Recent Developments in Transition-Metal-Free Functionalization and Derivatization Reactions of Pyridines

Pyridine is an important structural motif that is prevalent in natural products, drugs, and materials. Methods that functionalize and derivatize pyridines have gained significant attention. Recently, a large number of transition-metal-free reactions have been developed. In this review, we provide a brief summary of recent advances in transition-metal-free functionalization and derivatization reactions of pyridines, categorized according to their reaction modes. 1 Introduction 2 Metalated Pyridines as Nucleophiles 2.1 Deprotonation 2.2 Halogen–Metal exchange 3 Activated Pyridines as Electrophiles 3.1 Asymmetric 2-Allylation by Chiral Phosphite Catalysis 3.2 Activation of Pyridines by a Bifunctional Activating Group 3.3 Alkylation of Pyridines by 1,2-Migration 3.4 Alkylation of Pyridines by [3+2] Addition 3.5 Pyridine Derivatization by Catalytic In Situ Activation Strategies 3.6 Reactions via Heterocyclic Phosphonium Salts 4 Radical Reactions for Pyridine Functionalization 4.1 Pyridine Functionalization through Radical Addition Reactions 4.2 Pyridine Functionalization through Radical–Radical Coupling Reactions 5 Derivatization of Pyridines through the Formation of Meisenheimer-Type Pyridyl Anions 6 Conclusion