3- Methoxycarbonyl-2-hydroxypyridine

P-Hydroxy esters. Regioselective ring opening and homologation (methoxycarbonylation) of epoxides are achieved on treatment with Co2(CO)g and 3-hydroxypyridine. 

The dimethylamino group in diethyl (2 R=Et) and dimethyl 1-dimethylamino-3-oxobut-l-ene-2,4-dicarboxylates (2 R=Me) can be exchanged very easily with nitrogen nucleophiles. With primary amines in methanol or ethanol under reflux for several hours, substitution of the dimethylamino group by an amine takes place followed by intramolecular nucleophilic attack of the amino group on the ester to afford 1-substituted 5-alkoxycarbonyl-4-hydroxypyridin-2(lH)-ones 56 in 16-93% yields (5cheme 21). In the reaction of 56 with methyl (Z)-2-benzoylamino-3-dimethylaminopropenoate (57), first the intermediate 58 was formed, which cyclized into 6-substituted 3-benzoylamino-8-ethoxycarbonyl-2H,5H-pyrido[4,3-li]pyran-2,5-diones (59). However, with 3-dimethyla-mino-2-(methoxycarbonyl)propenoate (60) intermediate 61 is formed... 

The conversion of pyridine 1-oxide into 2-acetoxypyridine (or into 2-hydroxypyridine by hydrolysis of this ester) by reaction with hot acetic anhydride is a valuable reaction " Benzoic anhydride produces a similar result, but acetic anhydride has naturally been used more often, and the reaction has been applied to several pyridine l-oxides 8, 863 When a halogen, hydroxyl, methoxycarbonyl or nitro group is present at C(3), hydroxylation occurs mainly at C(2) rather than C(6), whilst a methyl group directs substitution about equally to each position. With nicotinic acid... 

Electron-attracting substituents should assist this reaction. However, with acetic anhydride in acetonitrile, 2-picolinic acid 1-oxide gives mainly pyridine 1-oxide and carbon dioxide, whilst the same reaction carried out under ultra-violet irradiation proceeds similarly but with the formation of a little more 2-hydroxypyridine. The methyl esters of the pyridine-carboxylic acid 1-oxides behave normally, but there is no evidence that the methoxycarbonyl group promotes the reaction, and 2-cyanopyridine 1-oxide does not react with acetic anhydride . The results of a kinetic study of the rearrangement of pyridine 1-oxide in acetic anhydride exclude the intramolecular rearrangement of the free cation (113) and also a free radical process. There remain the two possibilities of nucleophilic substitution by reaction between... 

---