Abstract Reaction of open-chain and cyclic sym-1, 3-diones with N, N-dimethylformamide dimethyl acetal gave, generally in high yield, a series of sym-2-dimethylaminomethylene-1, 3-diones which reacted with phenylhydrazine and methylhydrazine to afford, generally in satisfactory yield, a number of 1, 5-disubstituted 4-acylpyrazoles. The applications and limits of this new pyrazole synthesis are presented and discussed.