Pyrrolo[3,4-c]pyrazole Synthesis via Copper(Ι) Chloride-Catalyzed Oxidative Coupling of Hydrazones to Maleimides

Abstract

A variety of pyrrolo­[3,4-c]­pyrazole derivatives from readily available aldehyde hydrazones and maleimides via direct oxidative coupling under radical cascade reaction have been reported. This method offers satisfactory chemical yields and good functional group compatibility. Moreover, this practical approach is catalyzed by CuCl utilizing air as the oxidant and some control experiments were performed to elaborate the mechanism.

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

“…In 2019, Zhao and co-workers revealed a mild CuCl-catalyzed oxidative coupling reaction of hydrazones with maleimides 260 that produces dihydropyrazoles 262, where the addition of bis(trifluoroacetoxy) iodo benzene (BTI) promotes the dehydrogenation aromatization of pyrazoles 261 (Scheme 41). [75] Remarkably, this transformation exhibits excellent tolerance and yields in the presence of electron-with- drawing groups such as bromide, chloride, or fluoride and electron-donating groups such as methyl and methoxy.…”

Iodine-Catalyzed Regioselective Oxidative Cyclization of Aldehyde Hydrazones with Electron-Deficient Olefins for the Synthesis of Mefenpyr-Diethyl

“…In recent years, metal-free catalyzed oxidative C–H functionalization has been gained considerable attention due to its low costs and the formation of environmentally acceptable byproducts. − Molecular iodine, which possesses various oxidation states and mild redox potential, has been widely utilized in oxidative coupling reactions. − Furthermore, the combination of the iodine/peroxide mediated oxidative coupling reactions has been investigated to some extent. − Despite the compelling progress, the examination of direct catalytic transformation via a iodine catalyzed strategy for the construction of privileged heterocyclic compounds is still promising. Inspired by our previous work, − and literature reports, we herein report a I 2 -catalyzed pyrazoles synthesis by an oxidative radical relay strategy.…”

Metal-Free Tandem Oxidative Cyclization for the Synthesis of 1,2-Dihydropyridazines and Pyrazoles

“…β,γ-Unsaturated hydrazones are valuable synthetic building blocks, which could undergo diverse synthetic transformations . The common method to obtain the β,γ-unsaturated hydrazones is allylation of aldehyde, followed by condensation with hydrazines .…”