6-(Tertiary amino)uracils 1 react with dimethyl acetylenedicarboxylate (DMAD) to afford 5,6-dihydropyrrolo[2,3-d]pyrimidines 3a and 3b and the tricyclic analogues 3c–fvia 1,5-electrocyclisation in excellent yields, whereas suitably functionalized uracil derivatives 5 undergo intramolecular 1,6-cycloaddition reactions to afford 5,6,7,8-tetrahydropyrido[2,3-d]pyrimidines 6a and 6b and the tricyclic analogues 6c–h in high yields.