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

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

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

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

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

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

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

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

Mechanism of Reduction 14.6 Reduction of Alkynes

Mechanism of Reduction 14.6 Reduction of Alkynes

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