Tandem [8 + 2] Cycloaddition−[2 + 6 + 2] Dehydrogenation Reactions Involving Imidazo[1,2-a]pyridines and Imidazo[1,2-a]pyrimidines

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• 作者：Maialen Aginagalde ; Yosu Vara ; Ana Arrieta ; Ronen Zangi ; Vicente L. Cebolla ; Arantzazu Delgado-Camn ; Fernando P. Cosso
• 刊名：Journal of Organic Chemistry
• 出版年：2010
• 出版时间：May 7, 2010
• 年：2010
• 卷：75
• 期：9
• 页码：2776-2784
• 全文大小：1183K
• 年卷期：v.75,no.9(May 7, 2010)
• ISSN：1520-6904

文摘

The reaction between benzynes and imidazo[1,2-a]pyridines (pyrimidines) to form benzo[a]imidazo[5,1,2-cd]indolizines and 2,3,9c-triazocyclopenta[j,k]fluorenes has been studied computationally and experimentally. It is found that these reactions take place via tandem [_π8_s + _π2_s] and [_σ2_s + _π6_s + _σ2_s] processes. The [8 + 2] cycloaddition steps are essentially barrierless, and the aromatization steps occur via highly synchronous aromatic transition structures. From an experimental standpoint, the reaction is feasible under microwave irradiation and using 2-(trimethylsilyl)phenyl triflates as benzyne precursors. Depending on the substitution pattern in the starting triflate a complete regiocontrol of the reaction can be achieved. The tetracyclic compounds thus prepared emitted blue light when excited at 365 nm and exhibited interesting photophysical properties.