Chapter 9: Alkynes

Summary

• Alkynes can also be hydrated to form enols that immediately tautomerise
• Terminal alkynes give aldehydes, internal alkynes give ketones
• Typical reagents (two steps) 1. BH₃ or B₂H₆ then 2) H₂O₂ / NaOH
• Electrophile : B atom
• Regioselectivity : Anti-Markovnikov, since the B is ultimately converted to the -OH.

• Hydroboration / oxidation of alkenes
• Hydration of alkynes

MECHANISM FOR HYDROBORATION OF ALKYNES

Mechanistically analgous to the hydroboration of alkenes to form the enol.
The resulting enol tautomerises to the aldehyde or ketone.

© Dr. Ian Hunt, Department of Chemistry