24. Enolate Chemistry: Reactions at the Alpha-Carbon

Provide the major product for the following reaction.

A ketone undergoes acid-catalyzed bromination, acid-catalyzed chlorination, racemization, and acid-catalyzed deuterium exchange at the ⍺-carbon. All of these reactions have similar rate constants.What does this tell you about the mechanisms of these reactions?

Predict the products of the following reactions.

(a) cyclopentanone + Br₂ in acetic acid

Acid-catalyzed halogenation is synthetically useful for converting ketones to α,β-unsaturated ketones, which are useful in Michael reactions (Section 22-18). Propose a method for converting cyclohexanone to cyclohex-2-en-1-one, an important synthetic starting material.

Propose a mechanism for the acid-catalyzed bromination of pentan-3-one.

Show how you would accomplish the following conversions in good yields. You may use any necessary reagents.

(a)

Propose mechanisms for the following reactions.

(e)

Show how the following compounds can be prepared from the given starting material:

a.