The reaction between barbituric acid or 2-thiobarbituric acid and different benzaldehydes, dependent upon the applied reaction conditions, selectively yields three different product types, i.e. 5-benzylidene(thio)barbituric acids II, symetric Michael adducts III or 5-phenyl-1H-pyrano[2,3-d]pyrimidine-2,4(3H,5H)-diones and 5-phenyl-2-thioxo-2,3-dihydro-1H-pyrano[2,3-d]pyrimidin-4(5H)-ones IV. Th...

The five-membered furanose ring is a central component of the chemical structure of biological nucleic acids. The conformations of the furanose ring can be analytically described using the concept of pseudorotation, and for RNA and DNA they are dominated by the C2'-endo and C3'-endo conformers. While the free energy difference between these two conformers can be inferred from NMR measurements, ...