Synthesis of new 6-X-piperonal mesoionic derivatives by microwave irradiation

The 1,3,4-thiadiazolium-2-phenylamine chlorides are precursors of mesoionic compounds, a special class of heterocyclic compounds with diverse biological activities.1,2 The interesting structure of the 1,3,4-thiadiazolium-2-phenylamine class of compounds and the promising therapeutic applications therefrom led us to synthesize a new series of such compounds. In the present work, the synthesis and characterization of novel piperonal 1,3,4-thiadiazolium-2-phenylamine mesoionic derivatives were described. The mesoionic compounds 5-(3’,4’-methylenedioxy-6’-X)-1,3,4-thiadiazolium-2-(4’’--phenyl)-amine chlorides derived from 6-X-piperonal, where synthesized by microwave assisted irradiation. The convergent strategy involved the reaction of the appropriate 6-X-piperonal and N1-Y-phenyl-N4-thiosemicarbazides in the presence of SOCl2 as a Lewis acid catalyst.3 Both, the 6-X-piperonal aldehyde and thiosemicarbazides were also prepared in this work.4 The reaction mixture was irradiated in a microwave oven for 5 min at 100 kW. The products were obtained as fine crystals in high-purity and satisfactory yields, 60-95%, after a short irradiation time, and were fully characterized by IR, 1H and 13C NMR