A 200 mL glass reactor equipped with a magnetic stirring bar was charged with tert-butyl 4oxopiperidine-1-carboxylate (500 mg, 2.5 mmol, 1 eq.), [Ir(dFCF3ppy)2dtbbpy]PF6] 3 (0.05 mmol, 0.02 eq., 56.1 mg), NiBr2 (dtbbpy) 3 (0.25 mmol, 0.1 eq., 121.75 mg and K2HPO4 (0.75 mmol, 0.3 eq., 131 mg). The glass reactor was closed, evacuated, and back filled with N2 for three times before adding anhydrous EtOAc (50.0 ml) into the reaction reactor. All solid compounds were added first to the glass reactor, followed by anhydrous EtOAc (50 ml) under nitrogen atmosphere. The mixture was stirred under light irradiation using a 450 nm (± 15 nm) LED for 30 h at 35 °C using a cryostat (please see Fig. for the reaction set up). The reaction progress was monitored by TLC. After completion of the reaction, the reaction mixture was subjected to purification by silica gel flash column chromatography to isolate the product tert-butyl 4-oxo-3,4-dihydropyridine-1(2H)-carboxylate (376 mg, 76%). a Yields were determined by GC-FID analysis against an internal standard. a Yields were determined by GC-FID analysis against an internal standard. a Yields were determined by GC-FID analysis against an internal standard.