Condensation of several arylhydrazones with chlorocarbonyl phenyl ketene gave 2-(arylmethylidene)-5-oxo-1,4-diphenyl-2,5-dihydro-1H-pyrazol-2-ium-3-olates in high yields.
POTTS K. T.; KANEMASA S.; ZVILICHOVSKY G., J. AMER. CHEM. SOC., 1980, 102, NO 11, 3971-3972