Transition‐metal‐free Cyclization of Mucohalic Acids with Sulfonyl Hydrazides: An Approach to Pyridazin‐3(2H)‐ones

Abstract An eco‐friendly and efficient synthesis of pyridazin‐3(2 H )‐ones from aromatic sulfonyl hydrazides and mucohalic acids has been developed. This facile strategy is carried out smoothly via the promotion of simple organic acid p ‐toluenesulfonic acid, and able to form two C−N bonds and a heterocycle linking a potentially bioactive sulfonyl group at one‐step. The protocol is tolerant to various readily available substrates in good yields, and pyridazin‐3(2 H )‐ones as the desired products are key structural fragments of many bioactive compounds. More importantly, the gram‐scale cyclization reaction of aromatic sulfonyl hydrazides and mucohalic acids as a novel approach to pyridazin‐3(2 H )‐ones derivatives successfully reveals its practicability.