Investigation of reaction conditions^a.

Entry	[V] catalyst	Ligand	Yield (%)
1	VCl3(thf)3	—	48
2	VBr3(thf)3	—	42
3	VCl3(py)3	—	0
4	VCl2(thf)2	—	60
5	VCl2(1,4-dioxane)2	—	47
6	VI2(thf)4	—	27
7	VCl2(thf)2	dppm	27
8	VCl2(thf)2	dppe	20
9	VCl2(thf)2	2,2′-Bipyridine	0

^aReactions of 1a (0.10 mmol) with 2a (0.20 mmol) in the presence of a catalyst (20 mol%) and a ligand (20 mol%) in toluene (2.0 mL) at 110 °C for 16 h.