Chromatographic-mass spectrometric study of the reaction of 1,2-diamino-4,5-diphenylimidazole with aromatic aldehydes and cyclohexane-1,3-diones
Abstract
This study presents a novel and efficient approach to the synthesis of fused tricyclic heterocyclic systems based on the reaction of 1,2-diamino-4,5-diphenylimidazole with 2-benzylidene-5,5-dimethylcyclohexane-1,3-dione. The aim of the research was to elucidate the mechanism of this transformation and to optimize reaction conditions using modern analytical techniques, specifically high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC/HRMS).
Based on the structural features and nucleophilic/electrophilic nature of the starting materials, several possible reaction products were proposed, including imidazopyrimidines, imidazotetrazines, and imidazocinolines. However, experimental data confirmed that the major pathway involves the formation of an imidazopyrimidine intermediate, followed by deamination and oxidative aromatization. The final stable compound obtained was the previously unreported 8,8-dimethyl-2,3,5-triphenyl-8,9-dihydroimidazo[2,1-b]quinazolin-6(7H)-one.
It was established that the highest conversion of reactants and yield of the target product (63%) were achieved by refluxing the reaction mixture in acetic acid for one hour. Alternative solvents such as methanol, DMF, isopropanol, and their mixtures resulted in lower selectivity and the formation of complex mixtures of by-products, as confirmed by TLC and HPLC/MS analysis.
HPLC/HRMS analysis, based on full ion current chromatograms, enabled the identification of starting compounds and key intermediates, including species consistent with tetrazane and imidazopyrimidine structures. The use of electrospray ionization (dual-ESI) on a TOF LC/MS system allowed for accurate mass determination and structural confirmation of the final product. Additional verification was performed using ¹H and ¹³C NMR spectroscopy and thin-layer chromatography (TLC) under UV detection.
The obtained results demonstrate the high selectivity and synthetic utility of this method. The proposed approach offers a convenient route to complex imidazoquinazoline scaffolds from readily available precursors. It may be applicable in the development of biologically active compounds, fluorescent sensors, and advanced functional materials.
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References
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