Table 1. Reaction Optimization.

no.a	solvent	4a:5a ratio	other	yield (%)
1	toluene	1:2		50
2	n-hexane	1:2		24
3	CHCl3	1:2		68
4	DCM	1:2		80
5	1,2-DCE	1:2		73
6	EtOAc	1:2		67
7	CH3CN	1:2		69
8	THF	1:2		67
9	DCM	1:4		60
10	DCM	1:1		76
11	DCM	2:1		55
12b	DCM	1:2	slow add.	83
13	DCM	1:2	0.5 mL	76
14	DCM	1:2	2 mL	71
15c	DCM	1:2	dark	no reaction

^aReaction conditions: 4a (0.4 mmol) and 5a (0.8 mmol) were dissolved in 1 mL of solvent and were irradiated at room temperature with blue LEDs (1 W, 470 nm) overnight (16 h).

^b4a and 5a were each dissolved in 0.5 mL of DCM, 5a being slowly added over the course of 6 h by a syringe pump, under otherwise identical conditions.

^cThe reaction mixture was stirred in the dark.