Claisen condensations retrosynthetic analysis

A retrosynthetic analysis of a,/J-unsaturated ketones leading to various methods of synthesis is outlined in Section 5.18.2, p. 798. These methods are equally applicable to aromatic aldehydes. Aromatic aldehydes condense with aliphatic or mixed alkyl aryl ketones in the presence of aqueous alkali to form a,[i-unsaturated ketones (the Claisen-Schmidt reaction). 

Let s try a synthesis. Suppose the target is ethyl 2-methyl-3-oxo-2-propylpentanoate. The presence of the /3-ketoester functionality suggests employing an alkylation reaction and/or an ester condensation. In one potential pathway, the propyl group can be attached by alkylation of a simpler /3-ketoester. Further retrosynthetic analysis suggests that the new target (ethyl 2-methyl-3-oxopentanoate) can be prepared from ethyl propanoate by a Claisen ester condensation. 

Retrosynthetic analysis clarifies the synthetic utility of the Claisen condensation... 

Retrosynthetic analysis of an aldol or Claisen product is easier if you first identify the new carbon-carbon bond. For dehydrated aldol (condensation) products this is the C=C double bond. 

---