烯基自由基與矽基酮進行自由基連繼性環化反應的研究

Abstract

本實驗室之前針對矽基酮與烯基自由基環化反應的研究，顯示出此類化合物具有開發連繼性環化反應的可能。烯基自由基環化後所得到β-矽基烷氧自由基，經過Brook重排，產生因共振而穩定的烯丙基自由基。此系統最特殊的地方在於雙鍵的存在，自由基中間體可以透過共振使得三號碳的位置上具有自由基性質。我們利用這種特性，希望將此形式的反應發展為連繼性環化反應。 我們的構想是利用炔基做為自由基受體，利用三號碳所具有的自由基性質，進行第二次環化反應，架構出雙環化合物。本文設計出兩種類型的環化前驅物進行研究。

According to previous research in our laboratory, cyclizations of acylsilanes with vinyl radicals have been studied. This process involved intramolecular free radical cyclizations of a vinyl radical to the carbonyl group of acylsilane to give a β-silyl alkoxy radical. This radical then undergoes a radical Brook rearrangement to afford an α-silyloxy radical. Due to the presence of the vinyl group, this α-silyloxy radical is also an allylic radical. Finally, hydrogen abstraction occurs at the γ-position of this allylic system to give an enol silyl ether. Generally, 1,5-exo-cyclizations are more efficient than 1,6-exo-cyclizations. In this research we exploited this system further in the context of tandem radical cyclizations. We have constructed two systems in which the intermediate allylic radicals are trapped intramolecularly at the γ-position by radicalphilic groups. Specifically, we have synthesized acylsilanes with vinyl iodide tethered to an alkynyl functional group. The scope and limitations of this type of tandem cyclizations were studied.