(2S,4R)-4-Ethyl-2-hydroxymethyl-1-pyrrolidinecarboxylic Acid tert-Butyl Ester is a chiral pyrrolidine derivative widely utilized as a key intermediate in organic synthesis and pharmaceutical applications. Its stereochemically defined structure, featuring both hydroxymethyl and ethyl substituents, makes it valuable for constructing complex molecules with high enantiomeric purity. The tert-butyl ester group enhances stability and facilitates further functionalization under mild conditions. This compound is particularly useful in asymmetric synthesis, serving as a precursor for biologically active compounds, including protease inhibitors and other therapeutic agents. Its well-defined configuration ensures reproducibility in synthetic routes, while its modular reactivity allows for versatile modifications, making it a preferred choice for medicinal chemistry and fine chemical production.