The Claisen condensation enables the base-promoted formation of β-keto esters from esters bearing α-hydrogens, forging new C–C bonds through enolate attack on an ester carbonyl. Developed by Rainer Ludwig Claisen in the late 19th century, the reaction proceeds through ester enolate formation, carbon–carbon bond formation between two ester units, and subsequent acidic workup to yield the β-dicarbonyl product. Learn. Review. Repeat.