In previous work we demonstrated that implementing additional substituents in piperidinyl nitroxides can induce spirocyclic scaffolds to adopt more sterically shielded closed conformations. This leads to enhanced stability towards reduction, while simultaneously maintaining the excellent relaxation properties of spirocyclic nitroxide scaffolds. However, as the 5-membered pyrrolinyl and pyrrolidinyl nitroxides are inherently even more stable, we hypothesized that suitably substituted derivatives of these scaffolds could possess even higher stabilites. In this study, we report the development of a novel family of spirocyclic pyrrolidinyl nitroxides with an exocyclic methylene substituent (Figure ). The conformations adopted by nitroxides based on this scaffold were investigated by single crystal X-ray diffraction (SC-XRD), and stability to reduction was assessed by continuous wave (CW) EPR spectroscopy and cyclic voltammetry (CV). The electron spin relaxation parameters Tm and T1 of the new scaffold were also measured by pulsed EPR methods across a range of temperatures. Our findings indicate that the new spirocyclic exo-methylene nitroxides are promising scaffolds for the development of reduction resistant spin labels for elevated-temperature DEER measurements or DNP polarising agents.