Highly diastereoselective preparation of anti-α,β-dialkyl β-amino acids containing natural α-amino acid side chains

An asymmetric synthesis of anti-2,3-diamino acids is reported. The enolates of N,N-dibenzylated b3-amino esters were treated with di-tert-butyl azodicarboxylate (DBAD) to afford their N0,N00-di-Boc-2-hydrazino derivatives with excellent anti diastereoisomeric ratio. Final Boc removal and reductive cleavage of the hydrazino bond led to the expected 2,3-diamino esters having only one free amino group. In comparison with other asymmetric C-2 amination procedures, this method does not need the use of expensive chiral reagents and/or chiral auxiliaries, while leads to products which can be orthogonally protected.