Screening of catalysts and reaction conditions^a,b,c.

Entry	R	Catalyst	Solvent	T [°C]	%Yield	ee%
1	Me	Cat. 1	DCM	−78	88	39
2	Me	Cat. 2	DCM	−78	87	42
3	Me	Cat. 3	DCM	−78	89	45
4	Me	Cat. 4	DCM	−78	94	66
5	Me	Cat. 5	DCM	−78	94	45
6	Me	Cat. 6	DCM	−78	90	67
7	Me	Cat. 7	DCM	−78	90	78
8	Me	Cat. 8	DCM	−78	90	21
9	Me	Cat. 9	DCM	0	0
10	Me	Cat. 10	DCM	0	0
11	t Bu	Cat. 7	DCM	−78	46	90
12	t Bu	Cat. 7	DCM	−20	56	95
13	t Bu	Cat. 7	DCM	−50	64	97
14	t Bu	Cat. 7	Hexane	−50	46	93
15	t Bu	Cat. 7	TBME	−50	53	93
16	t Bu	Cat. 7	Toluene	−50	80	99

^aReactions were conducted with 1a or 1b (0.1 mmol) and the catalyst (2 mol%) in 2 ml solvent under Ar.

^bIsolated yields.

^cDetermined by HPLC analysis.