An efficient one-pot preparation of alpha,beta-unsaturated-gamma-keto esters and amides has been developed. A zinc carbenoid-mediated chain extension of a beta-dicarbonyl substrate provides access to an intermediate zinc enolate, which is treated sequentially with a halogen and amine base. This method has been applied to a variety of ester and amide starting materials, as well as to amino acid-derived substrates and to a formal synthesis of (R,R)-(-)-pyrenophorin.