An Efficient Route to 3,3′‐Biindolinylidene‐diones by Iron‐Catalyzed Dimerization of Isatins

Abstract

Iron-catalyzed dimerization of various isatin derivatives is described for the efficient synthesis of 3,3'-biindolinylidene-diones (isoindigos). The reaction provides easy access to self-coupled and cross-coupled 3,3'-indolinylidene-diones that have high relevance to biology and materials. This Fe(0)or Fe(II)-catalyzed dimerization reaction tolerates a wide range of functionalities, such as fluoro, chloro, bromo, alkenyl, nitrile, ether, ester, pyrrolyl, indolyl and carbazolyl groups, including cyclic and acyclic alkyls as well as an alkyl-bearing fatty-alcohol moiety. Especially, the coupling between two distinct isatins provided excellent selectivity for the crossdimerization with trace of self-couplings. The single-crystal Xray diffraction study established the molecular structure of eight dimerized products. A preliminary mechanistic study of the Fe-catalyzed dimerization supported the radical pathway for the reaction.

DBU-Mediated Dimerization: Facile Access to 9,9′-Bifluorenylidenes and Isoindigos

“…Knowing the importance of the isoindigo core structure in conjugated polymers (CPs), organic photovoltaics (OPVs), organic field-effect transistors (OFETs) 10 and biologically important molecules, 11 we decided to explore the synthetic utility of the present methodology for the synthesis of isoindigos. On the basis of a literature search, there are a vast number of reported synthetic protocols to construct isoindigos, for example, acid-catalyzed condensation of isatins with oxindoles, 12 gold-catalyzed dimerization of 3-diazooxindoles, 13 palladium-catalyzed cyclization, 14 dimerization of oxindoles using thionyl chloride (SOCl 2 ) 15 or N-chlorosulfenylsuccinimide, 16 sodium iodide promoted dimerization of oxindoles, 17 visible-light-promoted, iodine-mediated dimerization of 3-diazooxindoles, 18 iron-catalyzed dimerization of isatins, 19 and dimerization of indoles promoted by a combination of I 2 /DMSO/K 2 S 2 O 8 . 20 Recently, we disclosed the dimerization of 3-chlorooxindoles by employing potassium ethyl xanthate for the synthesis of a range of isoindigos in yields of 52-89%.…”

Advances in the Iron-Catalyzed Direct Functionalizations of ­Heterocycles

“…Very recently, Punji has developed a Fe-catalyzed protocol to synthesize 3,3'biindolinylidene-2,2'-diones by the self-and cross-dimerization of isatins (Scheme 20). 39 Both the Fe(0) and Fe(II) act as an ideal catalyst for this reaction and afford a range of dimerized products of isatins. The use of PMe3 ligand along with LiHMDS is essential while using Fe(II) salt as a catalyst.…”

Iron-catalyzed selective construction of indole derivatives via oxidative C(sp3)–H functionalization of indolin-2-ones

“…45 Recently, we reported the organocatalyzed self-condensation of 3-thioisatins, in situ generated from COS-triggered oxygen/sulfur exchange of isatins or the sulfuration of 2-oxoindoles with S 8 , to effectively construct a series of structurally diverse isoindigos, along with the generation of undesirable byproducts, such CO 2 or H 2 S. 46,47 Meanwhile, Punji's group further reported iron-catalyzed dimerization of isatins to isoindigos with oxygen as the sole byproduct. 48 In the case of iron-catalyzed oxidative alkylation and hydroxylation of indolin-2-ones reported by Xu's group in 2020, the oxidative product (indoline-2,3-dione) and radical coupled product (3-hydroxy-3,3′-biindoline-2,2′-dione) were detected in the absence of alkyl-substituted N-heteroarenes (Scheme 1(II)). 29 Based on the recent progress on this topic, the multifunctional adjustable properties of iron-catalyzed oxidation of unactivated C(sp 3 )–H bonds prompted us to further expand the scope of iron-catalysis to construct value-added indole derivatives.…”