TABLE 1.

Screening of Solvents and Oxidants^a

entry	solvent	reoxidant	3a (%)
1	t-BuOH	Cu(OAc)2	6
2	t-AmOH	Cu(OAc)2	< 3
3	toluene	Cu(OAc)2	< 3
4	DMSO	Cu(OAc)2	11
5	AcOH	Cu(OAc)2	4
6	DMF	Cu(OAc)2	18
7	DMA	Cu(OAc)2	18
8	NMP	Cu(OAc)2	14
9	dioxane	Cu(OAc)2	< 3
10	DMF/DMSO = 20/1	Cu(OAc)2	9
11	DMF/AcOH = 4/1	Cu(OAc)2	< 3
12	DMF/AcOH/DMSO = 20/5/1	Cu(OAc)2	15
13	DMF/H2O = 9/1	Cu(OAc)2	15
14	MeCN	Cu(OAc)2	9
15	DMF	Cu(OTf)2	11
16	DMF	duroquinone	< 3
17	DMF	PhCO3t-Bub	< 3
18	DMF	Ag2O	< 3
19	DMF	AgOAc	15
20	DMF	O2c	0
21	DMSO	O2c	0
22	DMF	Cu(OAc)2b + Ag2Ob	16
23	DMF	Cu(OAc)2b + air	8
24	DMF	Cu(OAc)2b + O2c	8
25	DMF	CuCl2	18
26	DMF	CuCl2b + O2c	15

^aReaction conditions unless otherwise specified: 1 (0.2 M), 2a (2 equiv), Pd(OAc)₂ (10 mol%), reoxidant (2 equiv) under N₂ at 60 °C for 20 h, the yield was determined by ¹H NMR analysis of the crude product using Ph₃SiMe (1 equiv) as the internal standard. (PMP = p-methoxyphenyl)

^b1 equiv.

^cballon pressure.