This reaction adds a 3-membered cycle ether (epoxide functional group) to an alkene using reagents called peroxy acids. These epoxides are highly strained, so they can react in very useful ring-opening reactions, which we will discuss later.
Peroxy acids are compounds with the general molecular formula RCO3H. The most common examples are MCPBA and MMPP. These are essentially the same molecule, just with different –R groups.
Concept: The mechanism of how peroxy acids make epoxides.4m
You typically won’t need to know this entire mechanism, but here is the first step:
Halohydrins can be deprotonated using a base to become a nucleophilic OH-. Once this anion is created, it can participate in intramolecular SN2 reaction with the halogen next to it, making a three-membered ring closure.