Large-Scale Synthesis of Singh's Catalyst in a One-Pot Procedure Starting from Proline

A practical one-pot procedure for the preparation of Singh’s catalyst from either l-/d-proline or Boc-proline is described. The coupling partner, a chiral amino alcohol, can be prepared and used directly without purification from the corresponding amino acid ester. Moreover, a procedure for tert-butoxycarbonyl (Boc) group removal using concentrated HCl in MeOH–DCM was developed and utilized for the multigram-scale synthesis of Singh’s catalyst.