Lenalidomide 4′-alkyl-C3-azide (compound 4a) is a click chemical modified Lenalidomide (HY-A0003) that can be used to synthesize PROTACs. Lenalidomide is an orally active immunomodulator and a ligand for the ubiquitin E3 ligase cereblon (CRBN). Lenalidomide 4′-alkyl-C3-azide contains an Azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. Strain-promoted alkyne-azide cycloaddition reactions (SPAAC) can also occur with molecules containing DBCO or BCN groups^[1].