TABLE 1. Optimizing Reaction Conditions.

entry	CuX	solventa	conversion (%)b
1	CuCN	CH2CI2	24
2	CuOAc	CH2CI2	<5
3	Cu(OTf)2	CH2CI2	0
4	Cu(BF4)2	CH2CI2	15
5	Cu(NO3)2	CH2CI2	0
6	Cu(CIO4)2	CH2CI2	22
7	Cu(CF3COO)2	CH2CI2	0
8	Cu(CH3CN)4PF6	CH2CI2	27
9	CuCI	CH2CI2	35
10	CuBr	CH2CI2	43
11	CuI	CH2CI2	64
12	-	CH2CI2	45
13c	CuI	CH2CI2	63
14d	CuI	CH2CI2	68
15	CuI	Toluene	64
16	CuI	THF	70
17	CuI	Et2O	71
18e	CuI	Et2O	76
19f	CuI	Et2O	85
20f	-	Et2O	43
21g	CuI	Et2O	>99 (98)h

^aReaction run in 0.5 m solution.

^bBased on ¹H NMR.

^cUsing 6 mol % CuI.

^dUsing 3 mol % Grubbs-2 and 6 mol % CuI.

^eReaction run in 0.2 m solution.

^fReaction run in 0.1 m solution.

^gAt 35 °C for 3 h; without CuI; yield = 57%

^hIsolated yield.