23 Important Concepts 23 Important Concepts 2 ehecoaoaot8weaaCao 5. 66 23 Important Concepts 1. Claisen Condensation – stoichiometric generation of a stable β-dicarbonyl anion in the presence of excess base 2. β-Dicarbonyl Compounds – hydrogens at the carbon between the carbonyl groups are acidic: • Electron-withdrawing power of two adjacent carbonyl groups • Resonance stabilization of the resulting anion 3. Mixed Claisen Condensations – between esters usually not selective, except with certain substrates (nonenolizable esters, intramolecular versions, ketones) 23 Important Concepts 4. 3-Ketoacids Are Unstable – they decarboxylate via a concerted mechanism through an aromatic transition state. • This, in conjunction with the nucleophilic reactivity of 3- ketoexter anions, allows the synthesis of substituted ketones and acids. 5. Alkanoyl (acyl) Anions – cannot be made by deprotonation of aldehydes. They have to be made as masked reactive intermediates or stoichiometric reagents by transformations of functional groups