What is the mechanism to convert an enol to a ketone under the basic conditions of the oxidation reaction that follows hydroboration?

Question

Emilia Alvarez · Accepted Answer

The hydroboration of a disubstituted alkyne begins with the following steps:

(RCH=CR-)₃B → 3RC≡CR + BH₃

CR-O)₃B + 3H₂O₂ → (RCH=CR-)₃B + 3H₂O

3RCH=CR-O⁻ + B(OH)₃ → (RCH=CR-O-)₃B + 3OH⁻

This is where the conversion process into a ketone begins.

Step 1: The enolate ion is a hybrid of resonance:

◷ RCH⁻-CR=O ◷ RCH=CR-O

Step 2: The hybrid's carbanion end assaults a water molecule:

O + H-OH → RCH₂-CR=O + ⁻OH

This substance is a ketone.

Lucy Alessi · Answer

undefined The mechanism involves the initial deprotonation of the enol by a base, forming an enolate intermediate. The enolate then undergoes tautomerization to the keto form, followed by oxidation of the keto group to form the ketone. This process is often achieved using reagents like hydrogen peroxide or potassium permanganate under basic conditions.