Asymmetric Synthesis of 2,6-Methylated Piperazines

Article abstract of DOI:10.1021/jo00118a039

The complete series of enantiopure 2,6-methylated piperazines was synthesized utilizing two alternative reactions in the key bond-forming step.The dimethyl enantiomers, (2R,6R)- and (2S,6S)-2,6-dimethylpiperazine (1, 2), were prepared using either a diastereoselective triflate alkylation or a novel intermolecular Mitsunobu reaction to set the required stereochemistry.The monomethyl derivatives, (R)- and (S)-tert-butyl 2-methyl-1-piperazinecarboxylate (3, 4) were also synthesized employing the Mitsunobu cyclization strategy while the trimethyl compounds, (R)- and (S)-2,2,6- trimethylpiperazine (5, 6) were prepared using an enantiospecific triflate alkylation as the principal reaction.These methods represent efficient, general strategies for preparing a variety of 2,6-methylated piperazines for which the absolute stereochemistry can be readily controlled.