Oxymercuration of Alkenes in the Presence of Alcohols: Oxymercuration of alkenes is a stepwise reaction involving a bridged mercurinium ion intermediate. In asymmetrical alkenes, the alkene carbon which would form the most stable carbocation will bear more of the positive charge and, in alcohols, will be attacked by alkoxide anion (or the alcohol) to give the addition intermediate; rearrangements do not occur, but the orientation follows Markovnikov's Rule. In a second step, BH₄^- is used to remove the mercury and give the final product.

Formation of Epoxides by Oxidation of Alkenes: Alkenes undergo partial oxidation with peracids to form epoxides. A stable and useful reagent for this reaction is the magnesium salt of monoperoxyphthalate (MMPP).

Formation of Epoxides by an Internal S_N2 Reaction in Halohydrins: Halohydrins (prepared by the addition of HOX to an alkene) undergo an internal S_N2 reaction in the presence of strong base (NaOH) to give epoxides.

Reactions

Cleavage of Ethers with HI: Ethers undergo cleavage in the presence of aqueous HI to give the corresponding alkyl iodide. Attack will be at the least hindered carbon and E1 reactions, with carbocation intermediates, are common with ethers with groups which can form stable carbocations.

Ring-Opening Reactions of Epoxides: The three-membered ring of epoxides is highly strained and undergoes ring-opening reactions with a variety of nucleophiles, as shown below.

For reactions involving acid catalysis, the first step involves protonation of the ether oxygen to make it a better leaving group, followed by nucleophilic attack.

More examples: