25. Condensation Chemistry

Consider the following reaction. Provide a stepwise mechanism to explain the given transformation.

Draw the product of the reaction of each of the following compounds with a base:

c.

Can 2,4-pentanedione undergo an intramolecular aldol addition? If so, why? If not, why not?

Draw the product of the reaction of each of the following compounds with a base:

d.

The following compound results from base-catalyzed aldol cyclization of a 2-substituted cyclohexanone.

(b) Propose a mechanism for the cyclization.

The following compound results from base-catalyzed aldol cyclization of a 2-substituted cyclohexanone.

(a) Show the diketone that would cyclize to give this product.

When cyclodecane-1,6-dione is treated with sodium carbonate, the product gives a UV spectrum similar to that of 1-acetyl-2-methylcyclopentene. Propose a structure for the product, and give a mechanism for its formation.

Show how octane-2,7-dione might cyclize to a cycloheptenone. Explain why ring closure to the cycloheptenone is not favored.

Draw the product of the reaction of each of the following compounds with a base:

a.

Draw the product of the reaction of each of the following compounds with a base:

b.

Propose mechanisms for the two Dieckmann condensations just shown.

Predict the products of the following aldol condensations. Show the products both before and after dehydration.

(b)

Predict the products of the following aldol condensations. Show the products both before and after dehydration.

(f)