25. Condensation Chemistry

Describe how the following compounds can be prepared using an aldol addition in the first step of the synthesis:

c.

Propose a mechanism for the dehydration of diacetone alcohol to mesityl oxide

(a) in acid.

(b) in base.

Draw the products of the following reactions:

b.

Describe how the following compounds can be prepared using an aldol addition in the first step of the synthesis:

a.

The Knoevenagel condensation is a special case of the aldol condensation in which an active methylene compound reacts with an aldehyde or ketone, in the presence of a secondary amine as a basic catalyst, to produce a new C=C. Show the starting materials that made each of these by a Knoevenagel condensation.

(f)

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

(a)

What product can be isolated from the following aldol condensation reaction?

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

(b)

Propose a mechanism for the aldol condensation of cyclohexanone. Do you expect the equilibrium to favor the reactant or the product?

Propose mechanisms for the following reactions.

(a)

The Knoevenagel condensation is a special case of the aldol condensation in which an active methylene compound reacts with an aldehyde or ketone, in the presence of a secondary amine as a basic catalyst, to produce a new C=C. Show the starting materials that made each of these by a Knoevenagel condensation.

(e)

The following compounds can be synthesized by aldol condensations, followed by further reactions. (In each case, work backward from the target molecule to an aldol product, and show what compounds are needed for the condensation.)

(a)

Give the expected products for the aldol condensations of (c) pentan-3-one.