This methodology involves synthesis of dibenzo xanthene tetraone by one pot multicomponent reaction of 2-hydroxy-1,4-naphthoquinone and pyrazole aldehyde in presence of p-toluenesulfonic acid (PTSA) as catalyst in ethylene glycol at 75-95 ºC. This protocol provides excellent yields (80-90%) involving simple workup procedures and purification techniques. By using several spectroscopic techniques the compounds were characterized.
A straightforward synthetic procedure for thioamides has been developed at 100 ºC using pyrazole aldehyde, a secondary amine, precipitated elemental sulphur and DMSO as solvent. The Willgerodt-Kindler reaction was successfully carried out by increasing the mole ratio of the precipitated sulphur and amine derivatives. The synthesized thioamides derivatives were characterized by 1H and 13C NMR, FT IR, HRMS spectrometric techniques. This method has various advantages, including high yields, a relatively rapid reaction time and the ability to operate in catalyst-free conditions.