Pyridone 5,6-dihydro-5-hydroxy

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. 

Methylquinoline (2) 3-methyl-2(lH)quinolinone (3) 5,6-dihydro-5,6-dihydroxy-3-me thy 1-2(1 H)quinolinone (4) 6-hydroxy-3 -methyl-2( 1 H)quinolinone (5) 5,6-dihydroxy-3-methyl-2(lH)quinolinone (6) 3-methyl-2,4,6-trihydroxypyridine (1) 4-Methylquinoline (2) 4-methyl-2(lH)quinolinone (3) 7,8-dihydro-7,8-dihydroxy-4-methy 1-2(1 H) quinolinone (4) 8-hydroxy-4-methyl-2(lH)quinolinone (5) 7,8-dihydroxy-4-methyl-2(1 H)quinolinone (6) 6-hydroxy-5-(2-carboxyethenyl)-4-methyl-2( 1 H)pyridone... 

In a departure from the biomimetic catecholamide-based siderophores, Raymond s group have turned to derivatives of l-hydroxy-2(I//)-pyridone a structure which can be regarded as a cyclic hydroxamic acid264. Unlike hydroxamate siderophores, l,5-bis[l,2-dihydro-l-hydroxy-2-oxo-pyridin-6-yl)carbonyl]-l,5-diazaheptane (33) rapidly removes iron from transferrin. 

Although the mechanism of chlorination of pyridine A-oxides by the action of phosphorus oxychloride, phosphorus pentachloride, or sulfuryl chloride has not been established, it seems most likely that some of these reactions involve intra- or inter-molecular attack by chloride ion or potential chloride ion following complexing at oxygen (see Sections II and IV). With a few exceptions, they are therefore more appropriately discussed under the heading of nucleophilic substitutions (Section IV, A, 3). One such exception may be the reaction of A-hydroxy-4-pyridone with sulfuryl chloride, which ultimately gives l,2,2,3,3,5,6-heptachloro-2,3-dihydro-4-pyridone (65). It has been proposed that the first step in this reaction is the formation of 3,5-dichIoro-AT-hydroxy-4-pyridone.157 If this is so, then it must involve electrophilic attack at the two /3-positions, followed by the more usual nucleophilic substitutions. 

The reaction of ethyl acetoacetate with cyclopentanone in the presence of excess ammonium acetate gives 2-hydroxy-4-methyl-6,7-dihydro-5/7-1-pyr incline (127) in 23.5% yield.20,86 The spectral evidence available is not conclusive, but by anology with simpler systems, it seems certain that the pyridone form (127b) is predominant. 

A -Alkylpyridinium ions add hydroxide ions reversibly and exclusively in the 2-position, forming 2-hydroxy-l,2-dihydro-iV-alkylpyridines ( pseudobases , e.g. 43) which can be oxidized by mild oxidizing agents to A-alkyl-2-pyridones, e.g. 44 ... 

To a solution of 100 mg (2R)-2-((lR)-hydroxy-l-hept-3-yn-2-one)-l-[((15, 2R)-2-(1-methyl- 1-phenylethyl) cyclohexyoxy) carbonyl]-5-(triisopropylsilyl)-2,3-ciihydro-4-pyridone (0.161 mmol) in 7 mL methanol was added 66 mg cerium(III) chloride heptahydrate (CeCl3 7H20, 0.177 mmol) in one portion. After being stirred for 10 min, the mixture was cooled to —50°C, and 9 mg sodium borohydride (0.241 mmol) was added. The reaction mixture was stirred for an additional 10 min, quenched with 10 mL water, and extracted with CH2CI2 (3 x 10 mL). The combined extracts were dried over MgS04 and concentrated under reduced pressure. The residue was purified by radial PLC (silica gel, 30% EtOAc/hexanes) to give 96 mg (2R)-2-((lR,25)-dihydroxy-hept-3-yne)- -[((15,2R)-2-( 1-methyl- 1-phenylethyl)-cyclohexyloxy)carbonyl]-5-(triisopropylsilyl)-2,3-dihydro-4-pyridone as a colorless oil, in a yield of 96%. 

Tetra-n-butylammonium hydroxide 3-Hydroxy-2,3-dihydro-4-pyridones s. 44, 435... 

Chloro ulfonyl isocyanate and isoprene in ether give 5-hydroxy-3-methyl-2-pentenoic acid lactone (4-methyl-5,6-dihydro-2-pyrone, XII-98) and 5-amino-3-methyl-3-pentenoic acid lactam (4-methyl-3,6-dihydro-2-pyridone, XII-99) by hydrolysis of intermediate N-sulfochlorides that were not isolated ... 

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... 

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

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