A new synthesis of 3H-pyrimidin-4-ones, characterized by four different sets of decorations, is presented. The strategy is based on the synthetic elaboration of readily available α-substituted β-ketoesters that, upon transformation into the corresponding acyl enamines, have been cyclized to give 6H-1,3-oxazin-6-ones. These reactive intermediates have been in turn cleanly converted into highly functionalized pyirimidinones, by treatment with an appropriate primary amine. The whole sequence does not need the use of any metal mediator or catalyst.