meta-Chloroperoxybenzoic acid (mCPBA) and other peroxyacids (RCO3H) react with alkenes to form epoxides:

If this reaction adds stereochemistry to the molecule, the two epoxide bonds are added in syn addition and are always in the same plane. This reaction also maintains the cis/trans positioning of functional groups after the epoxide ring has been formed:

Same plane

No stereocenters

The reaction mechanism is depicted below:

In the first step, many electron movements are shown but this depicts more of an intermediate product than a discrete step. The electrons from the alkene bond react with the OH group of mCPBA to form a ring structure. Simultaneously, electrons from the Oxygen-Oxygen bond shift over to mCPBA from the OH group, allowing the double bonded O on mCPBA to attack the H atom from the OH group, resulting in epoxide formation

The reagents used for this reaction are mCPBA or other peroxyacids (RCO3H).