Dioxirane-mediated epoxidation of alkenes: The development of catalytic and asymmetric protocols

A practical, general and efficient protocol for the catalytic epoxidation of alkenes has been developed. The in situ generation of reactive dioxiranes capable of epoxidizing a variety of alkenes under biphasic conditions has been accomplished using phase transfer catalysts bearing a carbonyl group. Optimal epoxidation conditions employ 10 mol % of 1-dodecyl-1-methyl-4-oxopiperidinium trifluoromethanesulfonate (9d$\sp+$OTf$\sp-)$ in a $\rm CH\sb2Cl\sb2$/pH $7.5{-}8.0$ biphase using potassium monoperoxosulfate (Oxone) as the oxidant. Optimization of the conditions identified (1) slow addition rate, (2) pH 7.5-8.0, (3) n-dodecyl chain, and (4) the triflate salt as key experimental and structural variables.Efforts to develop an asymmetric epoxidation of alkene protocol using chiral, non-racemic ketone promoters are also reported. Chlorodifluoroketone promoter 36 was synthesized in 13 steps and subjected to our standard epoxidation of alkenes system and resulted in complete conversion when the reaction solution was emulsified and a level of asymmetric induction of 14% ee.Also described is a stereochemical study on the intramolecular hydrosilylation of $\alpha,\beta$-unsaturated esters. The intramolecular hydrosilylation of several 3-methyl-4-siloxy-2-butenoates afforded cis-disubstituted $\gamma$-lactones after desilylation. The diastereoinduction was sensitive to the bulk of the allylic substituents, but not to the groups on silicon. The origin of asymmetric induction is believed to be the A$\sp{1,2}$ strain from the $\beta$-methyl group.U of I OnlyETDs are only available to UIUC Users without author permissio