Chiral dioxirane protocol

Shi and co-workers <97JOC2328, 97JA11224> have optimized their chiral dioxirane protocol for the asymmetric epoxidation of non-functionalized rra/i.v-olefins (e.g., 44), such that the chiral ketone 42 can be used in catalytic quantities with potassium peroxomonosulfate (Oxone) as the stoichiometric oxidant. The key to preserving the lifetime of the chiral auxiliary is pH control during the reaction the optimum range was found to be 10.5 or above, which is conveniently maintained with potassium carbonate. 

The spirodiepoxide 1 is an intriguing new approach to relative and absolute stereocontrol. It will be interesting to see what other nucleophiles can be used in the opening. It is possible that a chiral oxygen transfer reagent, such as the dioxirane prepared by the Shi protocol, would convert 12 to 1 with improved diastereoselectivity (double diastereoselection). 

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