4-trans-Amino-proline based di- and tetrapeptides as organic catalysts for asymmetric C–C bond formation reactions

4-trans-Amino-proline based di- and tetrapeptides have been successfully applied as chiral organocatalysts in the enantioselective conjugate addition of nitroalkanes to cyclic enones and the direct aldol reaction. Two 4-trans-amino-proline residues were shown to be sufficient enough to catalyze the conjugate addition reactions with up to 88% ee and up to 100% yield. It has been demonstrated that 4-trans-amino-proline based di- and tetrapeptides are significantly more active than l-proline (at 30 mol %) and can catalyze the direct aldol reaction with good yield and enantioselectivity within 3 h and at lower catalyst loading (5 mol %).