Visible-Light-Promoted Direct Amination of Phenols via Oxidative Cross-Dehydrogenative Coupling Reaction

Abstract

A transition-metal-free approach was disclosed for intermolecular aryl C-N bonds formation between phenols and cyclic anilines via cross-dehydrogenative coupling (CDC) amination that was mediated by visible light, wherein K2S2O8 served as an external oxidant. The salient features of this protocol include circumventing the requirement for prefunctionalized starting materials and achieving single regioselectivity of amination adducts at room temperature.

Visible‐Light‐Promoted Copper‐Catalyzed Regioselective Benzylation of Pyridine N‐Oxides versus Thermal Acylation Reaction with Toluene Derivatives

“…Initially, a metallation reaction occurs preferentially at the C2‐position of the pyridine N ‐oxide derivatives that leads to the formation of intermediate B . Radical intermediate A is generated in situ by hydrogen‐atom abstraction from toluene or benzaldehyde produced by toluene oxidation under the reaction conditions facilitated by the sulfate radical anion that is produced from K 2 S 2 O 8 . Next, coordination of copper complex B with radical A gives intermediate C , which undergoes reductive elimination to afford final product 3 or 4 .…”

“…The general procedure was followed by using quinoline N-oxide (1 mmol, 145 mg), K 2 S 2 O 8 (1.25 mmol, 338 mg), CuO (12 mg, 15 mol-%), p-Xylene (3 mmol, 0.37 mL), and acetonitrile (2 mL 1,138.4,138.3,137.3,135.2,130.7,129.4,128.8,128.7,127.9,122.7,111.9,116.1,43.5,23.3 ppm. MS (EI): m/z (%) = 249 (10) [M] + , 219 (15), 163 (59), 149 (23), 120 (35), 106 (100), 91 (29), 77 (25), 65 (14), 51 (14), 43 (59). C 17 H 15 NO (249.31): calcd.…”

“…The general procedure was followed by using pyridine N-oxide (0.5 mmol, 47 mg), K 2 S 2 O 8 (1.25 mmol, 338 mg), Cu(OAc) 2 (14 mg, 15 mol-%), 2-methylanisole (1.5 mmol, 0.19 mL), and chlorobenzene (2 mL 2,159.7,151.1,138.4,135.9,135.2,130.8,128.1,127.5,125.2,121.4,111.7,56.4 ppm. MS (EI): m/z (%) = 229 (10) [M] + , 198 (88), 170 (18), 135 (14), 106 (66), 78 (100), 51 (29). C 13 H 11 NO 3 (229.23): calcd.…”

“…Radical intermediate A is generated in situ by hydrogen-atom abstraction from toluene or benzaldehyde produced by toluene oxidation under the reaction conditions [28] facilitated by the sulfate radical anion that is produced from K 2 S 2 O 8 . [29] Next, coordination of copper complex B with radical A gives intermediate C, which undergoes reductive elimination to afford final product 3 or 4. To prove the radical mechanism, a control reaction that involves the use of 2,6-di-tert-butyl-4-methylphenol as a radical scavenger was performed.…”

Intermolecular Aryl C−H Amination through Sequential Iron and Copper Catalysis

“…To circumvent prefunctionalisation or preoxidation of either partner, new methods for direct intermolecular dehydrogenative coupling of aryl C−H bonds with non‐activated amines have recently been reported . For example, highly regioselective intermolecular ortho ‐amination through transition‐metal‐catalysed chelation‐directed aryl C−H activation under oxidative conditions has been developed for efficient C−N bond formation (Figure a) . Procedures for directed aryl C−H and N−H bond coupling at more distal positions are less well established.…”