Table 1.

Optimization of the reaction conditions

				4a		5a
entry	Ligand (L)	Mg(OTf)2: L	T (°C)	Yield (%)a	e.r.b	Yield (%)a	e.r.b
1	L-PrPr 2	1.0:1.0	35	29	82:18	53	92.5:7.5
2	L-PiPr 2	1.0:1.0	35	–	–	97	82:18
3	L-RaPr 2	1.0:1.0	35	38	83.5:16.5	46	96:4
4	L-RaPr 3	1.0:1.0	35	36	72:28	43	86.5:13.5
5	L-RaPr 2	1.5:1.0	35	–	–	88	94:6
6	L-RaPr 2	1.0:1.5	35	53	88:12	25	95.5:4.5
7c	L-RaPr 2	1.4:1.0	30	–	–	91	94.5:5.5
8d	L-RaPr 2	1.0:1.5	−40	57	94.5:5.5	–	–
9d,e	L-RaPr 2	1.0:1.5	−40	73	95:5	–	–
10f	L-RaPr 2	1.0:1.5	−40 then −20	91	95:5	–	–

Unless otherwise noted, all reactions were carried out with 1a (0.10 mmol), 2a (0.12 mmol), 3a (0.10 mmol), and Mg(OTf)₂/L-RaPr₂ (1.0:1.0, 10 mol%) in CH₂Cl₂ (1.0 mL) at 35 °C for 3 h

^aIsolated yield

^bDetermined by CSP-HPLC analysis

^cCarried out with 1a (0.20 mmol), 2a (0.24 mmol), 3a (0.20 mmol), and Mg(OTf)₂/L-RaPr₂ (1.4:1.0, 10 mol%) in CH₂ClCH₂Cl (1.0 mL) at 30 °C for 3 h

^d−40 °C for 7 days

^eWith 5 Å MS (10 mg) as the additive

^fCarried out with 1a (0.10 mmol), 2a (0.15 mmol), 3a (0.15 mmol), 5 Å MS (10 mg), and Mg(OTf)₂/L-RaPr₂ (1.0/1.5, 10 mol%) in CH₂Cl₂ (1.0 mL) at −40 °C for 2 days, then −20 °C for 3 days