Enantioconvergent Synthesis of (−)-(2R,5S)-1-Allyl-2,5-dimethylpiperazine, an Intermediate to δ-Opioid Receptor Ligands

A convenient, high-yield enantioconvergent synthesis of (−)-1-allyl-(2S,5R)-dimethylpiperazine from trans-2,5-dimethylpiperazine has been developed. This compound is an important intermediate in the synthesis of δ-opioid receptor ligands. The process allows for the laboratory preparation of 100 g quantities of this enantiomerically pure diamine without chromatography. The key steps in the sequence were an efficient optical resolution using relatively inexpensive resolving agents, followed by interconversion of the unwanted (+)-enantiomer into the desired (−)-enantiomer.