– Lenalidomide 4′-alkyl-C3-azide (compound 4a), a chemically modified version of the orally active immunomodulator lenalidomide, is engineered for the synthesis of PROTACs. This compound, serving as a ligand for the ubiquitin E3 ligase cereblon (CRBN), integrates an Azide group, enabling it to participate in copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with alkyne-bearing molecules. Additionally, it can undergo strain-promoted alkyne-azide cycloaddition reactions (SPAAC) with molecules containing DBCO or BCN groups [1].