... Tetrahedron: Asymmetry. Volume 24, Issue 8, 30 April 2013, Pages 515–525. ... conducted with (S)-proline (20 mol %), thiourea or pyridine derivatives (10–20 mol %), cyclohexanone (16 equiv), p-nitrobenzaldehyde (0.125 mmol) and hexane (2 mL) at room temperature for 24 h. b ...