Peroxyacids stereochemistry

Peroxyacids transfer an oxygen atom to the alkene with syn stereochemistry—both C-0 bonds form on the same face of the double bond-through a one-step mechanism without intermediates. The oxygen atom farthest from the carbonyl group is the one transferred. 

The following examples use m-chloroperoxybenzoic acid (MCPBA), a common epoxidizing reagent, to convert alkenes to epoxides having the same cis or trans stereochemistry. MCPBA is used for its desirable solubility properties The peroxyacid dissolves, then the spent acid precipitates out of solution. 

The three most common alkene oxidation reactions are epoxidation, dihydrox-ylation, and ozonolysis. Epoxides are formed when an alkene is treated with a peroxyacid, such as mCPBA. Since both C-O bonds are formed in the same step (described as a concerted mechanism), the stereochemistry of the starting alkene is preserved in the product. 

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