Reaction of epoxides with nucleophiles under basic conditions
Description: When epoxides are treated with negatively charged nucleophiles, they will add to the least substituted position of the epoxide in an SN2 reaction.
Notes: Recall that epoxides are unlike normal ethers in that they have considerable ring strain due to the 3 membered ring.
- The purpose of the acid in the second step is to protonate the negatively charged oxygen that is formed when the epoxide is opened. This results in formation of a neutral alcohol.
- Where addition occurs to a stereocenter, the stereochemistry of the carbon will invert.
- Some examples of nucleophiles that will add to epoxides include hydroxyl (HO-) alkoxy (RO-), Grignard reagents and (sometimes) organocuprates (Gilman reagents)
Notes: This depicts opening of an epoxide by a Grignard reagent. The second step is protonation of the oxygen with H3O(+).
Note that there is nothing special about Cl(-) here, it’s just a spectator ion with H3O(+)