Pyridones – Powerful Precursors for the Synthesis of Alkaloids, Their Derivatives, and Alkaloid-Inspired Compounds.

2-Pyridone is characterized by a very wide range of reactivity of a different nature, ranging from electrophilic aromatic substitution, CH–metal-mediated reactions, and NH/OH functionalization of both possible lactam/lactim tautomers, through cycloaddition, to nucleophilic addition and transformation of the tautomeric C=O/C–OH moiety. The high availability of 2-pyridones and the possibility of their far-reaching functionalization additionally increased their values. Therefore, they are very useful building blocks for the synthesis of structurally diverse piperidine and pyridine compounds, including naturally occurring 2-pyridones. This review reports on the use of simple 2-pyridones in the synthesis of alkaloids and alkaloids-inspired compounds based on the piperidine or pyridine framework. 1 Introduction 2 Structure, Availability, and Reactivity of 2-Pyridones 3 Monocyclic Piperidine Alkaloids from 2-Pyridones 4 Polycyclic Alkaloids, Their Derivatives, and Alkaloid-Inspired Compounds from 2-Pyridones 4.1 New Ring Formation Involving C/N Atoms of the 2-Pyridone Ring 4.1.1 Indolizine-Fused 2-Pyridones: Camptothecins and Related Compounds 4.1.2 Other Indolizines from 2-Pyridones 4.1.3 Compounds Bearing the Quinolizine Ring System 4.2 New Ring Formation Involving C/C Atoms of the 2-Pyridone Ring 4.2.1 C-2/C-3 Ring Fusion 4.2.2 C-3/C-4 Ring Fusion 4.2.3 C-4/C-5 Ring Fusion 4.2.4 C-5/C-6 Ring Fusion 4.2.5 C-2/C-4 Ring Bridge 4.2.6 C-2/C-6 Ring Bridge 4.2.7 C-3/C-5 Ring Bridge 4.2.8 C-3/C-6 Ring Bridge 4.2.9 C-4/C-6 Ring Bridge 5 Conclusion [ABSTRACT FROM AUTHOR]