Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

摘要: Spirocyclic nitroxyl radicals (SNRs) are stable paramagnetics bearing spiro-junction at α-, β-, or γ-carbon atom of the nitroxide fragment, which is part heterocyclic system. Despite fact that first representatives SNRs were obtained about 50 years ago, methodology their synthesis and usage in chemistry biochemical applications have begun to develop rapidly only last two decades. Due presence spiro-function molecules, latter increased stability various reducing agents (including biogenic ones), while structures biradicals (SNBRs) comprises a rigid spiro-fused core fixes mutual position orientation moieties favors use dynamic nuclear polarization (DNP) experiments. This review on will give glance strategies for spiro-substituted, mono-, bis-nitroxides base six-membered (piperidine, 1,2,3,4-tetrahydroquinoline, 9,9′(10H,10H′)-spirobiacridine, piperazine, morpholine) five-membered (2,5-dihydro-1H-pyrrole, pyrrolidine, 2,5-dihydro-1H-imidazole, 4,5-dihydro-1H-imidazole, imidazolidine, oxazolidine) cores.