Dimers Derived From Densely Substituted Unnatural Prolines As Precursors Of γ‑Peptides And Their Use In Organocatalysis

The synthesis of novel hybrid ferrocenylpyrrolidine ligands L_a^* and L_b^* via [3+2] cycloadditions has been described by our group.¹ Both ligands in turn provided densely substituted unnatural L- and D- proline derivatives in a stereodivergent manner. The powerful feature of having nitro and ester groups gives the opportunity to orthogonally synthesize different γ-proline oligopeptides with different substitution patterns and chiral centers. Supported by the efficiency of Proline‑based organocatalysts in numerous chemical transformations, our densely substituted pyrrolidine derivatives have been used in aldol reactions with good results.^1,2 In this communication, we present our results on the structure/activity relationship of the new generation of oligomeric catalysts. The main conclusion is that in the case of the g-dipeptides, the stereochemistry of the aldol adducts depends on both monomeric units in a nearly additive manner.