Spiro[5.5]undecane-2,4-dione-D6 is isotope labelled analog for Spiro[5.5]undecane-2,4-dione. Spiro[5.5]undecane-2,4-dione, is used as a reactant in the production of hydroxy-dimethyl-oxo-cyclohexenyl-dimethyl-tetrahydro-xanthenone which is an oral neuropeptide Y5 receptor antagonist.