Table 2. Screening bisphosphine ligands for asymmetric hydrogenation of 2-phenylbenzo[b]thiophene 1,1-dioxide 1a ^a .

Entry	Ligand	Conv. b [%]	ee c [%]
1	ZhaoPhos L1	>99	>99
2	L2	>99	>99
3	L3	73	56
4	L4	NR	NA
5 d	ZhaoPhos L1	81	96
6 d	L2	95	98

^aUnless otherwise mentioned, all reactions were carried out with a [Rh(NBD)₂]BF₄/ligand/substrate 1a (0.1 mmol) ratio of 1 : 1.1 : 100 in 1.0 mL CF₃CH₂OH under 50 atm H₂ at 70 °C for 40 h, and the catalyst was pre-complexed in CH₂Cl₂ (0.1 mL for each reaction vial).

^bDetermined by ¹H NMR analysis.

^cThe ee value was determined by HPLC on a chiral phase.

^dCatalyst loading is 0.5 mol%, 12 h. NR = no reaction, NA = not available.