Pyridinols

Oxygen Substituents. The presence of oxygen or sulfur attached to the ring can affect the chemistry of those compounds through tautomerism. This phenomenon ia the pyridine series has been well studied and reviewed (38). An example of 2-pyridone—2-pyridinol tautomerism was shown ia equation 2, compound (16). 

The compounds 2- (16) and 4-pyridone (38) undergo chlorination with phosphoms oxychloride however, 3-pyridinol (39) is not chlotinated similarly. The product from (38) is 4-chloropyridine [626-61-9]. The 2- (16) and 4-oxo (38) isomers behave like the keto form of the keto—enol tautomers, whereas the 3-oxo (39) isomer is largely phenolic-like, and fails to be chlotinated (38). 

Ethyl-2-methylpyridine (7) is used as starting material for niacin (27). 2,6-Dimethylpyridine (5) is used for the antiarteriosclerotic pyridinol... 

Similar results were reported earlier for 164 the pyridoiie 164a is the major tautomer in polar solvents, while the pyridinol 164b predominates in nonpolar ones (67AC877). Tire hydroxy form can be stabilized by intramolecular hydrogen bonding [71JCS(B)2339],... 

Pyridinol carbamate 160 ,170 -Dihyd roxy progesterone Algestone acetophenide L-Diiodo thyronine Liothyronine p-Diisobutylphenol... 

Irradiation of the unsymmetrically substituted 2,3,4,6-tetraphenylpyridine 1-oxide (5) under these conditions gives 2,4,6,7-tetraphenyl-l, 3-oxazepine (7) in 30 % yield, together with 2,4,5,6-tetraphenylpyridin-3-ol (10) in 37% yield and 2,3,4,6-tetraphenylpyridine (30%).11 It has been suggested that the reaction proceeds by way of the oxaziridines 6 (which yields 7) and 8 (which yields the isomeric oxazepine 9) the latter rearranges to the pyridinol 10. 

Ru(6-methyl-2-pyridinolate)2(PPh3)2, 2,795 4, 466 RuC48H44C12P4 RuCl2(PHPh2)4,4, 378 RuC4sH44N03P 2... 

Me2NCHO, warm then substrate slowly, reflux, 3 h 83%) the same substrate (219) with 2-amino-3-pyridinol (220, X = N) gave 12//-pyrido-[2, 3 5,6]oxazino[2,3-/7]quinoxaline (221, X = N) (likewise 72%) " and analogs were made somewhat similarly. ... 

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