Synthesis and structural elucidation of pyrimido‐[1,2‐a]benzimidazoles and fused derivatives. i. dihydropyrimido[1,2‐a]benzimidazoles

Abstract

The condensation of 2‐benzimidazolarnine (4, BIA) with α,β‐unsaturated ketones 1 affords, according to Desenko, Orlov et al. [12,13], 1,4‐dihydropyrimido[1,2‐a]benzimidazoles (1,4‐DHPBI, 5I). However, the described ring closure reactions could a priori also yield isomeric 1,2‐DHPBI 8I or tautomers of DHPBIs 5I and 8I. An unequivocal proof for the postulated structures 5I was not presented. We prepared, as described [12,13], BIA‐chalcone‐ and BIA‐benzalacetone‐condensate X and Y, 5a, e or 8a, e, and additionally, their hydrochlorides. One and two dimensional high resolution nmr analyses showed that only isomers 5a, e and salts 5a, e·HCl were generated. In DMSO‐d6 these isomers exclusively exist as 1,4‐dihydro tautomers 5a, eI and 5a,eI·HCl. In trifluoroacetic acid 3,4‐dihydro tautomers 5a, eIII·CF3COOH besides of tautomers 5a, eI·CF3COOH (≈︁1:4) were ascertained. Action of ethanolic hydrochloric acid on base 5eI afforded, besides of 5eI·HCl as main product, a small amount of 2‐methyl‐4‐phenyltetrahydropyrim‐ido[1,2‐a]benzimidazol‐2‐ol hydrochloride 9e·HCl. The reaction of BIA 4 with α,β‐unsaturated ketones 1b‐d and f yielded 1,4‐DHPBI 5b‐dI and 5fI and their hydrochlorides, respectively. The stereochemistry of bases 5a, eI, of salts 5a‐eI·HCl and 5a, eIII·CF3COOH, and of addition product 9e·HCl was elucidated by nmr (stereoformulae in Figures 1–3 and Scheme 5). The accomplished nmr‐analyses are documented in detail and discussed.

Comparative studies on conventional and microwave-assisted synthesis of a series of 2,4-di and 2,3,4-trisubstituted benzimidazo[1,2-a] pyrimidines and their antimicrobial activities

“…Approaches for the synthesis of benzimidazo[1,2-a] pyrimidine derivatives generally involve using harsh dehydrating reaction conditions [8,[25][26][27][28][29][30]. These reactions are often carried out under high pressure and require long reaction time.…”

Addition of hydrazine to 4,7‐dihydro[1,2,4]triazolo[1,5‐a]pyrimidines: Hydrazine derivatives of 4,5,6,7‐tetrahydro[1,2,4]triazolo[1,5‐a]pyrimidine

“…The reaction mixture was cooled to 20 C, mixed with benzene (20 mL) and the precipitate formed was collected by filtration and crystallized from DMF-methanol mixture. ,4.31% H,27.22% N. Found: 55.92% C,4.24% H,5,6,2,4]triazolo[1,5-a] pyrimidin-5-yl)hydrazine (2a) and 2-(3-hydrazono-1-phenylbutyl)[1,2,4]triazol-3-amine (3a). A solution of 1a [7] (1.40 g, 6.6 mmol) and 85% hydrazine hydrate (1.66 g, 30 mmol) in dioxane (7 mL) was heated for 60 min and the solvent was evaporated under reduced pressure.…”

“…Only several adducts of dihydroazolopyrimidines (namely hydrates) are described; they were formed either by attempt of preparation of corresponding dihydroazolopyrimidine [5], or directly from previously prepared dihydroazolopyrimidine in attempts of its salt formation with HCl (as side product without isolation) [6].…”

Spectral characterization and biological studies of some ternary complexes with molecular docking investigations against MERS and SARS type coronaviruses

“…The antibacterial activity of these studied compounds was investigated by using agar well method [24,25] against B. subtilis and E. coli. The test solution (3×10 -3 M) was prepared in DMSO.…”