Screening additive and temperature^a.

Entry	Additive	T (°C)	Yieldb (%)	drc (anti/syn)	eec (%)
1	4-NO2PhCOOH	rt	98	97 : 3	94
2	PhCOOH	rt	98	96 : 4	95
3	CF3OOH	rt	96	96 : 4	93
4	CH3OOH	rt	95	95 : 5	94
5	HCOOH	rt	96	95 : 5	93
6	—	rt	95	98 : 2	95
7	—	10	95	98 : 2	95
8	—	0	93	98 : 2	96
9d	—	0	98	98 : 2	96

^aReaction conditions: p-nitrobenzaldehyde (0.5 mmol), cyclohexanone (10 equiv.), catalyst 1d (0.05 mmol, 10 mol%), solvent (1.0 mL), room temperature, 36 hours with vigorous stirring.

^bCombined yields of isolated.

^cDetermined by HPLC with a chiral AD-H column.

^dVigorous stirring for 48 hours.