Conjugate addition reactions of some methylidene 1-benzylpyrimidinetrione derivatives

1-Benzyl-2,4,6-pyrimidinetrione (1) reacts at C-5 with aldehydes and the isolated products can easily undergo base-induced transformations by Michael addition. On the contrary, the action Of POCl3 or piperidine/AcOH on the title trione afforded pyrimido{[}4,5 :4,5]furo{[}2,3-d]pyrimidine (16) and a dimer (17), respectively, which in turn, undergo cyclocondensation in AC(2)O.