Screening of the reaction conditions^a.

Entry	Catalyst (mol%)	Solvent	Time	Yieldb (%)
				4a	5a
1	pTsOH·H2O (10)	1,2-DCE	10 h	0	52
2	Cu(OTf)2 (10)	1,2-DCE	10 h	48	0
3	CuOTf (10)	1,2-DCE	10 h	60	0
4	Yb(OTf)3 (10)	1,2-DCE	24 h	0	51
5	Zn(OTf)2 (10)	1,2-DCE	24 h	0	53
6	FeCl3·6H2O (10)	1,2-DCE	24 h	0	55
7	HAuCl4·3H2O (10)	1,2-DCE	24 h	0	Trace
8	CuCl (10)	1,2-DCE	24 h	0	0
9	CuBr (10)	1,2-DCE	24 h	0	0
10	CuOAc (10)	1,2-DCE	24 h	0	0
11c	CuOTf (10)	1,2-DCE	24 h	0	0
12d	CuOTf (10)	THF	10 h	31	0
13e	CuOTf (10)	Toluene	10 h	34	0
14e	CuOTf (10)	DMF	10 h	30	0
15	CuOTf (5)	1,2-DCE	10 h	20	0
16	CuOTf (20)	1,2-DCE	10 h	51	0

^aReaction conditions: 1 (0.5 mmol), 2u (0.5 mmol), solvent (5 mL), under air, the reaction was monitored by TLC.

^bYield of the isolated product.

^cReaction was run at 25 °C.

^dReaction was run at 66 °C.

^eReaction was run at 90 °C.