Diastereoselective Cycloreductions and Cycloadditions Catalyzed by Co(dpm)<sub>2</sub>-Silane (dpm = 2,2,6,6-tetramethylheptane-3,5-dionate): Mechanism and Partitioning of Hydrometallative versus Anion Radical Pathways
作者:Long-Cheng Wang、Hye-Young Jang、Yeonsuk Roh、Vincent Lynch、Arthur J. Schultz、Xiaoping Wang、Michael J. Krische
DOI:10.1021/ja020223k
日期:2002.8.1
stereochemistry and electrochemical studies involving cathodic reduction of bis(enone) substrates. The collective experiments reveal competitive enone reduction pathways. Enone hydrometalation produces metallo-enolates en route to aldol and Michael cycloreduction products, that is, products derived from coupling at the alpha-position of the enone. Electron-transfer-mediated enone reduction produces metallo-oxy-pi-allyls
在苯基硅烷和 5 mol % 钴 (II) 双(2,2,6,6-四甲基庚烷-3,5-二酸)存在下,芳基取代的单烯酮单醛和双(烯酮)进行还原环化,得到合成羟醛和反迈克尔产品,分别。对于羟醛和迈克尔环还原,五元环和六元环的形成以高产率和高水平的非对映选择性发生。在 d(3)-苯基硅烷存在下,单烯酮单醛 1a 的环还原显示在烯酮 β 位掺入单个氘作为差向异构体的等摩尔混合物,推断在环化之前动力学形成的烯醇钴的快速异构化。氘代产物通过单晶中子衍射分析表征。对于双(烯酮)底物,硅烷源的调制能够分配竞争性迈克尔环还原和 [2 + 2] 环加成流形。对位取代苯乙酮衍生的双(烯酮)的研究表明,底物电子特征也直接分配环还原和环加成流形。通过检查烯酮几何对产物立体化学和电化学研究的影响,包括双(烯酮)底物的阴极还原,获得了进一步的机械洞察力。集体实验揭示了竞争性烯酮还原途径。烯酮加氢金属化在生成羟醛和迈克尔环