Ultrasound-promoted clean synthesis of 1-thiocarbamoyl-3-(2-hydroxyphenyl)-5-aryl-4,5-dihydro-1H-pyrazoles

Abstract

of important biological and pharmaceutical activities. In recent years, we described the synthesis of many heterocycles by non-traditional conditions, such as microwaves and ultrasound. In particular, the beneficial effects of ultrasonic irradiation are playing an increasing role in process chemistry, especially in cases where classical methods require drastic conditions or prolonged reaction times. These observations and our interest in clean production of heterocyclic compounds prompted us to apply ultrasound in the preparation of 1-thiocarbamoyl-3-(2-hydroxyphenyl)-5-aryl-4,5-dihydro-1H-pyrazoles. The best condition for preparing the target pyrazoles ( 5a-c ) was achieved when two equivalents of both KOH and thiosemicarbazide and 1 equivalent of the chalcones/flavanones ( 3,4a-c ) were sonicated for 30 minutes, affording the desired pure product in good yield (Scheme). In conclusion, we have developed a mild, convenient and environmentally friendly protocol for the preparation of target compounds under ultrasonic irradiation. Significant advantages of the method include the fact that: (i) the reaction is simple to execute; (ii) the products are isolated in good yields (61-76%); (iii) the work-up is very simple and (iv) the reaction time is short (30 min) .