2-Pyridone ring 5,6-dihydro-5-hydroxy

Pyridone ring, 2,3-dihydro-, N-condensed 21, 820 2-Pyridone ring, 4-hydroxy ... 

Pyridone ring. A mixture of 2-methoxy-zli-pyrroline, dimethyl acetonedicarbox-ylate, and triethylamine allowed to stand 6 days -> methyl l,2-dihydro-7-hydroxy-5-keto-3H,5H-indolizine-8-carboxylate. Y 66%. F. e. s. S. Rajappa, B. G. Advani, and R. Sreenivasan, Indian J. Chem. JO, 323 (1972). 

Pyridone from 5-hydroxy-5,6-dihydro-2-pyridone ring... 

The importance of ring size holds also for tautomerism of -pyrrol-5-ones and. d -dihydro-6-pyridones. While the former compounds behave as cyclic 1-methyl-2-alkyl-2-hydroxy-5-pyrrolidones 179) (76) [or, on distillation, as the dehydrated l-methyl-2-alkyl-J -pyrrolones (77)], the latter compounds exist as acyclic N-methylamides of 8-oxo-acids (78) [as shown by infrared spectroscopy (/80)j. The dehydration of 78 during distillation to form l-methyl-2-alkyl-. -dihydro-6-pyridones (79) is achieved only with difficulty. 

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