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 involved reduction of the oxazino-oxazine type derivatives obtained by condensation of glyoxal and phenylglycinol to give hydroxyethylenediamine precursors which were further condensed with glyoxal, butanedione and 1-phenyl-1,2-propanedione and then reduced to provide the corresponding piperazines. The stereochemical outcome is determined by the configuration of the bisoxazolidine precursors, which is in turn dictated by steric effects exerted by the substituents on the five membered ring. The structures of five derivatives were established by X-ray analysis.