Table 1.

Reaction optimization.

Entrya	4	Ligand	Solvent	Yield (%)b	d.r.c	e.e. (%)d
1	4a	L1	Toluene	70	93:7	96
2	4b	L1	Toluene	20	87:13	94
3	4c	L1	Toluene	76	92:8	92
4	4d	L1	Toluene	74	67:33	29
5	4e	L1	Toluene	22	71:29	59
6	4f	L1	Toluene	83	50:50	18
7	4a	L2	Toluene	42	60:40	73
8	4a	L3	Toluene	51	>95:5	99
9	4a	L4	Toluene	39	81:19	87
10	4a	L3	DCM	47	>95:5	99
11	4a	L3	THF	79 (77)	>95:5	>99
12	4a	L3	MeOH	22	73:27	84
13	–	L3	THF	n.d.	–	–
14e	4a	–	THF	n.d.	–	–
15	4a	–	THF	<5	–	–

^aReaction conditions: Cu(CH₃CN)₄PF₆ (5 mol%) and pyridine bis(oxazoline) ligand L (10 mol%) were stirred in solvent (0.5 mL) at 25 °C for 1 h, then NHC precatalyst 4 (5 mol%), 1a (0.15 mmol), 2a (0.1 mmol), MeOH (0.5 mmol), Na₂CO₃ (0.1 mmol) and solvent (0.5 mL) were added to the reaction mixture and stirred for 12 h under N_2.

^bThe yield was determined by ¹H NMR spectroscopy (yield of isolated product given within parentheses).

^cThe diastereomeric ratio (d.r.) was determined by ¹H NMR spectroscopy.

^dThe enantiomeric excess (e.e.) was determined by HPLC.

^eIn the absence of Cu(CH₃CN)₄PF₆. Mes = mesityl, DCM = dichloromethane, THF = tetrahydrofuran, n.d. = not detected.