Abstract
A formal [4 + 2] reaction for the synthesis of 5’-sulfonyl-4’-aryl-3-cyano substituted pyridazine compounds from the reaction between vinylogus enaminonitrile and sulfonyl hydrazides is reported. The key features of our pyridazine synthesis include the transamidation of vinylogus enaminonitrile with sulfonyl hydrazide, radical sulfonylation of the resulting intermediate, and subsequent 6-endo-trig radical cyclization. This reaction proceeds smoothly to deliver a series of pyridazine derivatives in good to high yields. We also found that the sulfonyl group of the synthesized pyridazines can be transformed into C-, O-, or N-containing functional groups. A gram scale experiment and a diverse transformation of synthesized pyridazines were also performed to validate the practicability of our developed process. In the synthesis of sulfonyl substituted pyridazines, a 6-endo-trig cyclization via a radical pathway is both kinetically and thermodynamically favored over the cyclization via an ionic pathway, as supported by DFT calculations.