Teaching Old Compounds New Tricks: DDQ‐Photocatalyzed C−H Amination of Arenes with Carbamates, Urea, and N‐Heterocycles

Abstract

The C−H amination of benzene derivatives was achieved using DDQ as photocatalyst and BocNH2 as the amine source under aerobic conditions and visible light irradiation. Electron‐deficient and electron‐rich benzenes react as substrates with moderate to good product yields. The amine scope of the reaction comprises Boc‐amine, carbamates, pyrazoles, sulfonimides and urea. Preliminary mechanistic investigations indicate arene oxidation by the triplet of DDQ to radical cations with different electrophilicity and a charge transfer complex between the amine and DDQ as intermediate of the reaction.

A Retrosynthetic Approach for Photocatalysis

“…Again, this procedure was expanded by Zhou and co‐workers using a cobalt‐based cocatalyst so that no oxygen was required . Finally, our group reported the addition of amides to electron‐deficient arenes complementing the previously mentioned procedures …”

Synthetische Photoelektrochemie

“…One way that researchers overcame this limitation was by employing DDQ, which forms a very powerful excited triplet state (+3.18 V vs. SCE) that can engage unactivated or electrondeficient arenes. 42,43 Photocatalytically-generated arene radical cations can be intercepted by nucleophiles such as 5 to give aminated arenes such as 6 as demonstrated by König ( 10.1002/anie.201913767…”

Electrophotocatalytic SNAr Reactions of Unactivated Aryl Fluorides at Ambient Temperature and Without Base

“…Despite extensive screening, we were unable to achieve higher yields with catalyst 13 . Alternatively, 2,3‐dichloro‐5,6‐dicyanoquinone (DDQ, 14 ), which has a similar excited state reduction potential, has also been used for arene photooxidations . Using 10 mol % DDQ and blue light‐emitting diodes (LEDs) but otherwise identical conditions, the product 12 was generated in 60 % yield.…”

“…Despite extensive screening, we were unable to achieve higher yields with catalyst 13.Alternatively,2,3-dichloro-5,6dicyanoquinone (DDQ, 14), which has asimilar excited state reduction potential, [20][21][22][23][24][25][26] has also been used for arene photooxidations. [23] Using 10 mol %D DQ and blue light-emitting diodes (LEDs) but otherwise identical conditions,the product 12 was generated in 60 %y ield. Theu se of less LiClO 4 was detrimental (entry 3), but other electrolytes were more effective (entries 4a nd 5), with one equivalent of tetrabutylammonium tetrafluoroborate (TBABF 4 )showing the highest efficiency (entry 5).…”

“…To illustrate the applicability of this method to the synthesis of more complex molecules,w ea lso synthesized the products shown in entries 22-28. Thus, av ariety of halogenated purines (entries [22][23][24][25], as teroidal ester-fused pyrazole (entry 26), and a-aminoester-fused pyrazoles (entries 27 and 28) could be N-arylated. Notably,t he ester moieties of adducts 40-42 are representative of functional groups that could be labile under the strongly basic conditions of classic S N Ar reactions,but which are compatible with the current method.…”