Hydroxypyridines amination, nucleophilic

Other interesting data in these reactions concern the H/D isotopic effect of the nucleophile/catalyst, for example when [2-hydroxypyridine] = [2 — 02H] = 0.08, fcobsH/ obsD = 1-5. Since a very poor H/D effect is usual in SjvAr reactions with neutral nucleophiles (amines) in apolar solvents10, the authors conclude that the unusually high H/D effect should be due to a difference in the Xh/Xd = 1.75 of the molecular complex. Nevertheless, the same effect could be explained on the basis of an autoassociation of... 

The reaction of furans with ammonia and its derivatives is of considerable synthetic utility (B-73MI31 too). Substituted furan-2-carbaldehydes and 2-acylfurans on heating with ammonia and ammonium salts, often under pressure, yield 3-hydroxypyridines. The mechanism of this reaction is thought to involve nucleophilic attack of ammonia at the 2-position. Ring opening affords an amino aldehyde or ketone and thence, by reclosure, the 3-hydroxy-pyridine (Scheme 29). A wide range of substitutents is tolerated. Primary amines with furan-2-carbaldehydes yield A-substituted pyrroles, the closure of the intermediate... 

Alternative methods include deprotonation of the amine, to enhance its nucleophilicity, by one equivalent of sodium methoxide, sodium amide, metallic sodium,n-butyllithium, sodium hydride in dimethyl sulfoxide or Grignard reagent. Under less drastic basic conditions 2-hydroxypyridine catalyzes the reaction at elevated temperatures (130-170 °C). ... 

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... 

---