The methyl acetoacetate dianion
The dianions of β-keto esters are easily generated by adding first sodium hydride, which removes the most acidic proton (that of the central CH2), and then butyllithium, which removes one from the terminal methyl. Huckin and Weiler (1974) showed that the dianion is alkylated selectively at the γ carbon.
With prenyl bromide a β-keto ester containing an isoprene unit is obtained, a useful intermediate in terpene synthesis; the β-keto ester group then allows further alkylations, condensations or decarboxylation.