25. Condensation Chemistry

What aldol addition product is formed from each of the following compounds?

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.

(d)

Many of the condensations we have studied are reversible. The reverse reactions are often given the prefix retro-, the Latin word meaning “backward.” Propose mechanisms to account for the following reactions.

(a)

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

b.

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.

(b)

A student tried to prepare the following compounds using aldol condensations. Which of these compounds was she successful in synthesizing? Explain why the other syntheses were not successful.

Provide the mechanism for the following transformation.

Propose mechanisms for the reactions shown in Problems 22-62 part (a).

Predict the products of these reaction sequences.

Give the expected products for the aldol condensations of (b) phenylacetaldehyde.

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

(c)