Dioxirane-olefin interaction

A kinetic study of the epoxidation showed the reaction to be of the first order with respect to both alkene and dioxirane174. A large steric effect was observed in the epoxidation of certain m/fnmv-dial kyIal kenes the cis compounds were found to exhibit reactivities one order of magnitude higher than the corresponding trans isomers. This large effect reflects a repulsive interaction between the substituents of the olefin and the dioxirane in the transition state (equation 25)9. 

The transition state model suggests that certain racemic olefins might be able to be kinetically resolved. Studies showed that a number of 1,6 and 1,3-disubstituted cyclohexenes could indeed efficiently be resolved with ketone 39 (Scheme 3.36) [61]. A rationalization for the kinetic resolution of 1,6-disubstituted cyclohexene using ketone 39 is shown in Scheme 3.37. Spiro C and D represent the major transition states for the epoxidation of each enantiomer of the racemic olefin. The destabilizing steric interaction between R2 and one of the dioxirane oxygens in spiro D disfavors this transition state, thus the epoxidation of the corresponding enantiomer proceeds at a lower rate. This kinetic resolution not only provides a valuable route to preparing certain chiral intermediates but also further validates the transition state model. 

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