Galeotti Marco, Lee Woojin, Sisti Sergio, Casciotti Martina, Salamone Michela, Houk K N, Bietti Massimo
Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica 1, I-00133, Rome, Italy.
QBIS Research Group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain.
J Am Chem Soc. 2023 Nov 8;145(44):24021-24034. doi: 10.1021/jacs.3c07163. Epub 2023 Oct 24.
A product and DFT computational study on the reactions of 3-ethyl-3-(trifluoromethyl)dioxirane (ETFDO) with bicyclic and spirocyclic hydrocarbons bearing cyclopropyl groups was carried out. With bicyclo[.1.0]alkanes ( = 3-6), diastereoselective formation of the alcohol product derived from C-H bond hydroxylation was observed, accompanied by smaller amounts of products derived from oxygenation at other sites. With 1-methylbicyclo[4.1.0]heptane, rearranged products were also observed in addition to the unrearranged products deriving from oxygenation at the most activated C-H and C-H bonds. With spiro[2.5]octane and 6--butylspiro[2.5]octane, reaction with ETFDO occurred predominantly or exclusively at the axial C-H to give unrearranged oxygenation products, accompanied by smaller amounts of rearranged bicyclo[4.2.0]octan-1-ols. The good to outstanding site-selectivities and diastereoselectivities are paralleled by the calculated activation free energies for the corresponding reaction pathways. Computations show that the σ* orbitals of the bicyclo[.1.0]alkane or C-H bonds and spiro[2.5]octanes axial C-H bond hyperconjugatively interact with the Walsh orbitals of the cyclopropane ring, activating these bonds toward HAT to ETFDO. The detection of rearranged oxygenation products in the oxidation of 1-methylbicyclo[4.1.0]heptane, spiro[2.5]octane, and 6--butylspiro[2.5]octane provides unambiguous evidence for the involvement of cationic intermediates in these reactions, representing the first examples on the operation of ET pathways in dioxirane-mediated C()-H bond oxygenations. Computations support these findings, showing that formation of cationic intermediates is associated with specific stabilizing hyperconjugative interactions between the incipient carbon radical and the cyclopropane C-C bonding orbitals that trigger ET to the incipient dioxirane derived 1,1,1-trifluoro-2-hydroxy-2-butoxyl radical.
开展了一项关于3-乙基-3-(三氟甲基)二氧杂环丙烷(ETFDO)与含环丙基的双环和螺环烃反应的产物及密度泛函理论(DFT)计算研究。对于双环[.1.0]烷烃( = 3-6)，观察到通过C-H键羟基化衍生的醇产物的非对映选择性形成，同时伴有少量在其他位点氧化衍生的产物。对于1-甲基双环[4.1.0]庚烷，除了由最活泼的C-H和C-H键氧化产生的未重排产物外，还观察到了重排产物。对于螺[2.5]辛烷和6-丁基螺[2.5]辛烷，与ETFDO的反应主要或仅发生在轴向C-H处，生成未重排的氧化产物，同时伴有少量重排的双环[4.2.0]辛-1-醇。良好至优异的位点选择性和非对映选择性与相应反应途径计算出的活化自由能相当。计算表明，双环[.1.0]烷烃的σ*轨道或C-H键以及螺[2.5]辛烷的轴向C-H键与环丙烷环的沃尔什轨道发生超共轭相互作用，使这些键对ETFDO的氢原子转移(HAT)活化。在1-甲基双环[4.1.0]庚烷、螺[2.5]辛烷和6-丁基螺[2.5]辛烷氧化反应中检测到重排的氧化产物，为阳离子中间体参与这些反应提供了明确证据，这代表了二氧杂环丙烷介导的C()-H键氧化中电子转移(ET)途径运作的首个实例。计算支持了这些发现，表明阳离子中间体的形成与初始碳自由基和环丙烷C-C键轨道之间特定的稳定超共轭相互作用有关，该相互作用触发了向初始二氧杂环丙烷衍生的1,1,1-三氟-2-羟基-2-丁氧基自由基的电子转移。
