Claisen condensation is a chemical reaction that occurs between two esters or an ester and a carbonyl compound in the presence of a strong base. This reaction results in the formation of a β-keto ester or a β-diketone. The process involves the deprotonation of an ester to form an enolate ion, which then attacks the carbonyl carbon of another ester or carbonyl compound. The reaction is named after the German chemist Heinrich Claisen, who first described it in the 19th century. Claisen condensation is significant in organic synthesis, as it allows for the construction of complex molecules and is widely used in the preparation of various pharmaceuticals and natural products.