a-錫基自由基加成到羰基與亞胺系統的分子內自由基環化反應研究

The Study of Intramolecular Free Radical Cyclizations of a-Stannanyl Radicals to Carbonyl and Imine System

翁紹華(Shau-Hua Ueng)

指導教授 ： 蔡蘊明

國立臺灣大學/理學院/化學研究所/博士(2004年)

https://doi.org/10.6342/NTU.2004.01436

摘要

a-錫基自由基加成到羰基進行分子內自由基環化反應，會經過一個有趣的 1,3-錫轉移機制。根據我們對於反應機制的研究， 1,3-錫轉移為一不可逆反應。另外我們在醛基 a 位加入雙甲基取代後，其競爭性環化反應會經由開環重排反應而得到環己基醛化合物 115 ，以及衍生物 120 、 121 。在反應系統中加入路易士酸時，在競爭性環化反應當中 a-錫基自由基加成到羰基的效率，由原本 a-錫基自由基加成到羰基與碳-碳雙鍵的比例為 0.70 增加為 1.22 。在 a-錫基自由基加成到醛基形成六員環的系統中，我們在醛基的 a 位上加入碸基來抑制 1,5-氫轉移並提升環合產物之產率，在這個系統中，我們得到了 41 % 的環合產物。根據氘化實驗，直接還原的產物中有一半是經由 1,5-氫轉移而來，而在w-錫基溴己醛的系統則全部經由 1,5-氫轉移而來。
有關 a-錫基自由基加成到亞胺系統，在腙與 oxime ether 的例子中，可以得到不錯的環合產率，但沒有看到 1,3-錫轉移的現象。在合成與純化亞胺 190 、 191 都面臨困難，而進行自由基環合反應之後也只得到雜亂的產物。 a-錫基黃酸酯與 a-錫基溴官能基在合成苯亞胺的系統中往往被破壞。

關鍵字

a-錫基自由基 ； 羰基 ； 亞胺 ； 環化反應

並列摘要

The mechanism of intramolecular free radical cyclizations of a-stannyl radicals to carbonyl involves an interesting 1,3-stannyl shift. According to our mechanistic study, 1,3-stannyl shift is an irreversible reaction. Competitive cyclization of a,a-dimethylaldehyde system undergoes ring opening rearrangement to give cyclohexylaldehyde 115 and related derivatives 120 、 121. After addition of Lewis acids in the reaction system, the efficiency of competitive cyclization of a-stannyl radical to carbonyl was improved. The ratio of a-stannyl radical addition to carbonyl and carbon-carbon double bond increased from 0.70 to 1.22. In the reaction of a-stannyl radical addition to carbonyl to form six-membered ring, we constructed a sulfonyl group at the a position of the formyl group to inhibit 1,5-H shift in order to increase the cyclization product yield. We obtained 41 % yield of the cyclization product in this system. According to the deuterium experiment, half of the straight reduction product of the a-sulfonylaldehyde was derived from a 1,5-H shift followed by hydrogen abstraction. In contrast, in the w-bromostannylhexanal system all the reduction product was obtained through a 1,5-H shift first.
In the case of a-stannyl radical addition to imine system, the reaction of a-stannyl radical addition to hydrazone and oxime ether gave excellent cyclization yield. However, the phenomenon of 1,3-stannyl shift was not observed. There were difficulties in the synthesis and purification of imines 190 、 191, and we obtained massy products in the radical cyclization reactions. a-Stannylxanthate and a-stannylbromide functionalities were unstable under the reaction condition used for the synthesis of phenylimine.

並列關鍵字

Carbonyl ； a-Stannanyl Radicals ； Imine ； Cyclizations

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