Question

Example 2: Hydroboration reaction - conversion of alkynes to aldehydes

Answer 1

The reaction of the terminal alkyne with BH₃ followed by NaOH/H₂O₂ yields the aldehyde: cyclohexyl‑butanal (cyclohexyl–CH₂–CH₂–CHO).

Answer 2

• Step 1: Hydroboration of terminal alkyne
  $\text{R–C}\equiv\text{CH} + \ce{BH3} \longrightarrow \text{vinylborane intermediate}$
  The boron adds to the terminal carbon (anti‑Markovnikov) giving a vinylborane.

• Step 2: Oxidation with alkaline H₂O₂
  $\text{vinylborane} + \ce{H2O2}/\ce{NaOH} \longrightarrow \text{aldehyde}$
  The boron is replaced by OH, and tautomerisation leads to the aldehyde.

• Overall transformation

  Cyclohexyl‑butanal is formed with the carbonyl at the terminal carbon.