Optimization of the reaction conditions^a.

Entry	Ni catalyst	Base	1a : 2a	3ab (%)
1	NiCl2	Na2CO3	1 : 1	nr
2	NiBr2	Na2CO3	1 : 1	36
3	NiSO4	Na2CO3	1 : 1	44
4	(PCy3)2NiCl2	Na2CO3	1 : 1	39
5	(DPPE)NiCl2	Na2CO3	1 : 1	55
6	(PPh3)2NiCl2	Na2CO3	1 : 1	30
7	Ni(CO)4	Cs2CO3	1 : 1	77
8	Ni(CO)4	NaOH	1 : 1	65
9	Ni(CO)4	Na2SO4	1 : 1	50
10	Ni(CO)4	NaOEt	1 : 1	54
11	Ni(CO)4	NEt3	1 : 1	46
12	Ni(CO)4	NaOEt	1 : 1.2	83
13	Ni(CO)4	NaOEt	1 : 1.2	68c
14	Ni(CO)4	NaOEt	1 : 1.2	75d
15	Ni(CO)4	NaOEt	1 : 1.2	73e
16	Ni(CO)4	NaOEt	1 : 1.2	54f

^aUnless otherwise noted, reaction conditions were 1a (0.5 mmol), 2a (0.5 mmol), nickel catalyst (10 mol%), base (2 equiv.), DMSO (5 mL), 90 °C, and a reaction time of 10 h.

^bIsolated yield.

^cAt 80 °C.

^dAt 100 °C.

^eIn CHCl₃.

^fIn DMF.