Optimization of the reaction conditions^a.

Entry	Metal salt	Ligand	Yieldb (%)	drc	eed (%)
1	Sc(OTf)3	L3-PiMe3	48	>19 : 1	25
2	Mg(OTf)2	L3-PiMe3	80	>19 : 1	77
3	Ni(OTf)2	L3-PiMe3	85	>19 : 1	80
4	Ni(NTf2)2	L3-PiMe3	87	>19 : 1	80
5	Ni(BF4)2·6H2O	L3-PiMe3	86	>19 : 1	83
6	Ni(BF4)2·6H2O	L3-PrMe3	80	>19 : 1	82
7	Ni(BF4)2·6H2O	L3-RaMe3	76	>19 : 1	70
8	Ni(BF4)2·6H2O	L3-PiMe2	84	>19 : 1	86
9	Ni(BF4)2·6H2O	L3-PiEt2	88	>19 : 1	91
10	Ni(BF4)2·6H2O	L3-PiPr2	95	>19 : 1	71
11e	Ni(BF4)2·6H2O	L3-PiEt2	95	>19 : 1	92
12e,f	Ni(BF4)2·6H2O	L3-PiEt2	86	>19 : 1	92

^aUnless otherwise noted, all the reactions were carried out with 1a (0.10 mmol), 2a (0.10 mmol) and metal salt/ligand (1 : 1, 10 mol%) in CH₂Cl₂ (1.0 mL) at 30 °C for 24 h.

^bIsolated yield of 3aa.

^cDetermined by ¹H NMR.

^dDetermined by HPLC analysis on a chiral stationary phase.

^e 2a (2.0 equiv.) was used.

^f5 mol% catalyst loading.