Chapter 18, Problem 18.89P

Interpretation Introduction

Interpretation:

Mechanism for the reaction in which an $\text{α,β-}$ unsaturated carbonyl compound is treated with ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ under basic conditions is to be drawn.

Concept introduction:

${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ is a weak acid that can be deprotonated by a strong base like NaOH, producing $\text{HO}-{\text{O}}^{-}$. This is not a very strong nucleophile, so it adds to an $\text{α,β-}$ unsaturated carbonyl compound in a conjugate manner. The addition produces an enolate. Resonance stabilization of the enolate produces a carbanion, with the negative charge shifting from the oxygen to the $\text{α-}$ carbon. This carbanion then acts as a nucleophile in the next step, displacing the hydroxide. Hydroxide is normally a poor leaving group, but in this case, the weak peroxide $\text{O}-\text{O}$ bond makes it possible. This results in the formation of the epoxide ring. The hydroxide ion is regenerated in the last step, making it a base catalyzed reaction.