Table 1 Optimization of reaction conditions^a

entry	[Co]	solvent	additive	yield (%)^b	dr (cis-3aa/trans-3aa)^c	ee of cis-3aa (%)^c
1	Co-1	TFE	CsOAc	95	10:90	–
2	Co-2	TFE	CsOAc	67	43:57	–
3	Co-3	TFE	CsOAc	94	18:82	–
4^d	(R_a)-Co-4	TFE	CsOAc	10	80:20	69
5	(R_a)-Co-5	TFE	CsOAc	12	90:10	>99
6	(R_a)-Co-6	TFE	CsOAc	19	93:7	>99
7	(R_a)-Co-7	TFE	CsOAc	25	95:5	>99
8	(R_a)-Co-7	TFE	CsOPiv	39	96:4	>99
9	(R_a)-Co-7	TFE	NaOPiv	60	96:4	>99
10	(R_a)-Co-7	TFE	HOPiv	59	92:8	>99
11	(R_a)-Co-7	HFIP	NaOPiv	98	93:7	98
12	(R_a)-Co-7	TFE/HFIP (v/v = 1:1)	NaOPiv	98	94:6	99
13	(R_a)-Co-7	TFE/HFIP (v/v = 3:1)^e	NaOPiv	98	95:5	>99
14	(R_a)-Rh-1	TFE/HFIP (v/v = 3:1)^e	NaOPiv	ND	–	–

^aReaction conditions: 1a (0.05 mmol), 2a (0.075 mmol), [Co] (5 mol%), additive (30 mol%) in solvent (0.3 mL) at 50 °C for 18 h.
^bCombined yield of cis-3aa and trans-3aa.
^cThe ratio of cis-3aa/trans-3aa and the ee value of cis-3aa were determined by HPLC with a chiral stationary phase.
^dAt 80 °C for 10 h.
^eTFE (0.3 mL) and HFIP (0.1 mL) were used as the solvent. ND = not detected.

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