Organocatalyzed aldol reaction of acetone with p-nitrobenzaldehyde^a.

Entry	Cat	T	% convb	10 : 11c	e. r.d
1	4	NO	14	50 : 50	76 : 24
2	6a	NO	58	91 : 9	76 : 24
3	6b	NO	60	100 : 0	88 : 12
4	4	YES	76	83 17	62 : 38
6	6b	YES	78	91 : 9	70 : 30

^aReaction conditions: acetone (0.25 mmol), p-nitrobenzaldehyde (0.025 mmol), catalyst (10 mol%), N-hexylthymine (0 or 0.125 mmol), CH₂Cl₂ (100 μL), 25 °C, 4 days.

^bDetermined by ¹H NMR from the crude reaction.

^cRatio of 10 : 11 was determined by ¹H NMR analysis.

^de. r. determined by HPLC using a Daicel ChiralPak AS-H column.