Q9-6P - Organic Chemistry (Mcmurry)

Question

What alkyne would you start with to prepare each of the following compounds by a hydroboration–oxidation reaction?

Step-by-Step Solution

Answer

Answer:

Step 1: Hydroboration – oxidation reaction

Borane adds rapidly to an alkyne resulting in vinylic borane can be oxidized by to 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

Step 2: Formation of compound a

Terminal alkyne undergoes two additions, giving a doubly hydroborated intermediate. Oxidation with H₂O₂ replaces both boron atoms with oxygen and generates the aldehyde.

Step 3: Formation of compound b

Internal alkyne undergoes two additions, giving a doubly hydroborated intermediate. Oxidation with H₂O₂ replaces both boron atoms with oxygen and generates ketone.