Title: | Regioselective, Unconventional Pictet-Spengler Cyclization Strategy Toward the Synthesis of Benzimidazole-Linked Imidazoquinoxalines on a Soluble Polymer Support |
Authors: | Chen, Chih-Hau Kuo, Jaren Yellol, Gorakh S. Sun, Chung-Ming 應用化學系 Department of Applied Chemistry |
Keywords: | diversity-oriented synthesis;heterocycles;microwave chemistry;Pictet-Spengler cyclization;solid-phase synthesis |
Issue Date: | 6-Jun-2011 |
Abstract: | 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. |
URI: | http://dx.doi.org/10.1002/asia.201000913 http://hdl.handle.net/11536/22758 |
ISSN: | 1861-4728 |
DOI: | 10.1002/asia.201000913 |
Journal: | CHEMISTRY-AN ASIAN JOURNAL |
Volume: | 6 |
Issue: | 6 |
Begin Page: | 1557 |
End Page: | 1565 |
Appears in Collections: | Articles |
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