ChemInform Abstract: UNTERSUCHUNG DER STRUKTURELLEN ANFORDERUNGEN AN EINE DIMROTH‐UMLAGERUNG BEI POLYAZAINDOLIZINEN

Abstract

Aus dem Imidazo(l ,2‐a)pyrimidinen (I) erhält man beim Erhitzen mit Alkali über eine in ihrem Ablauf ausführlich untersuchte Umlagerung die Isomeren (II), wobei sich z.Tl. Gleichgewichte zwischen den beiden Isomeren (I) und (II) einstellen.

Synthesis of pyrazolo[1,5‐a]‐, 1,2,4‐triazolo[1,5‐a]‐ and imidazo[1,2‐a]pyrimidines related to zaleplon, a new drug for the treatment of insomnia

“…The structure of these compounds was confirmed by chemical shifts and protonproton coupling constant values which are consistent with those reported in the literature for analogues 7-arylsubstituted imidazo[1,2-a]pyrimidines [9,12]. In fact, the 1 H-nmr spectrum of 3a, showed for pyrimidine ring protons two doublets at 8.50 and 7.36 ppm (δ), whose coupling constant J = 7.0 Hz has been described as characteristic for the H-5 -H-6 sequence.…”

Studies directed toward a total synthesis of nucleoside Q. Annulation of 2,6-diaminopyrimidin-4-one with .alpha.-halo carbonyls to form pyrrolo[2,3-d]pyrimidines and furo[2,3-d]pyrimidines

“…16-18•27 For several reactions where aminopyrimidines annulate from nitrogen to nitrogen to form a fused imidazole ring, the carbonyl of the -halo carbonyl becomes bonded to the exocyclic amino and the halogen-containing carbon to a ring nitrogen. [28][29][30][31] In a recent study kinetic evidence is presented to indicate that initial reaction occurs between the 6-amino of adenosine 5'monophosphate and the carbonyl carbon of chloroacetaldehyde, followed by cyclization and loss of water.32 Condensations involving d-dicarbonyls and aminopyrimidines, however, have been suggested to involve initial acylation at C-5 of the pyrimidine followed by ring closure. 33 The mechanisms leading to 5 and 6 must involve at least three major steps (not necessarily in this order): (1) bond formation between a heteroatom (0 or N) of 3 and a carbon of the a-halo ketone, (2) bond formation between C-5 of 3 and a carbon of the -halo ketone, and (3) loss of water.…”

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

“…The imidazodiazines are as follows in the sequence of insertion of this additional nitrogen atom in a clockwise sense: imidazo [1,5-b]pyridazine (219) (224), [161] imidazo [1,5-d] [1,2,4]triazine (225), [162] imidazo[1,5-a]-1,3,5-triazine (226), [163] and imidazo [5,1-c] [1,2,4]triazine (227) [164,165] } have also been described, most of these ring systems have been synthesized via ring closure of the six-membered ring and, hence, these syntheses are discussed in Science of Synthesis, Vol. [167] The available literature on these ring systems is rather sparse: some NMR studies, [168,169] X-ray investigations, [170] and theoretical calculations [171] have been reported. As concluded from studies on the acidity constants of ring systems 219 and 221, these compounds undergo protonation on the imidazole nitrogen atom; [166] similarly, quaternizations also take place at this site of the molecules.…”

“…Thus, chlorination with N-chlorosuccinimide yields the 1-chloro-3-methyl derivative 244, [179] bromination affords the analogous 1-bromo compound 245 [179] (a similar regioselectivity with bromination of the related imidazo[1,5-b][1,2,4]triazines 224 has also been reported [161] ) and, similarly, the Mannich reaction [179] results in formation of the 1-dimethylamino derivative 246. [167] Scheme 45 Electrophilic Substitutions on Imidazo[1,5-a]pyrazines and Imidazo[1,5-a]pyrimidines [167,179] Nucleophilic substitution of halogen atoms has proved to be a general tool for introducing desired new substituents into the heterocyclic systems. [173] Bromination of the unsubstituted related ring system imidazo[1,5-a]pyrimidine (222) when carried out with N-bromosuccinimide leads, in turn, to a dibromo product 247.…”