Abstract3‐Oximino‐2,4‐pentanedione (1) and ethyl 2‐oximino‐3‐oxobutanoate (6) reacted with N,N‐dimethylformamide dimethylacetal (DFDA) to give 1,7‐bisdimethylamino‐3,5‐dioxo‐4‐methoximinohepta‐1,6‐diene (4) and ethyl 5‐dimethylamino‐2‐methoximino‐3‐oxo‐4‐pentenoate (8), respectively. When compounds 4 and 8 were treated with hydrazine hydrate, they gave O‐methyldipyrazol‐3(5)‐ylketoxime (5) and ethyl 2‐methoximino‐3(5)‐pyrazolylethanoate (9) together with its corresponding hydrazide 10, respectively. Upon action of DFDA on 3‐oximino‐2,4‐pentanedione (1) at ‐20° an explosive crystalline product was obtained. On the other hand, the reaction of 3‐acetoximino‐2,4‐pentanedione (11) with DFDA at ‐20° afforded a product which in ethanol solution, spontaneously deacetylated to give 1‐dimethylamino‐3,5‐dioxo‐4‐oximinohexa‐1‐ene (13). The structures of all the new compounds were assigned on the basis of satisfactory analytical and spectroscopic data.