Melekhova Anna A, Smirnov Andrey S, Novikov Alexander S, Panikorovskii Taras L, Bokach Nadezhda A, Kukushkin Vadim Yu
Saint Petersburg State University, 7/9 Universitetskaya Nab., 199034 Saint Petersburg, Russian Federation.
ACS Omega. 2017 Apr 10;2(4):1380-1391. doi: 10.1021/acsomega.7b00130. eCollection 2017 Apr 30.
Cu-catalyzed cycloaddition (CA) of the ketonitrones, PhC=N(R')O (R' = Me, CHPh), to the disubstituted cyanamides, NCNR (R = Me, Et, (CH), (CH), (CH)O, CH, (CHPh), Ph(Me)), gives the corresponding 5-amino-substituted 2,3-dihydro-1,2,4-oxadiazoles (15 examples) in good to moderate yields. The reaction proceeds under mild conditions (CHCl, RT or 45 °C) and requires 10 mol % of Cu(NCMe) as the catalyst. The somewhat reduced yields are due to the individual properties of 2,3-dihydro-1,2,4-oxadiazoles, which easily undergo ring opening via N-O bond splitting. Results of density functional theory calculations reveal that the CA of ketonitrones to Cu-bound cyanamides is a concerted process, and the copper-catalyzed reaction is controlled by the predominant contribution of the HOMO-LUMO interaction (group I by Sustmann's classification). The metal-involving process is much more asynchronous and profitable from both kinetic and thermodynamic viewpoints than the hypothetical metal-free reaction.
酮亚硝基化合物PhC=N(R')O（R' = 甲基、苯甲基）与二取代氰胺NCNR（R = 甲基、乙基、(CH₂)₂、(CH₂)₃、(CH₂)₄O、CH₂(CH₂Ph)、苯甲基(甲基)）在铜催化下发生环加成反应，以良好至中等产率得到相应的5-氨基取代的2,3-二氢-1,2,4-恶二唑（15个实例）。该反应在温和条件下（氯仿，室温或45℃）进行，需要10 mol%的Cu(NCMe)₄₂作为催化剂。产率有所降低是由于2,3-二氢-1,2,4-恶二唑的独特性质，其容易通过N-O键断裂发生开环。密度泛函理论计算结果表明，酮亚硝基化合物与铜配位的氰胺的环加成反应是一个协同过程，铜催化反应受HOMO-LUMO相互作用的主要贡献控制（根据苏斯曼分类法为第一类）。从动力学和热力学观点来看，涉及金属的过程比假设的无金属反应更加不同步且更有利。
