I was doing a reaction involving these two compounds in the presence of a base and I found that the trimethyl aconitate was deprotonated by the base against 2,4-pentanedione. I was expecting 2,4-pentanedione to be deprotonated instead of the trimethyl aconitate. This has made me to start looking for the pKa value of trimethyl aconitate.
I don't have the pKa value, but if you deprotonate the dione, you'll find that the anion has three resonance structures, two of which have the negative charge on oxygens. If you deprotonate trimethyl aconitate, the anion will have four resonance structures, two of which have the negative charge on carbons, and two of which have the negative charge on oxygen. Since the latter is has more charge delocalization, I would expect the trimethyl aconitate to be more acidic than the dione.
accord with Darren George + in the case of acetylacetone deprotonation occurs from OH in enol-form - higher kinetic acidity.
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