1. Hydroboration-Oxidation of Alkynes
Recall hydroboration-oxidation of alkenes:

2. Hydroboration-Oxidation of Alkynes
The hydroboration of alkynes is analogous to that of alkenes
14.5 Conversion of Alkynes into Aldehydes and Ketones

3. Hydroboration-Oxidation of Alkynes
In principle, two additions of BH3 across the double bond could occur
This is limited to a single addition if a highly branched (sterically bulky) borane is used
14.5 Conversion of Alkynes into Aldehydes and Ketones

4. Hydroboration-Oxidation of Alkynes
Compare the following hydration reactions:
14.5 Conversion of Alkynes into Aldehydes and Ketones

5. Problems
What alkyne would you start with to prepare each of the following compounds by hydroboration-oxidation?

6. Catalytic Hydrogenation of Alkynes
Two additions normally occur
Hydrogenation may be stopped at the alkene if the reaction contains a catalyst poison
Salts of Pb2+ and certain nitrogen compounds are effective
14.6 Reduction of Alkynes

7. Catalytic Hydrogenation of Alkynes
The Pd/CaO3 catalyst poisoned with Pb(OAc)2 is known as Lindlar’s catalyst
14.6 Reduction of Alkynes

8. Reduction with Sodium in Liquid Ammonia
This method complements the poisoned catalyst method
14.6 Reduction of Alkynes

9. Mechanism of Reduction
14.6 Reduction of Alkynes

10. Mechanism of Reduction
14.6 Reduction of Alkynes

11. Problems
Give the products for the reactions of 5-decyne.