Optimization of the [2 + 2] cycloaddition^a.

Entry	Deviations from standard conditions	Yield (%)
1	None	>95
2	No photocatalyst	n.d. (>95 rsm)
3	No light	n.d. (>95 rsm)
4	No glycerol	Degradation
5	5 min instead of 10 min	75 (25 rsm)
6	25 equiv. of indole	88
7	50 equiv. of indole	93
8	200 equiv. of indole	67 (19 rsm)
9	MeOH instead of DMSO	15 (68 rsm)
10	DMA instead of DMSO	44
11	Ir(ppy)2(dtbbpy)]PF6	n.d. (71 rsm)
12	Ir(ppy)3	n.d. (70 rsm)
13	[Ir{dF(CF3)ppy}2(bpy)]PF6	83
14	HP-A instead of HP-1	n.d. (71 rsm)

^aStandard conditions: DNA (2 mM in H₂O, 10 nmol, 1 equiv.), 1a (100 mM in DMSO, 100 equiv.), [Ir{dF(CF₃)ppy}₂(dtbbpy)]PF₆ (2 mM in DMSO, 1 equiv.), glycerol (2 μL in 8 μL of DMSO), rt, 10 min, blue Kessil. Work-up: ethanol precipitation. n.d. = product not detected. rsm = recovered starting material.