Preparation of unsubstituted dipyridine‐dibarbituric acid ylide through dimerization of pyridin‐2‐ylmethylenepyrimidinetrione as a reactive intermediate

Preparation of 5,5′‐(pyridin‐2‐ylmethylene)dipyrimidinetrione from barbituric acid and 2‐pyridinecarbox‐aldehyde in any polar solvent is a straightforward synthetic procedure, while preparation of the dipyridine‐dibarbituric acid ylide from the same starting materials is sensitive to the reaction media, pH, and temperature. For both products, the formation of the reactive intermediate 2‐pyridin‐2‐ylmethylenepyrimidinetrione is certain and this intermediate is a cross road for the reaction to be directed in one way or other. The experimental evidence for the formation of this important intermediate, as well as synthetic procedures for the preparation of both condensation products are presented.