As in many synthetic procedures, an important challenge in ketone alkylation is choosing reagents and conditions that allow control of isomerism and of single vs. multiple substitution. β-Dicarbonyl compounds allow convenient alkylation and preparation of ketones and carboxylic acids. The aldol condensation, in which an α-position adds to a carbonyl group to generate a β-hydroxy- or an α,β-unsaturated carbonyl compound, can be driven to completion by removal of water. The Robinson annulation reaction is an important example of conjugate addition to α,β-unsaturated carbonyl compounds. α-Acylation of esters as in the Claisen condensation is a key step in the biosynthesis of fatty acids. Determining the constitutional structure of sugars posed a daunting challenge to early carbohydrate chemists.