| Autor: |
Galeotti M; 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., Lee W; Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States., Sisti S; Dipartimento di Scienze e Tecnologie Chimiche, Università 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133, Rome, Italy., Casciotti M; Dipartimento di Scienze e Tecnologie Chimiche, Università 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133, Rome, Italy., Salamone M; Dipartimento di Scienze e Tecnologie Chimiche, Università 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133, Rome, Italy., Houk KN; Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States., Bietti M; Dipartimento di Scienze e Tecnologie Chimiche, Università 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133, Rome, Italy. |
| Abstrakt: |
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[ n .1.0]alkanes ( n = 3-6), diastereoselective formation of the alcohol product derived from C 2 -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 2 -H and C 5 -H bonds. With spiro[2.5]octane and 6- tert -butylspiro[2.5]octane, reaction with ETFDO occurred predominantly or exclusively at the axial C 4 -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[ n .1.0]alkane cis or trans C 2 -H bonds and spiro[2.5]octanes axial C 4 -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- tert -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( sp 3 )-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. |
