3-Oxo-1,4-piperidinedicarboxylic Acid 1-(1,1-Dimethylethyl) 4-Methyl Ester is used as a reagent in the synthesis of fused pyrimidines as histamine H4 receptor antagonists. 3-Oxo-1,4-piperidinedicarboxylic Acid 1-(1,1-Dimethylethyl) 4-Methyl Ester is also used as a reagent in the synthesis of heterocycles containing a 4-substituted pyrimidine subunit for pharmaceutical use as mGluR1 antagonists for treatment of migraine.