Table 1 Condition optimization.

Entry^a	NHC	Base	Solvent	Yield (%)^b	ee (%)^c
1^d	A	K₂CO₃	DCM	nr	–
2^e	A	K₂CO₃	DCM	nr	–
3	A	K₂CO₃	DCM	75	–
4	B	K₂CO₃	DCM	78	84
5	B	Cs₂CO₃	DCM	72	79
6	B	DBU	DCM	70	22
7	B	NaOAc	DCM	Trace	–
8	B	Et₃N	DCM	Trace	–
9	B	DIPEA	DCM	Trace	–
10	B	DABCO	DCM	77	84
11	B	KHCO₃	DCM	81	83
12	B	K₃PO₄	DCM	52	79
13	B	K₂CO₃	THF	Trace	–
14	B	K₂CO₃	DCE	63	87
15	B	K₂CO₃	CHCl₃	75	69
16	B	K₂CO₃	1,4-Dioxane	Trace	–
17^f	B	K₂CO₃	DCM	80	89
18^g	B	K₂CO₃	DCM	89	93
19^h	B	K₂CO₃	DCM	85	95
20^h,i	B	K₂CO₃	DCM	82	93
21^h,j	B	K₂CO₃	DCM	80	92
22^h	C	K₂CO₃	DCM	84	9
23^h	–	K₂CO₃	DCM	nr	–

nr no reaction.
^aStandard condition: 1c (0.1 mmol), 2a (1.5 equiv.), NHC precursor (20 mol %), base (1.5 equiv.), solvent (0.1 M), 30 °C, N₂, 12–72 h.
^bYield (after SiO₂ chromatography purification) were based on 1a.
^cDetermined via chiral phase HPLC analysis.
^d1a was used.
^e1b was used.
^f0 °C.
^g−20 °C.
^h−30 °C.
ⁱNHC precursor (15 mol %).
^jNHC precursor (10 mol %).

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