Synthesis of 2-Pyridone Containing Heterocycles

Synthesis of 2-Pyridone Containing Heterocycles Using Conventional Heating... 

This chapter has taken the reader through a number of microwave-assisted methodologies to prepare and further functionalize 2-pyridone containing heterocycles. A survey of inter-, intramolecular-, and pericyclic reactions together with electrophilic, nucleophilic and transition metal mediated methodologies has been exemplified. Still, a number of methods remain to be advanced into microwave-assisted organic synthesis and we hope that the smorgasbord of reactions presented in this chapter will inspire to more successful research in this area. 

Vinamidinium salts are important intermediates in the synthesis of heterocycles. The 2-chloro-l,3-bis(dimethylamino)trimethinium hexafluorophosphate salt has been used in the preparation of the highly selective Cox-2 inhibitor etoricoxib (Scheme 1). This method describes a straight-forward preparation of the hexafluorophosphate salt which is a crystalline, thermally and shock-stable, non-hygroscopic solid. The submitters have extensively studied the preparation of vinamidinium salts and demonstrated that the method is applicable to substituted acetic acids that contain an electron-withdrawing group (Table 1)." The annulation reaction is also general and useful for the preparation of pyridines, pyridones and pyridine N-oxides. ... 

Nitrogen-containing heterocyclic enone systems also reacted with allene to give (2 + 2)-cycloadducts, as was shown in alkaloid synthesis.178 As the keystep in the synthesis of an annotinine derivative, allene was added to 157 and the adduct 158 was obtained in quantitative yield. Various uracils have been modified by photochemical (2 + 2)-cycloaddition with olefins, e.g., vinylene carbonate,17,18° vinyl ethers, vinyl acetates, and (cetene acetals yielded 159.181 Very recently the photochemical addition of cyanoethylenes to 2-pyridones has been observed to yield mixtures of tetrahydroazocin-2-ones (160) and (2 + 2)-cycloadducts (161).182... 

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