Browsing by Author "Kuo, Jaren"

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Enantioselective Synthesis of Benzimidazolyl Quinoxalinones on Soluble Polymer Support Using Focused Microwave Irradiation
(2009-03-01)
Chanda, Kaushik
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Kuo, Jaren
;
Chen, Chih-Hau
;
Sun, Chung-Ming
;
應用化學系
Focused microwave irradiation has been applied to a multistep synthetic sequence of reactions designed to generate benzimidazolyl quinoxalinones using a soluble polymer support. They were obtained by the ipso-fluoro (S(N)Ar) displacement of the immobilized ortho-nitro fluoro benzimidazoles with chiral alpha amino esters under microwave irradiation. Intermediate chiral organic-polymer conjugates when subjected to neutral reduction underwent a spontaneous intramolecular ring closure. Cleavage of the polymer support, at room temperature, did not cause any significant racemization resulting in the generation of a chiral molecular library with two points of structural diversity.
Regioselective, Unconventional Pictet-Spengler Cyclization Strategy Toward the Synthesis of Benzimidazole-Linked Imidazoquinoxalines on a Soluble Polymer Support
(2011-06-06)
Chen, Chih-Hau
;
Kuo, Jaren
;
Yellol, Gorakh S.
;
Sun, Chung-Ming
;
應用化學系
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.