Conversion of barbituric acid to veronal
This paper from Tetrahedron Letters here details synthetic procedures using carbonyl compounds in solution with barbituric acid and Pt or Pd hydrogenation catalysyts to give reductive di-C alklyation. This includes examples of N-unsubstituted barbituric acids R1 = R2 = H. Using barbituric acid plus acetaldehyde should give you veronal in a single step.