An investigation of the minimal structural conditions lor the dirnroth‐type rearrangement in the polyazaindolizine series

Abstract

In the imidazo[1,2]diazine series, only the imidazo[1,2‐a]‐ and [1,2‐c] pyrimidine systems were found to undergo a Dimroth‐type rearrangement under basic aqueous conditions. The electronic and steric factors influencing the rearrangement rates of methyl substituted imidazo‐[1,2‐a] pyrimidines are discussed.

Synthesis of [1,2,4]triazoloquinazolinones and imidazoquinazolinones

“…An attempt to prepare l-phenyl [1,2,4]triazolo [4,3-u]quinazolin-5-one by reacting l a with benzoyl chloride in dimethylformamide and then refluxing the supposed benzhydrazide suspension yielded a product with no additional aryl protons in its pmr spectrum. Also, there appeared to be only one lowfield multiplet in contrast to the two found in the spectrum of 2a (Table 1).…”

“…On the basis of its pmr spectrum it was concluded that the product was the isomeric [1,2,4]triazolo[5,1-b]quinazolin-9-one (6a) formed by a Dimroth-type rearrangement well known in polyazaindolizines [2,3]. It was also found that 3a could be converted into this new product by treatment with hot aqueous sodium hydroxide.…”

“…It was also found that 3a could be converted into this new product by treatment with hot aqueous sodium hydroxide. Compound 6a is obtained, however, from alkaline treatment of 1,5-diamino-lH- [ 1,2,4]triazolo- [ 1,5-~]quinazolinium cation and by cyclisation of 2,3diamino-4-quinazolinone with triethyl orthoformate [6]. The up-field shift of the triazole proton is as expected from that observed in triazolopyrimidinones [4] where the carbonyl group no longer exerts its deshielding effect.…”

Product Class 5: Azaindolizines with Two Nitrogen Atoms in the Five-Membered Ring

“…Scheme 29 Reduction of Imidazo[1,2-b]pyridazine and Imidazo[1,2-a]pyrimidine Derivatives [25,136] [83,119] As the whole reaction sequence includes equilibria, these rearrangements are mostly run under thermodynamic control. The unsubstituted imidazo[1,5-a]pyridine (2), first synthesized [137] in 1955, is a stable lowmelting crystalline compound.…”

Structure du chloro-3 méthyl-2 4H-pyrazino[1,2-a]pyrimidinone-4

“…Compos6 pr6par~ par condensation du chloro-2 acetylacetate d'6thyle (Sablayrolles et al, 1984) sans r6arrangement de type DIMROTH (Guerret, Jacquier & Maury, 1971). Cristaux jaunes, stables ~ l'air, p.f.…”