Abstract Some intermediates and by-products of the title reaction, known to yield 6- hydrazinopyridazine-3-one derivatives, were isolated or detected when the amount of hydrazine hydrate used to react with two model β-cyano esters was reduced to less than two equivalents. N'-(1-amino-4-hydrazino-4-oxo-2-phenylbutyli-dene)-4-hydrazino-4-oxo-2- phenylbutanehydrazonamide and 3, 3, 8, 8-tetramethyl-2, 3, 7, 8-tetrahydro-1H, 6H- ...