A process for a stereoselective preparation of novel chiral nitrogen mustard derivatives useful in synthesizing optically active 1,4-disubstituted piperazines of formula: ##STR00001## wherein R, Ar, and Q are defined as set forth herein, and intermediate compounds therefor. The 1,4-disubstituted piperazines act as 5HT1A receptor binding agents useful in the treatment of Central Nervous System (CNS) disorders. The intermediate compounds of Formula II and IV as set forth herein are also included.