Diastereoselective Radical-Type Cyclopropanation of Electron-Deficient Alkenes Mediated by the Highly Active Cobalt(II) Tetramethyltetraaza[14]annulene Catalyst.
Diastereoselective Radical-Type Cyclopropanation of Electron-Deficient Alkenes Mediated by the Highly Active Cobalt(II) Tetramethyltetraaza[14]annulene Catalyst.
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DOI：
10.1002/cctc.201601568
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发表时间：
2017-04-21
期刊：
影响因子：
4.5
通讯作者：
de Bruin B
中科院分区：
文献类型：
--
作者：
Chirila A;Gopal Das B;Paul ND;de Bruin B
提出了一种利用缺电子烯烃催化合成环丙烷的新方案，该方案由一系列价格合理、易于合成且具有高活性的取代钴（II）四氮杂[14]环烯催化。这些催化剂与使用甲酰腙钠盐作为重氮化合物的前体在一锅催化转化中相容，以几乎定量的收率提供所需的环丙烷。该反应利用钴配合物的金属特性来激活重氮化合物。该反应实际而快速，并且从现成的起始材料中进行。它不需要缓慢添加重氮试剂或甲苯腙盐或加热，并且耐受许多溶剂，其中包括质子溶剂，如MeOH。由四甲基四氮环烯配体衍生的CoII配合物比钴（II）卟啉更容易制备，具有相似的催化碳自由基反应活性，但更活跃。反应在20°C下几分钟内进行，甚至在- 78°C下几小时内进行。该催化体系稳定性好，可以用烯烃或重氮试剂作为限制剂，完全抑制了重氮化合物的二聚化。该方法已应用于多种取代环丙烷的合成。对不同的底物具有高的收率和选择性，对反式环丙烷具有固有的偏好。
A new protocol for the catalytic synthesis of cyclopropanes using electron‐deficient alkenes is presented, which is catalysed by a series of affordable, easy to synthesise and highly active substituted cobalt(II) tetraaza[14]annulenes. These catalysts are compatible with the use of sodium tosylhydrazone salts as precursors to diazo compounds in one‐pot catalytic transformations to afford the desired cyclopropanes in almost quantitative yields. The reaction takes advantage of the metalloradical character of the Co complexes to activate the diazo compounds. The reaction is practical and fast, and proceeds from readily available starting materials. It does not require the slow addition of diazo reagents or tosylhydrazone salts or heating and tolerates many solvents, which include protic ones such as MeOH. The CoII complexes derived from the tetramethyltetraaza[14]annulene ligand are easier to prepare than cobalt(II) porphyrins and present a similar catalytic carbene radical reactivity but are more active. The reaction proceeds at 20 °C in a matter of minutes and even at −78 °C in a few hours. The catalytic system is robust and can operate with either the alkene or the diazo reagent as the limiting reagent, which inhibits the dimerisation of diazo compounds totally. The protocol has been applied to synthesise a variety of substituted cyclopropanes. High yields and selectivities were achieved for various substrates with an intrinsic preference for trans cyclopropanes.