When K' is reacted with 3b in the presence of Nmethyl maleimide (NMM), a different reaction trajectory unfolds and compound 4* is formed (Figure ). This conversion was witnessed by the methine signal of 3b shifting upfield and splitting into two multiplets at δ = 3.27 and 3.09 ppm (green). Further, the ring-opening of 3b caused an upfield shift of the β-methylene proton signal to δ = 2.73-2.53 ppm (yellow). Successful attachment of K' was reflected by the triplet signal of amidinium-adjacent protons at δ = 3.20 ppm (purple). The thiol-ene addition was characterized via the multiplet at δ = 4.04 ppm (orange), which represents the chiral maleimide proton close to the sulfur (Figure ). signments for 4* are found in the supporting information (Figure -37). Finally, unequivocal proof of product 4* was obtained through mass spectrometry, which shows the singly charged species (4*) + with a characteristic monoisotopic mass of m/z = 484.377 Da (Figure ). Conclusively, γ-substituted ITL derivative 3b is well capable to undergo chemo-and regio-selective modifi-cation depending on the present substrates. Similar to the thiolactones but with enhanced reactivity, a single or double modification strategy can be chosen offering fast and efficient reaction kinetics. In the single modification, the thiol that is released through ringopening of the ITL heterocycle cyclizes and thus gets re-protected to form a cyclic species. As opposed to thiolactones, this behavior can pose an advantage for systems where a permanently liberated thiol would cause adverse reactions.