Synthesis of bis-α-amino acids through proline catalyzed asymmetric α-amination of higher homologs of Garner's aldehyde

A very convenient synthesis of bis-α-amino acids from the higher homologs of Garner's aldehyde is reported. The key step is proline catalyzed asymmetric amination of the aldehydes using dibenzylazodicarboxylate. The aldehydes used are either commercially available or can easily be prepared from aspartic or glutamic acid. One of the two chiral centers in the bis-amino acids comes from the aldehyde and the other one is generated through the proline catalyzed reaction, which were high yielding and proceeded with very high diastereoselectivity (93–99%). The reported route offers a general method for the synthesis of the title compounds with desired stereochemical outcome.