Table 1 Optimization of the reaction conditions^a


Entry	Variations from standard conditions	Yield of 3aa (%)^b
1	none	94 (91)^c
2	[Ru(bpy)₃](PF₆)₂ instead of 4DPAIPN	36
3	[Ir(ppy)₂(dtbbpy)](PF₆) instead of 4DPAIPN	78
4	[Ir(dF(CF₃)ppy)₂(dtbbpy)](PF₆) instead of 4DPAIPN	54
5	4CzIPN instead of 4DPAIPN	27
6	DMF instead of DMSO	trace
7	MeCN instead of DMSO	49
8	Na₂C₂O₄ or K₂C₂O₄ instead of H₂C₂O₄/TMG	trace
9	(ⁿBu₄N)₂C₂O₄ instead of H₂C₂O₄/TMG	56
10	Et₃N or DIPEA instead of H₂C₂O₄/TMG	0
11	HCO₂H instead of H₂C₂O₄	0
12	green LEDs (λ = 525 nm) instead of blue LEDs	47
13	red LEDs (λ = 640 nm) instead of blue LEDs	0
14	heat to 80 °C in the dark	0
15	no 4DPAIPN	0

LED light-emitting diode, TMG 1,1,3,3-tetramethylguanidine, DIPEAN,N-diisopropylethylamine.
^astandard conditions: 1a (0.2 mmol), 2a (0.5 mmol), H₂C₂O₄ (0.5 mmol), TMG (0.5 mmol), 4DPAIPN (1 mol%), DMSO (2 mL), argon atmosphere, 30 W blue LEDs (λ_max = 456 nm), rt, 90 min.
^byield was determined by ¹H NMR spectroscopy analysis with diphenylacetonitrile (DPA) as an internal standard.
^cisolated yield in parentheses with a 1.17:1 diastereomeric ratio (d.r.).

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