2,4,5-Trichlorophenol

Experimental procedure: A mixture of DCC (1 mmol) and 2,4,5-trichlorophenol (1 mmol) in DMF (50 mL) is cooled to －10 °C and treated dropwise with a solution of cyclopentane carboxylic acid (1 mmol) in DMF (10 mL). The reaction mixture is allowed to warm to room temperature and is stirred overnight. Removal of the solvent under reduced pressure affords a white solid. The solid is triturated with ethyl acetate (50 mL), and the dicyclohexylurea is removed by filtration. Filtrate is evaporated under reduced pressure to afford oil. Flash chromatography on silica gel using EtOAc/hexanes (1:9) gives an active ester (1) in 88% yield.
A solution of 1 (1 mmol) in EtOAc (10 mL) is added dropwise to substituted L-histidine methyl ester (1 mmol) in EtOAc (50 mL) during 15 min, and the reaction mixture is stirred at ambient temperature for 24 h. Complete removal of the solvent in vacuo gives crude product. Flash column chromatography on silica gel using a solvent system of EtOAc/CH₃OH (94:6) provides 2 (yield is not shown).