|標題:||Regioselective, Unconventional Pictet-Spengler Cyclization Strategy Toward the Synthesis of Benzimidazole-Linked Imidazoquinoxalines on a Soluble Polymer Support|
Yellol, Gorakh S.
Department of Applied Chemistry
|關鍵字:||diversity-oriented synthesis;heterocycles;microwave chemistry;Pictet-Spengler cyclization;solid-phase synthesis|
|摘要:||A novel strategy for an unconventional Pictet-Spengler reaction has been developed for the regioselective cyclization of the imidazole ring system at the C2 position. The developed strategy was utilized to develop a diversity-oriented parallel synthesis for bis(heterocyclic) skeletal novel analogs of benzimidazole-linked imidazoquinoxalines on a soluble polymer support under microwave conditions. Condensation of polymer-immobilized o-phenylenediamines with 4-fluoro-3-nitrobenzoic acid followed by nucleophilic aromatic substitution with an imidazole motif affords bis(heterocyclic) skeletal precursors for the Pictet-Spengler reaction. The unconventional Pictet-Spengler cyclization with various aldehydes was achieved regioselectively at the C2 position of the imidazole ring to furnish rare imidazole-fused quinoxaline skeletons. During the Pictet-Spengler cyclization, aldehydes bearing electron-donating groups afford 4,5-dihydro-imidazoquinoxalines, which then auto-aromatize into benzimidazole-linked imidazo[1,2-a]quinoxalines. However, interestingly, aldehydes bearing electron-withdrawing groups directly provide aromatized imidazo[1,2-a]quinoxalines, which unexpectedly afford novel benzimidazole-linked 4-methoxy-4,5-dihydro-imidazo[1,2-a] quinoxalines after polymer cleavage.|
|期刊:||CHEMISTRY-AN ASIAN JOURNAL|