3204-04-4Relevant articles and documents
Epoxidation by Dimethyldioxirane: Electronic and Steric Effects
Baumstark, A. L.,Vasquez, P. C.
, p. 3437 - 3439 (1988)
The reaction of dimethyldioxirane (1) with a series of di- and monosubstituted alkenes 2-17 produced the corresponding epoxides in high yield.A kinetic study of the epoxidation of 2-17 by 1 in dried acetone showed the reaction to be of the first order with respect to both alkene and dioxirane.For certain cis/trans-dialkylalkenes, the cis compounds were found to be of ca. 10-fold greater reactivity than the corresponding trans isomers.However, cis/trans pairs of alkenes with phenyl substituents were found to be of similar reactivity.A kinetic study on the reaction of a series of substituted styrenes yielded an excellent LFER with a ρ value of -0.90.Addition of water to dioxirane reactions in acetone increased the observed rates of epoxidation.However, a tertiary allylic alcohol was found to undergo epoxidation slower than expected.The mechanistic implications of the results are discussed.
Activation parameters for the epoxidation of substituted cis/trans pairs of 1,2-dialkylalkenes by dimethyldioxirane
Crow, Brian S.,Winkeljohn, W. Rucks,Navarro-Eisenstein, Angela,Michelena-Baez, Elba,Franklin, Paul J.,Vasquez, Pedro C.,Baumstark, Al
, p. 4642 - 4647 (2007/10/03)
The first activation parameter data for the reaction of dimethyldioxirane (1) with five cis/trans pairs of alkenes are reported. The epoxidation of cis-1,2-dialkylalkenes (2cis: R1 = Me, R2 = iPr; 3cis: R1 = Me, R2 = tBu; 4cis: R1 = R2 = Et; 5cis: R1 = Et, R2 = iPr; 6cis: R1 = Et, R2 = tBu) and trans-1,2-dialkylalkenes (2trans: R1 = Me, R2 = iPr; 3 trans: R1 = Me, R2 = tBu; 4trans: R1 = R2 = Et; 5trans: R1 = Et, R2 = iPr; 6trans: R1 = Et, R2 = tBu) by 1 produced the corresponding epoxides, quantitatively and stereospecifically, as the sole observable products. Activation parameters of the epoxidation of the five pairs of alkenes, 2cis-6cis and 2trans-6trans, by 1 were determined using the Arrhenius method. Enhanced selectivity for cis- vs. trans-alkene epoxidation was observed at lower temperatures. In general, the ΔG? terms were larger and showed more variability for the reaction of 1 with trans-alkenes as compared to those for the corresponding cis isomers. The ΔH? terms mirrored trends observed in ΔG ? because ΔS? terms for all ten of the compounds were roughly identical. The ΔΔG? values, a comparison of the trans to the cis isomer data, yielded positive values of 1.2 to 1.8 kcal/mol for the five sets of data and appeared to be dependent on relative steric interactions. The experimental activation parameter data, consistent with predictions from ab initio calculations based on a spiro transition-state model, showed that the lower reactivity of trans-alkenes is due to enthalpy factors. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
