I₂-Promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones: facile and efficient synthesis of 1,4-dihydropyridazines and pyridazines

Abstract

A facile and efficient strategy for the synthesis of 1,4-dihydropyridazines and pyridazines through I2-promoted [4+2] cycloaddition of hydrazones with enaminones has been developed. The switch in selectivity is attributed to...

Recent advances in transition metal-free annulation toward heterocycle diversity based on the C–N bond cleavage of enaminone platform

“…Afterwards, Huang and co-workers employed non-prefunctionalized ketohydrazones to replace the α-halogenated hydrazones in the [4 + 2] cycloaddition and elimination with enaminones to deliver the pyridazines (Scheme 20). 49 A series of 1,4-dihydro pyridazines has been obtained in moderate to excellent yields by heating the reaction mixture at 80 °C in DMSO, while several pyridazines have been afforded by increasing the temperature to 120 °C. In this protocol, the α-halogen hydrazones were generated in situ via iodination of ketohydrazones with I 2 .…”

Emerging Trends in N‐Tosylhydrazone Mediated Transition‐Metal‐Free Reactions

“…Feng et al [85] . developed iodine promoted [4+2] cycloaddition reaction to synthesize pyridazines 57 and 1,4‐dihydropyridazines 59 using enaminones 58 and in situ produced azoalkenes.…”

“…Feng et al [85] developed iodine promoted [4 + 2] cycloaddition reaction to synthesize pyridazines 57 and 1,4dihydropyridazines 59 using enaminones 58 and in situ produced azoalkenes. The produced six-membered heterocycle plays a vital role in pharmaceuticals and natural chemicals ChemistrySelect including hydralazine, antifungal, and antibiotic.…”

Update on the Synthesis of N‐Heterocycles via Cyclization of Hydrazones (2017–2021)

“…[111] In the same year, the group of Huang proposed a method of synthesizing 1,4-dihydropyridazines and pyridazine compounds via cycloaddition of in-situ generated azoolefins 384 and enaminones 385 under metal-free and base-free conditions (Scheme 59c). [6]…”

“…[1,2] Therefore, N-containing heterocyclic compounds have become a focus of organic synthesis research. Thus far, the preparation of nitrogen-containing heterocyclic compounds via methods such as [3 + 2], [3] [3 + 3], [4] [4 + 1], [5] [4 + 2], [6] and [4 + 3] [7] cycloaddition; cross-coupling; [8,9] multicomponent [10] cascade cyclization reactions; etc. has been favored by synthetic chemists and pharmacologists.…”