Table 2. Optimization of the Reaction Conditions^a.

entry	catalyst	solvent	additive	t (days)	yield of 3aa (%)b	ee of 3aac
1	V	CH2Cl2		3	37	77
2	V	CHCl3		4	33	77
3	V	Cl CH2CH2Cl		3	42	61
4	V	CCl4		3	49	49
5	V	Et2O		2	43	64
6	V	toluene		2	58	54
7	V	CH2Cl2	MS (5 Å)d	4	43	69
8	V	CH2Cl2	CF3CH2OHe	4	47	69
9	V	CH2Cl2	K2CO3e	3	39	0
10	V	CH2Cl2	PhCO2Hf	5
11g	V	CH2Cl2		3	44	71
12h	V	CH2Cl2		3	46	67
13	V	CH2Cl2		5	46	74
14	VI	CH2Cl2		4	52	76
15	VI	CH2Cl2		5	61	74
16	IX	CH2Cl2		3	51	74
17	IX	CH2Cl2		5	46	77

^aReaction conditions: 0.1 mmol of 1a, 0.1 mmol of 2a, 5 mol % of catalyst in 1 mL of solvent at rt.

^bIsolated yield of 3aa.

^cDetermined by chiral HPLC.

^d50 mg of MS 5 Å.

^e0.1 mmol of additive was used.

^f0.025 mmol of PhCO₂H was used.

^g0.12 mmol of 1a.

^h0.12 mmol of 2a.