Table 1.

Condition optimization.

Entrya	Rh(II)	Solvent	Yield (%)b	Ee (%)c
1	Rh2(S-TCPTTL)4	DCM	91	60
2	Rh2(S-TCPTTL)4	DCE	90	63
3	Rh2(S-TCPTTL)4	Toluene	85	75
4	Rh2(S-TCPTTL)4	Hexane	90	62
5	Rh2(S-TCPTTL)4	TBME	92	82
6d	Rh2(S-TCPTTL)4	TBME	80	81
7d	Rh2(S-PTTL)4	TBME	82	15
8	Rh2(S-NTTL)4	TBME	90	65
9	Rh2(S-TBPTTL)4	TBME	92	70
10	Rh2(S-TFPTTL)4	TBME	90	99
11	Rh2(S-PTPA)4	TBME	75	5
12	Rh2(S-PTA)4	TBME	72	2
13	Rh2(S-DOSP)4	TBME	90	13
14d	Rh2(S-PTAD)4	TBME	92	25

DCM dichloromethane, DCE 1,2-dichloroethane, TBME tert-butyl methyl ether.

^aThe reaction was carried out on a 0.2 mmol scale: 1a (0.2 mmol), and 4 Å MS (100 mg) in 1.0 mL solvent, was added a solution the catalyst in 1.0 mL of the same solvent via syringe pump in 40 min under inert atmosphere.

^bIsolated yields.

^cDetermined by chiral HPLC analysis, see SI for details.

^dThe reaction was conducted at 0 °C for 24 h.