Synthesis and dynamic 1H NMR spectroscopic study of 1,4,6,7,8,9-hexahydro-3-methyl-1,4-diphenyl-7-thioxo-5H-pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidin-5-one

Abstract

3-Methyl-1-aryl-2-pyrazoline-5-one, aromatic aldehyde, and 6-amino-2-thiouracil were used for the synthesis of a variety of 1,4,6,7,8,9-hexahydro-3-methyl-1,4-diaryl-7-thioxo-5H-pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidin-5-ones via a one-pot three-component reaction. The reaction was performed in the presence of piperidine as a catalyst that leads to reducing reaction time and improves synthetic efficiency. The free-energy barrier (ΔG ≠) for prototropic tautomerism in title compound is determined by dynamic 1H NMR studies to be 67 kJ mol−1.