Synthesis of new homochiral 2,3-dialkylpiperazines derived from (R)-(-)-phenylglycinol

The synthesis of four new 2,3-dialkylpiperazines in yields of 70-99%, using (R)-(-)-phenylglycinol as a chiral inductor is described. The synthesis in volved reduction of the oxazino-oxazine type derivatives obtained by conden sation of glyoxal and phenylglycinol to give hydroxyethylenediamine precurs ors which were further condensed with glyoxal. butanedione and 1-phenyl-1,2 -propanedione and then reduced to provide the corresponding piperazines. Th e stereochemical outcome is determined by the configuration of the bisoxazo lidine precursors, which is in turn dictated by steric effects exerted by t he substituents on the five membered ring. The structures of five derivativ es were established by X-ray analysis. (C) 2001 Elsevier Science Ltd. All r ights reserved.