(3R,4S)-rel-3-Hydroxy-4-(2-propen-1-yl)-1-pyrrolidinecarboxylic acid 1,1-dimethylethyl ester is a chiral pyrrolidine derivative featuring a tert-butyloxycarbonyl (Boc) protecting group on the nitrogen atom, a hydroxyl group, and an allyl substituent. Its molecular formula is C12H21NO3. This compound is a key synthetic intermediate in the production of Boceprevir (SCH 503034), a potent and selective inhibitor of the hepatitis C virus (HCV) NS3 protease. Boceprevir was a significant antiviral drug used in the treatment of chronic hepatitis C genotype 1 infection. The specific stereochemistry (3R,4S) and the functional groups present in this intermediate are crucial for constructing the final active pharmaceutical ingredient (API) with the required biological activity. As a chiral building block, its synthesis and application are of primary importance in pharmaceutical process chemistry for the manufacture of this specific antiviral drug.