Photoredox Cyanomethylation of Indoles: Catalyst Modification and Mechanism

Abstract

The direct cyanomethylation of indoles at the 2- or 3-position was achieved via photoredox catalysis. The versatile nitrile synthon is introduced as a radical generated from bromoacetonitrile, a photocatalyst, and blue LED as a light source. The mechanism of the reaction is explored by determination of the Stern-Volmer quenching constants. By combining photophysical data and mass spectrometry to follow the catalyst decomposition, the catalyst ligands were tuned to enable synthetically useful yields of radical coupling products. A range of indole substrates with alkyl, aryl, halogen, ester, and ether functional groups participate in the reaction, affording products in 16-90% yields. The reaction allows the rapid construction of synthetically useful cyanomethylindoles, products that otherwise require several synthetic steps.

Organic semiconductor photocatalyst can bifunctionalize arenes and heteroarenes

“…ver the past decade, transition metal complexes (1)(2)(3) and organic dyes (4,5) have been investigated extensively as visible light-absorbing catalysts in a wide range of photoredox transformations (4,6). Nonetheless, their use is restricted on account of incompatibility with strong acidic or basic reaction media (7), strong nucleophiles, electrophiles, or reactive radical intermediates (4) exemplified by fac-Ir(ppy) 3 , which reacts with C(sp 3 ) radicals, leading eventually to catalyst deactivation (8,9). The photophysical properties of organic photocatalysts, such as eosin Y, drastically change with changing pH of the solution (7), and acridinium, triarylpyryliums, and quinolinium dyes are deactivated in the presence of nucleophiles such as amines, acetates, phosphates, or cyanide ions (4,10,11).…”

Application of Plasma Treatment in Preparation of Soybean Oil Factory Sludge Catalyst and Its Application in Selective Catalytic Oxidation (SCO) Denitration

“…This results in a reduction of the manganese oxide on the surface of the final sludge catalyst, and a reduction in the active sites. As a result, the catalytic activity of the catalyst is low [32]. …”

Recent Developments in Photo‐Catalyzed/Promoted Synthesis of Indoles and Their Functionalization: Reactions and Mechanisms

“…Conrad and co‐workers developed a photoredox catalyzed direct cyanoalkylation of indoles at the 2‐position to give functionalized indoles (Scheme 48). [77] As for the reaction mechanism, bromoacetonitrile is reduced to radical anion by excited state Ir (III) * via single‐electron transfer, which is converted to acetonitrile radical 136 and bromide anion by decomposition. Then, electron‐deficient radical 136 reacts with electron‐rich indoles to give radical intermediate 137 .…”