Table 1. Optimization of reaction conditions ^a .

Entry	Variations from the ‘standard’ conditions	Yield of 3a (%)
1	Without Cu(OPiv)2	Trace
2	Cu(OAc)2 instead of Cu(OPiv)2	17
3	Without MesCOOH	68
4	PivOH instead of MesCOOH	74
5	AgSbF6 (0.5 equiv.)	53
6	AgNTf2 instead of AgSbF6	9
7	80 °C instead of 90 °C	34
8	100 °C instead of 90 °C	74
9	DCE instead of 1,4-DCB	Trace
10	Toluene instead of 1,4-DCB	—
11	[Ir] instead of [Rh]	Trace
12	[Ru] instead of [Rh]	36
13	[Rh] (2.5 mol%)	70
14	2-Butenone (1.0 equiv.)	33
15	2-Butenone (3.0 equiv.)	62
16	Cu(OPiv)2 (1.0 equiv.)	49
17	Cu(OPiv)2 (2.0 equiv.)	71
18	Under air	39

^aReaction conditions: 1a (0.05 mmol) and 2a (0.25 mmol) in 1.5 mL of solvent under argon in a closed flask; 1,4-DCB = 1,4-dichlorobutane; Cu(OPiv)₂ = copper pivalate; AgSbF₆ = silver hexafluoroantimonate(V); MesCOOH = 2,4,6-trimethylbenzoic acid; PivOH = pivalic acid; AgNTf₂ = silver bis(trifluoromethanesulfonyl)imide; DCE = 1,2-dichloroethane; [Ir] = [Cp*IrCl₂]₂; [Ru] = [Ru(p-cymene)Cl₂]₂. Yield determined by ¹H NMR spectroscopy using dibromomethane as an internal standard.