Abstract A new practical and efficient synthesis of 1, 3, 5-trisubstituted pyrazoles has been developed by reacting of hydrazonoyl halides with β-oxophosphonates under mild conditions in good yields with excellent regioselectivity. This process employs an addition– elimination sequence. Wide scope, functional group compatibility has been established.
![ethyl 2-chloro-2-[(4-chlorophenyl)hydrazinylidene]acetate Structure](https://image.chemsrc.com/caspic/175/27143-09-5.png)
