Nucleophilic Substitutions of Nitroarenes and Pyridines: New Insight and New Applications

At the beginning of this article an in-depth comparison of electrophilic and nucleophilic aromatic and heterocyclic substitution processes examines their scopes of applicability in a new light. In the subsequent parts, recent progress in the area of halide and hydride displacement from pyridines is highlighted. Particular attention is paid to the leaving group aptitudes of fluoride and chloride, to the effect of 'passive' substituents on the reaction rates, and to the control of the relative reactivity at halogen-bearing 4-versus 2-(or 6-)positions. 1 Introduction 2 Electrophilic as Opposed to Nucleophilic Substitutions 3 Nitroarenes as Substrates for Nucleophilic Substitutions 4 Nucleophilic Substitution at Resonance-Disabled Positions 5 Nucleofugality Contest between Fluorine and Chlorine 6 Substituent Effects on the Reactivity of 2-Halopyridines 7 'Silyl Trick': Discriminating between Two Potential Exchange Sites 8 Hydride as the Nucleofugal Leaving Group 9 Summing Up