(S)-4-(tert-Butoxycarbonyl)-2-phenylpiperazine is a chiral piperazine derivative featuring a phenyl substituent at the 2-position and a tert-butoxycarbonyl (Boc) protecting group on the nitrogen at the 4-position. This compound serves as a crucial chiral building block in medicinal chemistry. Its primary application is as a key intermediate in the synthesis of various pharmacologically active molecules. The chiral piperazine scaffold is a privileged structure found in numerous drug candidates targeting central nervous system (CNS) disorders, such as antipsychotics and antidepressants. The Boc group facilitates selective manipulation during multi-step synthetic sequences. As a versatile synthon, it is employed in the construction of complex molecules through reactions at the secondary amine or via further functionalization of the aromatic ring. It is commercially available from suppliers specializing in advanced pharmaceutical intermediates and chiral building blocks.