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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.
Berkessel et al. (Thu,) studied this question.
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