New class of bicyclic compounds derived from thiobarbituric acid with representative compound 1,3-diethyl-7-hydroxy-5,5,7-trimethyl-2-thioxo-1,2,3,5,6,7-hexahydro-4H-pyrano[2,3-d]pyrimidin-4-one. Preparation, crystal structure, mass spectrometry and IR spectroscopy