takes place in the aqueous layer, and is shuttled to the organic layer with the reactants by tetrabutylammonium sulfate. The ketone catalyst is continuously regenerated in a catalytic cycle, and thus can catalyze the epoxidation in small amounts. The first step in the catalytic cycle reaction is the nucleophilic addition reaction of the oxone with the ketone group on the catalyst (intermediate 1). This forms the reactive intermediate number 2 species, the Criegee intermediate that can potentially lead to unwanted side reactions, such as the Baeyer-Villiger reaction (see below). The generation of intermediate species number 3 occurs under basic conditions, with a removal of the hydrogen from the hydroxy group to form a nucleophilic oxygen anion. The sulfate group facilitates the subsequent formation of the dioxirane, intermediate species number 4, by acting as a good leaving group during the 3-exo-tet cyclization. The activated dioxirane catalytic species then transfers an oxygen atom to the alkene, leading to a regeneration of the original catalyst. Side reactions A potential side reaction that may occur is the Baeyer-Villiger reaction of intermediate 2, where there is a rearrangement of the peroxy group that results in the formation of the relative ester. The extent of this side reaction declines with the rise of pH, and increases the nucleophilicity of the oxone, making basic conditions favorable for the overall epoxidation and reactivity of the catalytic species. Epoxidation mechanisms The oxygen from the dioxirane group generated on the organic catalyst is transferred to the alkene, in what is thought to be a concerted mechanism, although the presence of an oxygen anion intermediate through an Sn2 mechanism may transpire. Preparation of D-fructose derivative The catalyst is formed by reaction with acetone under basic conditions, with the hydroxyl groups of the fructose ring acting as nucleophiles, their nucleophilicity increased by the basic conditions created by potassium carbonate. The electron withdrawing substituents (alpha-ether groups) encourage the formation of the ketone from the oxidizing agent pyridinium chlorochromate by increasing the electrophilicity of the carbonyl carbon, via a stabilizing delocalization of the forming π C-C bonds into the σ* C-O bonds of the adjacent ethers. Transition states and enantiomeric selectivity There are two proposed transition states, whose geometries are speculated and not corroborated by experimental evidence, but are attributed to stereoelectronic effects. The spiro transition state is favored over the planar due to the non-bonding orbitals of the superior oxygen donating into the