Krapcho decarboxylation
The Krapcho decarboxylation is the chemical reaction of esters with halide anions. The ester must contain an electron-withdrawing group in the beta position, such as β-ketoesters, malonic esters, α-cyanoesters, or α-sulfonylesters. It works best with methyl esters, since it is an SN2-reaction at carbon. It is driven by the entropy of the overall reaction, as the byproducts chloromethane and CO2 are lost as gases. The reaction is a useful synthetic procedure to hydrolyze and decarboxylate malonic esters because it only cleaves one of the ester groups. The alternative way destroys both of the ester groups and a subsequent reaction is usually used to regenerate the alkylated ester.
