作者:John W. Mickelson、Kenneth L. Belonga、E. Jon Jacobsen
DOI:10.1021/jo00118a039
日期:1995.6
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 intramolecular 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.