Table 1.

Optimized conditions for the reaction^a.

Entry	Catalyst	Ligand	Solvent	Additives	t (h)	Yield (%)b	Ee (%)c
1	AgOTf	L1	DCE	–	0.5	70	29
2	CuBF4	L1	DCE	–	72	50	36
3	CuCl	L1	DCE	–	72	51	73
4	CuCl	L1	THF	–	72	38	69
5	CuCl	L1	MeCN	–	72	34	56
6	CuCl	L1	Toluene	–	72	45	76
7	CuCl	L2	Toluene	–	72	30	20
8	CuCl	L3	Toluene	–	72	35	46
9	CuCl	L4	Toluene	–	72	56	69
10	CuCl	L5	Toluene	–	72	30	35
11d	CuCl	L1	Toluene	–	72	51	90
12d	CuCl	L1	Toluene (2.0 mL)	–	72	70	90
13d	CuCl	L1	Toluene (3.0 mL)	–	72	58	90
14d	CuCl	L1	Toluene	(R)-CPA	36	88	92
15d	CuCl	L1	Toluene	TsOH	36	67	90
16d	CuCl	L1	Toluene	PhCOOH	36	57	90
17d	CuCl	L1	Toluene	(R)-CPA (0.5 eq)	36	83	91
18d	CuCl	L1	Toluene	(R)-CPA (0.2 eq)	36	76	90
19d	CuCl	L1	Toluene	NaBArF	72	26	13
20d	CuCl	L1	Toluene	DBU	72	N.D.e	N.D.e

^aReaction conditions: 1a (0.1 mmol), catalyst (10 mol%), ligand (15 mol%), solvent (1.0 mL), 20 °C.

^bYields of isolated products.

^cEe values were determined by chiral HPLC.

^d1b was used as the substrate.

^eN.D. = Not detected. Compound 1b was decomposed.