Hydroboration and Oxymercuration of Alkynes
Hydroboration–oxidation of Alkyne
BH3 or R2BH (in THF) adds to alkynes in the same way it adds to alkenes. See the page here.
- In alkynes, enol is formed and immediately rearranged to aldehyde or ketone.
- Either BH3 or R2BH can be used with internal alkenes,
but the more sterically hindered R2BH (9-BBN) should be used with terminal alkynes - Hydroboration–oxidation of a terminal alkyne forms an aldehyde.
Oxymercuration-Demercuration
- Reaction of the alkyne with mercuric ion forms a cyclic mercurinium ion.
- A mercuric ketone is unstable and readily decompose in the presence of protons.
NaBH4 is not required. - Acid catalyzed addition of water (in the presence of mercuric ion) to a terminal alkyne forms a ketone.
