Budnikov Alexander S, Krylov Igor B, Lastovko Andrey V, Dolotov Roman A, Shevchenko Mikhail I, Terent'ev Alexander O
N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, 47 Leninsky prosp., 119991 Moscow, Russian Federation.
Org Biomol Chem. 2023 Oct 4;21(38):7758-7766. doi: 10.1039/d3ob00925d.
The intermolecular oxime radical addition to CC bonds was observed and studied for the first time. The diacetyliminoxyl radical was proposed as a model radical reagent for the study of oxime radical reactivity towards unsaturated substrates, which is important in the light of the active development of synthetic applications of oxime radicals. In the present work it was found that the diacetyliminoxyl radical reacts with vinylarenes and conjugated dienes to give radical addition products, whereas unconjugated alkenes can undergo radical addition or allylic hydrogen substitution by diacetyliminoxyl depending on the substrate structure. Remarkably, substituted alkenes give high yields of C-O coupling products despite the significant steric hindrance, whereas unsubstituted alkenes give lower yields of the C-O coupling products. The observed atypical C-O coupling yield dependence on the alkene structure was explained by the discovered ability of the diacetyliminoxyl radical to attack alkenes with the formation of a C-N bond instead of a C-O bond giving side products. This side process is not expected for sterically hindered alkenes due to lower steric availability of the N-atom in diacetyliminoxyl than that of the O-atom.
首次观察并研究了分子间肟自由基对碳 - 碳键的加成反应。二乙酰基亚胺氧基自由基被提议作为一种模型自由基试剂，用于研究肟自由基对不饱和底物的反应活性，鉴于肟自由基在合成应用方面的积极发展，这一点很重要。在本研究中发现，二乙酰基亚胺氧基自由基与乙烯基芳烃和共轭二烯反应生成自由基加成产物，而未共轭烯烃则可根据底物结构通过二乙酰基亚胺氧基进行自由基加成或烯丙基氢取代反应。值得注意的是，尽管存在显著的空间位阻，取代烯烃仍能高产率地生成碳 - 氧偶联产物，而未取代烯烃生成的碳 - 氧偶联产物产率较低。观察到的碳 - 氧偶联产率对烯烃结构的非典型依赖性，是由二乙酰基亚胺氧基自由基能够以形成碳 - 氮键而非碳 - 氧键的方式进攻烯烃从而产生副产物这一发现来解释的。由于二乙酰基亚胺氧基中氮原子的空间可及性低于氧原子，对于空间位阻较大的烯烃，这种副反应是不会发生的。
