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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 Introduction2 Structure, Availability, and Reactivity of 2-Pyridones3 Monocyclic Piperidine Alkaloids from 2-Pyridones4 Polycyclic Alkaloids, Their Derivatives, and Alkaloid-Inspired Compounds from 2-Pyridones4.1 New Ring Formation Involving C/N Atoms of the 2-Pyridone Ring4.1.1 Indolizine-Fused 2-Pyridones: Camptothecins and Related Compounds4.1.2 Other Indolizines from 2-Pyridones4.1.3 Compounds Bearing the Quinolizine Ring System4.2 New Ring Formation Involving C/C Atoms of the 2-Pyridone Ring4.2.1 C-2/C-3 Ring Fusion4.2.2 C-3/C-4 Ring Fusion4.2.3 C-4/C-5 Ring Fusion4.2.4 C-5/C-6 Ring Fusion4.2.5 C-2/C-4 Ring Bridge4.2.6 C-2/C-6 Ring Bridge4.2.7 C-3/C-5 Ring Bridge4.2.8 C-3/C-6 Ring Bridge4.2.9 C-4/C-6 Ring Bridge5 Conclusion

A short and efficient synthesis for a series of 1,6-diaryl- 3,4-diarylaminohexa-2,4-diene-1,6-diones was developed. Based on the acylation-prototropism sequence during the reaction of vari- ous aryl methyl ketones with bis-imidoyl chlorides, the products were isolated in good yields. Substituted acetophenones, acetyl- thiophene, 3-acetylpyridine, and acetylferrocene can be integrated into this reaction as ketone component. Similarly, a-tetralone can be transformed with bis-electrophiles into the corresponding bis- enaminones. Treatment of 2-acetylpyridine with N,N¢-bis(4- tolyl)ethanebis(imidoyl) dichloride yielded not only the expected bis-enaminone, but also a new quinolizine derivative which was structurally characterized by single crystal X-ray analysis. Analo- gously, pinacolone and cyclopropyl methyl ketone can readily be converted into bis-enaminones. Monoimidoyl chlorides showed the same reactivity, providing derivatives in high yields.

Synthesis of some novel classes of quinolizine-, indolizine- and pyrido-1,4-oxazine-fused quinoline derivatives via a three-component reaction under solvent-free conditions by exploring the 'tertiary amine effect' reaction strategy.

4-Hetaryl and 4-tosyl-1,2,3,3a,4,5-hexahydropyrrolo[l,2-a]quinoline-4-carbonitriles were prepared in two steps by the condensation of 2-(l-pyrrolidinyl)benzaldehydes with substituted acetonitriles XCH 2 CN (X = hetaryl, tosyl), followed by the thermal cyclization of the corresponding arylidene derivatives. Similarly, starting from 2-(l-piperidinyl)benzaldehydes 5-hetaryl and 5-tosyl-2,3,4,4a,5,6-hexahydro-1H-pyrido[l,2-a]qumoline-5-carbonitriles were obtained. For the hetaryl-substituted derivatives the cyclization step was found to be assisted by protons. In addition 4,5,5a,6,7,8-hexahydro-1H-pyrazolo[3,4-e]indolizine and l,4,5,5a,6,7,8,9-octahydro-pyrazolo[4,3-c]quinolizine derivatives were prepared by the same method starting from 5-(1-pyrrolidinyl)-and 5-(1-piperidinyl)-3-methyl-l-phenylpyrazole-4-carbaldehydes. The relative configuration between the bridgehead hydrogen and the cyano group was assigned as trans on the basis of x-ray crystallographic data.