Oxidative cross-coupling of quinoxalinones with indoles enabled by acidochromism

Abstract

An oxidative cross-coupling of quinoxalinones with indole derivatives by B(C6F5)3.H2O induced acidochromism of quinoxalinone derivatives was developed under mild and external photocatalyst-free conditions. The reaction enjoys excellent substrate scope accommodating...

Mild Iron-Catalyzed Oxidative Cross-Coupling of Quinoxalinones with Indoles

“…This is a known structure. These data are similar to the reported ones [17]. 1-allyl-3-(1H-indol-3-yl)quinoxalin-2(1H)-one (3s): Isolated through silica gel column chromatography with ethyl acetate and petrol ether (1:4) to produce orange solid.…”

“…Based on the aforementioned findings and the relevant literature [ 14 , 17 ], we propose a plausible mechanism for the transformation of quinoxalinones ( 1 ) with indoles ( 2 ) to afford a variety of 3-(indol-3-yl)quinoxalinones ( 3 ), as illustrated in Scheme 4 . Initially, quinoxalinone ( 1a ) is coordinated to the Lewis acid (FeCl 3 ), resulting in the formation of a cationic intermediate.…”

“…Notably, 4a could be further oxidized to the desired product 3a in a 63% yield upon continuation of the reaction under the standard condition. This observation implies that a Lewis acid-catalyzed Friedel–Crafts-type reaction is likely the initial step, leading to the formation of intermediate 4a [ 14 , 17 ]. Furthermore, the observed lower efficiency with electron-deficient indoles ( Figure 1 , entries featuring 5-nitro- 1H -indole and 1H -indole-5- carbonitrile) provides additional support for the proposed iron salt-catalyzed Friedel–Crafts-type electrophilic substitution reaction mechanism.…”

“…Molecular iodine has also proven effective for this reaction [ 15 ]. With the advent of electrochemistry and photochemistry, these innovative methodologies have been integrated into the reaction system [ 16 , 17 , 18 ]. For instance, Tang’s group has reported a visible light-promoted cross-coupling of quinoxalinones with indole derivatives, utilizing B(C 6 F 5 ) 3 ·H 2 O as a Lewis acid catalyst ( Scheme 1 A) [ 17 ].…”

Discovery of the Quinoxalinone–B(C6F5)3·H2O Combo as a Photocatalyst by Acidochromism Strategy: Aerobic Oxidation of Alcohol, Alkene, and Thiols

“…The unique chemical property of acidochromic units is their ability to transform from colorless to colored states upon the addition of a certain acid . Such a property offers a potential way to facilitate photoexcitation with visible light, even though the starting molecules are not sensitive by visible light irradiation …”