Ethers are generally unreactive. However, epoxides (3-membered cyclic ethers) are highly strained, so they are able to react with nucleophiles in ways a typical ether could not. Let’s take a look.
Concept #1: Acid-Catalyzed Epoxide Ring-Opening
Acid-catalyzed ring openings favor addition to the MOST substituted carbon (thermodynamic control)
Concept #2: Base-Catalyzed Epoxide Ring-Opening
Base-catalyzed ring openings favor addition to the LEAST substituted carbon (kinetic control).