25. Condensation Chemistry

Propose mechanisms for the two Dieckmann condensations just shown.

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

(b) Propose a mechanism for the cyclization.

Which product is the most likely intramolecular aldol addition product formed when $O_2$-hexanedione is treated with base and then acid workup?

What is the major product formed when ${\mathrm{CH}}_2\mathrm{COCH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}$ (hexane-2,6-dione) undergoes intramolecular aldol condensation under basic conditions?

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)

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

d.

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

b.

Some (but not all) of the following keto esters can be formed by Dieckmann condensations. Determine which ones are possible, and draw the starting diesters.

(a)

(b)

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

(f)

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.

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.

Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.

(e)