conventional nucleophilicaromatic sub-stitution of halogens, namely the S N Arreaction. Thus the S N Ar reaction is a secondary IPSO substitution, whereas nucleophilic substitutionof hydrogen is a primary fast process. It is therefore necessaryto introduce corrections in appropriate chapters of textbooks andmonographs. 1 Introduction 2 Oxidative Nucleophilic Substitution of Hydrogen (ONSH) 3 Vicarious Nucleophilic Substitution of Hydrogen (VNS) 4 Other Ways of Converting the σ H Adducts 5 Application of Nucleophilic Substitution of Hydrogen in OrganicSynthesis 5.1 Introduction of Carbon Substituents 5.2 Introduction of Heteroatom Substituents 5.3 Construction of Carbo- and Heterocyclic Rings 6 Concluding Discussion