Catalytic Oxidative Cyclization of 2'-Arylbenzaldehyde Oxime Ethers under Photoinduced Electron Transfer Conditions.
Catalytic Oxidative Cyclization of 2'-Arylbenzaldehyde Oxime Ethers under Photoinduced Electron Transfer Conditions.
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DOI：
10.1021/jo502324z
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发表时间：
2015-01-02
期刊：
影响因子：
--
通讯作者：
de Lijser HJ
中科院分区：
文献类型：
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作者：
Hofstra JL;Grassbaugh BR;Tran QM;Armada NR;de Lijser HJ
合成了一系列 2'-芳基苯甲醛肟醚，并显示在乙腈中的 9,10-二氰基蒽存在下，经照射可生成相应的菲啶。机理研究表明，氧化环化反应序列是由电子转移步骤引发的，随后芳基环对肟醚的氮进行亲核攻击。下凹的哈米特图可能是具有强给电子取代基的自由基阳离子物质中电荷分布变化的结果，产生了亲电子性较低的氮原子和环化产物量的减少。该反应具有选择性（与涉及醛肟醚的其他光化学反应不同，不会形成腈副产物），并且在使用具有间位取代基的 2'-芳基时具有区域特异性，使该反应成为制备取代菲啶的有用替代方法。
A series of 2′-arylbenzaldehyde oxime ethers were synthesized and shown to generate the corresponding phenanthridines upon irradiation in the presence of 9,10-dicyanoanthracene in acetonitrile. Mechanistic studies suggest that the oxidative cyclization reaction sequence is initiated by an electron transfer step followed by nucleophilic attack of the aryl ring onto the nitrogen of the oxime ether. A concave downward Hammett plot is presumably the result of a change in charge distribution in the radical cation species with strongly electron-donating substituents that yields a less electrophilic nitrogen atom and a decreased amount of cyclized product. The reaction is selective (no nitrile byproduct is formed unlike other photochemical reactions involving aldoxime ethers) as well as regiospecific when using 2′-aryl groups with meta-substituents, making this reaction a useful alternative for preparing substituted phenanthridines.