Optimization of the reaction conditions^a.

Entry	[Cu]	Base	Yieldb (%)
1	Cu	K2CO3	40
2	CuCl	K2CO3	72
3	CuBr	K2CO3	75
4	CuI	K 2 CO 3	82
5	Cu2O	K2CO3	65c
6	CuCl2	K2CO3	63
7	CuO	K2CO3	60
8	CuSO4	K2CO3	54
9	Cu(OAc)2	K2CO3	65
10	—	K2CO3	0d
11	CuI	Na2CO3	54
12	CuI	Cs2CO3	38
13	CuI	K3PO4	46

^aReaction condition: 1 (0.5 mmol), 2b (1 mmol), catalyst (0.05 mmol), base (1.25 mmol), DMSO (2 mL), 80 °C, 16 h in a Schlenk tube under nitrogen atmosphere.

^bIsolated yield.

^cCu₂O (0.025 mmol).

^dIn the absence of catalyst. DMSO = dimethylsulfoxide.