trans-4-Hydroxy-l-proline Hydrazide-Trifluoroacetic Acid as Highly Stereoselective Organocatalyst for the Asymmetric Direct Aldol Reaction of Cyclohexanone

Abstract Protonated N′-benzyl-N′-L-prolyl-TRANS-4-hydroxy-L-proline hydrazide has been found to be superior to the L-proline hydrazide counterpart as the catalyst for the asymmetric aldol reaction of cyclohexanone and aromatic aldehydes, resulting in excellent ­diastereoselectivities (up to >99:1 dr) and enantioselectivities (up to >99% ee).