A facile synthesis is reported for the construction of the five- and six-membered fused carbamate rings of an oxazolo[5,4]pyrimidin-2-one and a pyrimido[5,4][1,3]oxazin-2-one, respectively. The method utilises a controlled two-step procedure in which a reactive p-nitrophenylcarbamate intermediate ring closes upon treatment with base, affording the bicyclic pyrimidine-carbamate scaffolds in good yields.