Synthesis of some Thiadiazoline Derivatives from 2- Phenyl Chroman-4-one

Phenyl chroman-4-one 1(a-g) were synthesized by Pechmann condensation of proper phenol with cinnamic acid using poly phosphoric acid. Reactions of their derivatives with thiosemicarbazide were carried out using two methods, method A, using refluxing ethanol, gave low yield (17-20%). This method was modified to increase the yield using solvent free microwave irradiation technique, (method B), which improved the yield up to (30-40%). The treatment of these thiosemicabazones 2(a-g) with excess acetic anhydrid gave substituted thiadiazoline derivatives 3(a-g). The structure of these compounds was confirmed by IR, UV and NMR spectra in addition to their physical properties. On the other hand, the calculated values of the heat of formation and steric energy were established for compounds 2(a-g) and 3(a-g).