Question

How would you prepare the following carbonyl compounds starting from an alkyne (reddish-brown Br)?

b.

Short answer

Answer

Step-by-step solution

Hydroboration – oxidation reaction

Borane adds rapidly to an alkyne resulting in vinylic borane can be oxidized by H₂O₂to yield an enol. Tautomerization then gives either a ketone or an aldehyde.

• The terminal alkyne leads to the formation of aldehyde
• The internal alkyne leads to the formation of ketone

 Formation of compound a

Terminal alkyne undergoes two additions, giving a doubly hydroborated intermediate. Oxidation with H₂O₂replaces both boron atoms with oxygen and generates the aldehyde.