Table 1.

Optimization for Rh(III)-catalyzed DKR-ATH of 1a^a

entry	catalyst	Hydrogen donor	Solvent	conv. (%)	eeanti (%)	eesyn (%)	dr (anti/syn)
1	(R,R)-cat.1	HCO2H:Et3N (5:2)	MeOH	<5	–	–	–
2	(S,S)-cat.2	HCO2H:Et3N (5:2)	MeOH	<5	–	–	–
3	(S,S)-cat.3	HCO2H:Et3N (5:2)	MeOH	23	84	–	84:16
4	(R,R)-cat.4	HCO2H:Et3N (5:2)	MeOH	99	−96	–	90:10
5	(R,R)-cat.5	HCO2H:Et3N (5:2)	MeOH	90	−95	–	92:8
6	(R,R)-cat.6	HCO2H:Et3N (5:2)	MeOH	84	−96	–	95:5
7	(S,S)-cat.6	HCO2H:Et3N (5:2)	MeOH	85	96	–	95:5
8	(S,S)-cat.6	HCO2H:Et3N (5:2)	hexane	<5	–	–	–
9	(S,S)-cat.6	HCO2H:Et3N (5:2)	EtOH	71	93	–	97:3
10	(S,S)-cat.6	HCO2H:Et3N (5:2)	DCM	66	95	–	93:7
11	(S,S)-cat.6	HCO2H:Et3N (5:2)	THF	81	99	–	96:4
12	(S,S)-cat.6	HCO2H:Et3N (5:2)	dioxane	97	99	–	93:7
13	(S,S)-cat.6	HCO2H:Et3N (5:2)	toluene	>99	95	–	98:2
14	(S,S)-cat.6	HCO2H:Et3N (5:2)	EtOAc	>99	99	–	98:2
15b	(S,S)-cat.6	HCO2H:Et3N (2:0.02)	EtOAc	>99	–	96	2:98
16c	(S,S)-cat.6	HCO2H:Et3N (2:0)	EtOAc	>99	–	93	<1:99
17d	(S,S)-cat.6	iPrOH	iPrOH	<5	–	–	–
18e	(S,S)-cat.6	HCO2Na	iPrOH	<5	–	–	–

^aConditions: Catalyst/1a (0.1 mmol) ratio of 1:50 in 1 mL of solvent, HCO₂H/Et₃N azeotropic mixture (20 μL) at 25 °C for 12 h. Conversions (conv.) were determined by ¹H NMR analysis. Enantiomeric excesses (ee) and diastereomeric ratios (dr) were determined by HPLC analysis using a chiral stationary phase.

^bHCO₂H (2.0 equiv.) was used.

^cHCO₂H (2.0 equiv.) was used for 48 h.

^dKO^tBu (3.0 equiv.) was used in 1.0 mL of ⁱPrOH at 60 °C for 12 h.

^eHCO₂Na (5.0 equiv.) was used in 2.0 mL of ⁱPrOH /H₂O (1.0 mL/1.0 mL) at 60 °C for 12 h.