Problem Set 8 – Reactions of enolate ions

1. Write equations for the steps in each of the following syntheses:

a. propanal ® 2-methyl-2-pentenal

b. propanal ® 2-methyl-2-penten-1-ol

c. acetophenone ® 1,3-diphenyl-2-propen-1-one

2. Pentaerythritol, a compound used to make explosives, can be prepared by reacting acetaldehyde with formaldehyde in a basic solution. The reaction successively yields three compounds of formulae C₃H₆O₂, C₄H₈O₃, and C₅H₁₀O₄. Compound C₅H₁₀O₄, in the presence of concentrated NaOH, is converted into two compounds, pentaerythritol, C₅H₁₂O₄, and a sodium salt, C₅H₉O₅Na. What is the structure of pentaerythritol?

3. 3-methyl-2-butenal reacts with dilute NaOH to yield dehydrocitral, C₁₀H₁₄O. Deduce the structure of dehydrocitral.

4. Intramolecular aldol cyclization of 2,5-heptanedione with dilute NaOH yields two enone products in the approximate ratio of 9:1. The major product has two singlet absorptions in its ¹H NMR spectrum at d = 1.65 ppm and d = 1.90 ppm. There are no absorptions in the range d = 3 – 10 ppm.

a. What is the structure of the major product?

b. What is the structure of the minor product?

5. 3-cyclohexenone reacts with dilute NaOH to form an equilibrium mixture with 2-cyclohexenone. Propose a mechanism for this reaction.

6. Treatment of compound “A” with Br₂/NaOH followed by acidification gives bromoform and pivalic acid, (CH₃)₃CCO₂H. What is the structure of “A”?

7. 1,3-diphenyl-2-propanone, in the presence of alcoholic KOH, reacts with diphenylethanedione to yield a dark purple, cyclic ketone (C₂₉H₂₀O). What is the structure of this ketone.

8. 2-methyl-3-buten-2-ol is one of the components of the sex pheromone of a destructive Scandinavian bark beetle. Propose a synthesis of this compound from acetone.