Formation of carbon–carbon bonds: base-catalyzed reactions
The formation of carbon–carbon bonds by base-catalyzed reactions is closely related to their formation from organometallic reagents. In each method negatively polarized carbon reacts with the electrophilic carbon of carbonyl groups, alkyl halides, and related compounds. In practice, reaction at carbon normally dominates in each case, probably because the products are thermodynamically more stable than those derived by reaction through oxygen, this difference in stability being reflected in the transition states for the processes. The Stobbe condensation leads to the attachment of a three-carbon chain to a ketonic carbon atom, whereas the condensations so far described lead to the attachment of a two-carbon chain. The aldol reaction is one of the most commonly used methods for forming new C—C bonds. Cinnamic acid may be prepared from benzaldehyde in each of the following ways: Claisen reaction, Perkin reaction, Knoevenagel reaction, and Reformatsky reaction.