Tandem Organocatalysis and Photocatalysis: An Anthraquinone‐Catalyzed Indole‐C3‐Alkylation/Photooxidation/1,2‐Shift Sequence

Abstract

Quinones exhibit orthogonal ground- and excited-state reactivities and are therefore highly suitable organocatalysts for the development of sequential catalytic processes. Herein, the discovery of an anthraquinone-catalyzed thermal indole-C3-alkylation with benzylamines is described, which can be combined sequentially with a new visible-light-driven catalytic photooxidation/1,2-shift reaction. The one-flask tandem process converts indoles into 3-benzylindole intermediates, which are further transformed into new fluorescent 2,2-disubstituted indoline-3-one derivatives.

Access to 3‐Oxindoles from Allylic Alcohols and Indoles

“…Outer‐sphere approach of nucleophilic indole 1 on π–allylic ruthenium(IV) intermediate II is followed by proton transfer and ligand exchange on IV with allylic alcohol 2 to release allylated indole 3 . Concerning pseudoindoxyls 6 , according to previous reports on the oxidation of 2,3‐disubstituted indoles and related compounds, hydroperoxide A tends to be the key intermediate ,. Homolysis of this hydroperoxide followed by reduction through comproportionation with 3 , water, or the surface involving hydroxy radicals might explain the formation of hydroxyindolenine B .…”

Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides

“…[16,18] Not surprisingly, different quinone derivatives have been used for photo-oxidative transformations under visible light. [19][20][21][22] Fukuzumi reported the photoredox catalytic conversion of benzene to phenol with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) under visible-light irradiation. [23] Itoh and subsequently Yuan reported the trifluoromethylations of arenes and heteroarenes with anthraquinone-2-carboxylic acid [24] and abstraction or C-C bond-forming reactions.…”

Visible‐Light‐Triggered Quantitative Oxidation of 9,10‐Dihydroanthracene to Anthraquinone by O2 under Mild Conditions

“…According to the present results and literature reports, a mechanism of AQ‐photocatalyzed DHA oxidation with O 2 is proposed as follows (Scheme ): On the basis of the UV/Vis spectrum of high concentrations of AQ (Figure S12 in the Supporting Information), AQ can absorb visible light more efficiently than DHA to form its excited state AQ*. Then, this AQ*, which is probably more active than DHA*, directly abstracts one H atom on the 9 or 10 carbon sites of DHA to yield its reduced species ( K ) and the above radical B .…”