Optimization of the reaction conditions^a.

Entry	Catalyst	Solvent	Yieldb (%)	eec (%)
1	(S)-4.1a	DCE	60	42
2	(S)-4.1b	DCE	73	38
3	(S)-4.1c	DCE	80	66
4	(S)-4.1d	DCE	64	2
5	(S)-4.1e	DCE	81	30
6	(S)-4.1f	DCE	47	18
7	(S)-4.1g	DCE	89	63
8	(S)-4.1h	DCE	71	58
9	(S)-4.1i	DCE	86	72
10	(R)-4.2a	DCE	72	32
11	(R)-4.3a	DCE	75	34
12	(S)-4.1i	DCM	79	64
13	(S)-4.1i	CHCl3	83	64
14	(S)-4.1i	Et2O	59	52
15	(S)-4.1i	EA	74	59
16	(S)-4.1i	1,4-Dioxane	80	32
17d	(S)-4.1i	DCE	86	86
18 e	(S)-4.1i	DCE	88	87
19f	(S)-4.1i	DCE	56	79

^aReaction conditions: 1a (0.05 mmol), 2a (0.06 mmol) and catalyst (10 mol%) in DCE (0.5 mL) at room temperature for 12 h.

^bIsolated yields.

^cDetermined by chiral HPLC analysis.

^d3 Å MS.

^e4 Å MS.

^fAt 0 °C.