• Caffeine [C2042]
• Tris(2,2'-bipyridyl)ruthenium(II) Chloride Hexahydrate (= Ru(bpy)₃Cl₂?6H₂O) [T1655]
• 4-Methoxybenzenediazonium Tetrafluoroborate [M2636]
• Formic acid [F0513]

Ru(bpy)₃Cl₂?6H₂O (80.1 mg, 0.125 mmol, 2.5 mol%), caffeine (9.71 g, 50.0 mmol, 10 eq.), 4-methoxybenzenediazonium tetrafluoroborate (1.11 g, 5.00 mmol, 1.0 eq.) and formic acid (25 mL) were added to a 100 mL four-necked round bottomed flask at room temperature. The mixture was placed at a distance of 2-3 cm from Blue LED lamps. The brown solution was stirred at rt under visible light irradiation. After 14 hours of irradiation, 5% sodium bicarbonate and dichloromethane were added. The organic layer was washed with brine. Organic layer was dried over Na₂SO₄ and concentrated under reduced pressure to afford the crude product as a red solid (8.20 g), which was purified by column chromatography on silica gel (hexane:ethyl acetate = 80:20 - 34:66) to afford compound 1 as a pale red solid (632 mg, y. 42 %).

The flask was irradiated with 40 W blue LED lamps (3 cm away, with cooling fans to keep the reaction at room temperature).
The reaction mixture was monitored by ¹H NMR.

¹H NMR (400 MHz, CDCl₃); δ 7.62 (d, J = 8.7 Hz, 2H), 7.01 (d, J = 8.7 Hz, 2H), 4.02 (s, 3H), 3.86 (s, 3H), 3.61 (s, 3H), 3.41 (s, 3H).

¹³C NMR (101 MHz, CDCl₃); δ 161.1, 155.5, 152.1, 151.7, 148.2, 130.6, 120.5, 114.3, 108.2, 55.4, 33.9, 29.8, 27.9.

• Direct Arylation of N-Heteroarenes with Aryldiazonium Salts by Photoredox Catalysis in Water
• D. Xue, Z.-H. Jia, C.-J. Zhao, Y.-Y. Zhang, C. Wang, J. Xiao, Chem. Eur. J. 2014, 20, 2960.

• Room-Temperature C–H Arylation: Merger of Pd-Catalyzed C–H Functionalization and Visible-Light Photocatalysis
• D. Kalyani, K. B. McMurtrey, S. R. Neufeldt, M. S. Sanfold, J. Am. Chem. Soc. 2011, 133, 18566.