Design of Novel Hydrogen-Bonding Donor Organocatalysts and Their Application to Asymmetric Direct Aldol Reaction

Asymmetric catalytic activities of various organocatalysts bearing double hydrogen-bonding donor units showing different pK a values were examined for direct aldol reactions of cyclohexanone with aromatic aldehydes. Organocatalyst with motif exhibiting the highest acidity resulted in the corresponding aldol products with the highest enantioselectivity. A good correlation has been observed between the asymmetric catalytic activity for direct aldol reactions and acidities of double hydrogen-bonding donating units.