Different aspects had to be considered to design the synthesis of the target molecule. In particular, the TEMPO group was introduced at the latest possible stage of the synthetic pathway. This approach allows us to i) develop a generalized synthesis method for preparing diazoniums with various functional groups, ii) limit the synthesis cost by adding the most expensive synthon at the final stage of the reaction sequence, and iii) preserve the integrity of the TEMPO moiety, which is sensitive to acidic conditions. For the latter reason, the group chosen to protect the amine function of 4aminobenzoic acid was the 9-fluorenylmethoxycarbonyl (Fmoc) group , which can be removed under mildly basic conditions (by proton abstraction with secondary amines such as piperidine). Compound dC12TEMPO was synthesized according to the procedure shown in Scheme 1 (see details in SI-2). Fmoc-protected 4-aminobenzoic acid (compound 1) and benzyl ester of 2-aminododecanoic acid (compound 2) were obtained as previously reported. These two protected compounds were coupled using dicyclohexylcarbodiimide (DCC) and N-hydroxybenzotriazole (HOBt) as activating agents, giving amide 3 in good yield (80%). The benzylic ester group of compound 3 was then removed using an HBr solution in acetic acid, without affecting the Fmoc protecting group. The resulting acid, compound 4, was reacted with 4-aminoTEMPO using the same activating agents as previously, yielding compound 5 in 75%. Finally, removing the Fmoc group of compound 5× using piperidine led to the formation of the aniline compound 6, a precursor of the target diazonium salt. To synthesize the diazonium cation dC12TEMPO from compound 6, two diazotization methods described in the literature were explored in organic media. The first method involved the use of nitrosonium tetrafluoroborate (NOBF4) , which served both as a nitrosating agent and a source of BF4 -. The second method utilized tert-butyl nitrite (tBuONO) as the nitrosating agent in combination with the boron trifluoride complex (BF3-CH3CN) as the counter-ion source for BF4 -. Given that nitrosating agents (NOBF4 and tBuONO) possess oxidizing properties and that the BF3-CH3CN complex can act as a Lewis-acid , the TEMPO group attached to target molecules might experience changes in its redox state during diazotization, potentially undergoing oxidation or disproportionation. In each case, an excess of reagents was employed to guarantee an adequate supply for diazotization (2.4 eq. NOBF4 or 1.2 eq. tBuONO + 4.0 eq. BF3-CH3CN), accounting for side reactions involving the TEMPO group.