To an equimolar mixture (1 mmol) of semicarbazide/thiosemicarbazide
and Z-styrylsulfonylacetic acid (3a-c), POCl3 (7 ml)
was added and heated under reflux for 4e6 h. The excess POCl3 was
removed under vacuum and the residue was poured onto crushed
ice. The resulting precipitate was filtered, washed with saturated
sodium bicarbonate solution and then with water. It was dried and
recrystallized from ethanol.