Azethoxyl Nitroxide Spin-Labeled Crown Ethers and Cryptands with the N-O. Group Positioned near the Cavity

Article abstract of DOI:10.1021/jo00164a004

We report the synthesis and complexation properties of several nitroxide spin-labeled crown ethers and cryptands in which the N-O. group, in certain conformations, is thrust toward the cavity of the molecule.While initial approaches involving the cyclization of various unsymmetrically substituted tetraethylene glycols (e.g, 10, 11, and 15) were not promising, success was achieved by the sequential addition of substituted phenyl groups to nitrone 28, leading to nitroxide crown ethers 37 and 38.Nitroxide cryptand 60 was prepared by diacylation of diaza-18-crown-6 51 with azethoxyl nitroxide diacid chloride 57 followed by reduction.The ESR spectrum a_N values of these nitroxides were not sensitive to the presence of K⁺, Na⁺, or Li⁺ in MeOH, While diaza-18-crown-6, decamethylene cryptand 55, and nitroxide cryptand 60 formed 1:1 complexes with NaBPh₄ in CDCl₃, nitroxide crown ethers 37 and 38 and amide 54 did not.Adaption of the quantitative methodology of Cram et al. showed that 55 and 60 bind Na⁺ somewhat better than dicyclohexyl-18-crown-6.K⁺ is bound better than Na⁺ by 55 and 60, tough not as strongly as dicyclohexyl-18-crown-6.The binding of K⁺ and Na⁺ by 37 and 38 is minimal.