DMAP‐Promoted Dehalogenative Sulfonylation of 4,5‐Dihalo‐Pyridazin‐3(2 H )‐Ones With Arylsulfonyl Hydrazides: An Approach to 4‐Arylsulfonylpyridazin‐3(2 H )‐Ones

A dehalogenative sulfonylation of 4,5‐dihalo‐pyridazin‐3(2 H )‐ones with arylsulfonyl hydrazides under mild conditions for the synthesis of 4‐arylsulfonyl pyridazin‐3(2 H )‐ones is developed for the first time. The transformation also avoids the use of transition‐metal catalysts, oxidants, and reductants. Notably, due to the relatively low activity of the C‐4 site of pyridazin‐3(2 H )‐ones, there are few reports on functionalization reactions at this position before, especially on sulfonylation. Thus, this strategy is of great significance to expand both the synthetic range of potential functional pyridazin‐3(2 H )‐one compounds and the application scope of arylsulfonyl hydrazines as a kind of multifunctional reagents.