The charge distribution in a peroxy acid puts a δ⁺ charge on the O atom of the OH group. (28) computationally studied the asymmetric induction, describing only the small core part of the catalyst by quantum mechanics. To describe crucial noncovalent interactions between the olefin and the substituted salen, they used empirical force fields. The cisON-oxo species resembles trans-L-oxo species in orientation of the reactive MnO3 fragment and is discussed first. Fig. Epoxidation in the presence of an axial ligand. Distortions of both types have been shown to increase the chirality content of the trans-MnV-oxo species (29). Synthetic and computational studies corroborate a diastereospecific aza-Prilezhaev-type mechanism. R. Mello, A. Alcalde-Aragonés, M. E. González Núñez, G. Asensio, J. Org. Even full DFT calculations will not be adequate, because the dispersion is not accounted for by DFT methods. The concerted mechanism is generally accepted and the stereochemistry of the alkene is preserved. The ground state of the MnV–trans-oxo species has been predicted to be singlet, triplet, or quintet. How is it often called the reaction of alkenes with peracids? Jie Lei, Gui-Ting Song, Liu-Jun He, Ya-Fei Luo, Dian-Yong Tang, Hui-Kuan Lin, Brendan Frett, Hong-yu Li, Zhong-Zhu Chen, Zhi-Gang Xu. Synthesis of Fluorine-Containing Molecular Entities Through Fluoride Ring Opening of Oxiranes and Aziridines. MnIV complexes. Numerous studies assume the MnV-oxo species postulated by Kochi and coworkers (20) to be the enantioselective oxidant. Online ISSN 1091-6490, Houk, K. N., DeMello, N. C., Condorski, K., Fennen, J. Synthesis of epoxides. Although our calculations show formation of the square pyramidal MnV–trans-oxo species to be impractical (42), this hypothetical “naked” oxo species helps to appreciate the axial-ligand effect and has been studied theoretically (5, 6, 22–25). The oxidant for the epoxidation is tert-Butyl hydroperoxide.The reaction is catalyzed by Ti(OiPr) 4, which binds the hydroperoxide, the allylic alcohol group, and the asymmetric tartrate ligand via oxygen atoms (putative transition state depicted below). One-pot construction of functionalized aziridines and maleimides Electron-rich alkenes are more reactive. The proposed reaction mechanism for epoxidation in the absence and presence of axial ligands is schematically drawn in Fig. Image credit: Stephanie Gamez (University of California San Diego, La Jolla, CA). 1. In particular, the quintet states of the cisON and cisNO oxo species are 4.6 and 7.3 kcal/mol higher than the corresponding triplet states. Information about how to use the RightsLink permission system can be found at During the epoxidation of alkenes, an oxygen atom is transferred from the peracid to the C=C double bond thus forming an oxirane ring. Notation used to describe olefin approaches to the reactive MnO3 fragment (A) and olefin orientations with D2, the dihedral angle MnO3C1C2 (B). The most dramatic enantioselectivity variations are observed for a synthetically important class of oxidants, organic peracids (30–34). This makes it an electrophilic atom that can add to alkenes. The syn addition is why the mechanism is the same for both symmetric and asymmetric alkenes. However, the relative energies of these transition states, {7.6; 6.9} and {7.2; 7.5} kcal/mol, are substantially lower than those of the quintet states. Are epoxides significantly more reactive than simple ethers? Why is epoxidation one of the most frequently used reactions in organic chemistry? There is also a secondary interaction between a lone pair orbital perpendicular to the plane of the peracid, nO(p) (HOMO) and the unoccupied π*C=C orbital (LUMO). Note that, because epoxidation by the MnIV–trans-L-oxo species is a bimolecular reaction with the activation energies >18 kcal/mol, it should not contribute to enantioselectivity. Because epoxidation by MnIV–trans-L-oxo species is unlikely, we do not discuss the ring closure in the corresponding MnIII–trans-L-radical intermediate. mono-perphthalate and peracetic acid are also employed. Our model comprised fully conjugated salen catalyst in (R,R) conformation without any bulky substituents and ethylene as olefin probe.