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(2H)‐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 nice yields, and pyridazin‐3(2H)‐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(2H)‐ones derivatives successfully reveals its practicability.