The synthesis of a series of diversely substituted pyrimidines under solvent-free conditions in good yields is described. Under microwave irradiation, a variety of nucleophilic substrates containing the N–C–N unit with β-dicarbonyl compounds, ethyl cyanoacetate, malononitrile, and chalcones was cyclized to give pyrimidines. A combinatorial type approach for a one-step synthesis has been developed where a ring-closing condensation is followed by spontaneous aromatization to afford 28 functionalized and aryl/alkyl substituted pyrimidines.