Table 4. Optimization of the Asymmetric Transfer Hydrogenation of 2-Arylquinoline^a.

entry	catalyst	hydrogen donor	solvent	yield/%b	ee/%c
1	Ir-1	HCOOH	H2O	71	65
2	Ir-2	HCOOH	H2O	65	32
3	Ir-3	HCOOH	H2O	63	54
4	Ir-4	HCOOH	H2O	60	57
5	Ir-5	HCOOH	H2O	54	10
6	Ir-1	HCOOH	CH3OH	68	45
7	Ir-1	HCOOH	CH2Cl2	70	62
8	Ir-1	HCOOH	toluene	54	60
9	Ir-1	HCOOH	MeCN	45	59
10d	Ir-1	HCOOH	H2O	76	59
11e	Ir-1	HCOOH	H2O	80	61
12f	Ir-1	HCOOH	H2O	90	65
13	Ir-1	HCOONa	H2O	<5
14g	Ir-1	HCOOH/HCOONa	H2O	21	61
15f,h	Ir-1	HCOOH	H2O/MeOH	95	66

^aReaction conditions: 1a (0.25 mmol), solvent (2.0 mL), catalyst (1.0 mol %), and hydrogen donor (5.0 equiv) at room temperature under air for 12 h.

^bDetermined by GC–MS using dodecane as the internal standard. The number in the parentheses is the isolated yield.

^cee values were determined by HPLC with an OD-H column.

^dThe reaction was carried out at 40 °C.

^eThe reaction was carried out at 60 °C.

^fThe reaction was carried out with 10.0 equiv of HCOOH.

^gThe reaction was carried out with 5.0 equiv of HCOOH and 2.0 equiv of HCO₂Na.

^hH₂O/MeOH = 1.0/1.0 mL.