Stereoselective Metal-Free Synthesis of β-Amino Thioesters with Tertiary and Quaternary Stereogenic Centers

beta-Amino thioesters are important natural building blocks for the synthesis of numerous bioactive molecules. An organocatalyzed Mannich reaction was developed which provides direct and highly stereoselective access to acyclic beta(2)- and beta(2,3,3)-amino thioesters with adjacent tertiary and quaternary stereocenters. Mechanistic studies showed that the stereochemical course of the reaction can be controlled by the choice of the substrates. The beta-amino thioesters were further functionalized by, for example, stereoselective decarboxylation to access beta(2,3)-frameworks. In addition, the value of the beta-amino thioesters was shown in coupling-reagent-free peptide synthesis.