Heterocycles. 182. Neighboring group interaction in ortho-substituted heterocycles. 2. 1,2,4-Oxadiazolylpyridines and pyrido[2,3-d]pyrimidine 3-oxides

Polycyclic N‐Heterocyclic Compounds, Part 72: Reaction of N‐([1]Benzofuro (or Benzothieno)[3,2‐d]pyrimidin‐4‐yl)formamidine and N‐(Pyrido[2,3‐d]pyrimidin‐4‐yl)formamidine Derivatives with Hydroxylamine Hydrochloride

“…We speculated that fused electron‐deficient aromatics such as pyridine could affect this amide oxime stability. To test this, the requisite formamidine ( 12a ) [8] and acetamidine ( 12b ) starting materials were synthesized by the same method as described above from amine 11 (Scheme 3). We examined the reaction of 12a with 1.2 equiv of hydroxylamine hydrochloride in methanol at room temperature.…”

“…To a suspension of 4‐aminopyrido[2,3‐ d ]pyrimidine [8] ( 11 , 300 mg, 2.05 mmol) in dry toluene (30 mL), N , N ‐dimethylformamide dimethyl acetal (340 mg, 2.85 mmol) was added, and the mixture was refluxed for 3 h. The solution was evaporated in vacuo , and the residue was recrystallized from benzene to give 12a (286 mg, 69%) as a white granule, mp 162–164°C (lit. [8] 164–166°C); 1 H NMR (DMSO‐ d 6 ): δ 3.24 (s, 3H, NMe), 3.27 (s, 3H, NMe), 7.58 (dd, 1H, J = 8.2, 4.4 Hz, H6), 8.82 (s, 1H, NC H NMe 2 ), 8.83 (dd, 1H, J = 8.2, 2.0 Hz, H5), 8.98 (s, 1H, H‐2), 9.09 (dd, 1H, J = 4.4, 2.0 Hz, H7); FAB‐ms: m/z 202 (MH + ).…”

Oximes of five-membered heterocyclic compounds with three and four heteroatoms 1. Synthesis and structure (review)

“…1,2,4-Oxadiazole amidoximes 46 were successfully synthesized in this way from the amidines 45 [34]. The oxime 48 is formed in a similar way from the N,N-dimethylaminomethyleneamino derivative 47 and hydroxylamine hydrochloride in methanol [35]. .…”

Synthesis of 1,2,4-oxadiazoles (a review)

“…Versek et al [24] studied the conversions of O-acetamidoximopyridines (XXVII) and 1,2,4-oxadiazoles containing amino groups (XXVIII) into pyrido [2,3-d]pyrimidine N-oxides (XXIX) and estimated the stability of 1,2,4-oxadiazoles XXVIII with respect to hydrolysis. It was established that the latter 1,2,4-oxadiazoles converted into O-acylated amidoxime XXVII only in hot aqueous alkali solution.…”