Table 1. Screening of Reaction Conditions^a.

entry	solvent	light source	yield of 3a (%)b	d.r.b
1	acetonitrile	CFL	25	>25:1
2	methanol	CFL	14	>25:1
3	tetrahydrofuran	CFL	29	>25:1
4	ethyl acetate	CFL	17	>25:1
5	dichloromethane	CFL	40	>25:1
6	1,2-dichloroethane	CFL	41	>25:1
7	1,2-dimethoxyethane	CFL	32	>25:1
8	1,4-dioxane	CFL	65	>25:1
9	1,4-dioxane	CFL	30c	>25:1
10	1,4-dioxane	CFL	0d	–
11	1,4-dioxane	CFL	12e	>25:1
12	1,4-dioxane	CFL	37f	>25:1
13	1,4-dioxane/water (2:1)	CFL	47f	>25:1
14	1,4-dioxane	blue LED	23	>25:1
15	1,4-dioxane	CFL	68g	>25:1
16	1,4-dioxane	CFL	73h	>25:1
17	1,4-dioxane	UV-CFL	30	>25:1
18	1,4-dioxane	–	0i	–
19	1,4-dioxane	blue LED	60h,j	>25:1

^aReaction conditions: 1a (0.7 mmol) and 2a (0.1 mmol) in 3 mL of solvent irradiated with two 15 W compact fluorescent lamps in room temperature for 4 h.

^bDetermined by NMR with 1,2,4,5-tetramethylbenzene as internal standard.

^c4 equiv of amine.

^dUnder Ar.

^eUnder O₂.

^fK₂S₂O₈ (2 equiv) used as an additive.

^gAcetic acid (30 equiv) used as additive.

^hAcetic acid (80 equiv) used as additive.

ⁱReaction performed in absence of light.

^jReaction time of 12 h.