A novel method for the sterically shielded pyrrolidine nitroxides synthesis using donor–acceptor cyclopropanes

Taratayko, Andrey I.; Trakhinina, S. Yu.; Ломанович, К. А.; Kirilyuk, Igor A.

doi:10.1016/j.tetlet.2023.154546

Cited by 1 publication

(4 citation statements)

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“…Comparison of the EPR spectra of various sterically shielded nitroxides with a five-membered saturated ring (see, e.g., refs and ) shows that the value of a H may vary over a wide range, varying with minor structural changes. For example, in 1a – c , the increase of the substituent R by one methyl group leads to the growth of one of the two a H from 0.224 to 0.331 mT (R = i -Pr), but the addition of one more methyl group (R = t -Bu) results in the disappearance of one of the two a H .…”

Section: Results and Discussionmentioning

confidence: 99%

“…Recently, another pattern of the hyperfine structure was described for newly synthesized sterically shielded nitroxides 5 and 6 with only one large splitting of ca. 0.38–0.40 mT on a hydrogen atom. , …”

Section: Introductionmentioning

confidence: 99%

“…0.38−0.40 mT on a hydrogen atom. 11,15 Complicated hyperfine structure and line broadening in the EPR spectra of sterically shielded nitroxides makes them inefficient in EPRI and OMRI applications, where radicals with a minimal number of narrow lines are required for better resolution and enhancement. 16−18 Broadened spectral lines can also hamper analysis of molecular dynamics using spin labeling and EPR.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The original method we used for the preparation of various sterically shielded nitroxides, such as 1 , 2 , 5 , and 6 , implies the addition of ethynylmagnesium bromide to corresponding cyclic nitrone with the subsequent hydrogenation of the terminal acetylene group. ,, This method perfectly fits for the preparation of 3,4-bis(hydroxymethyl)-2,2,5,5-tetraethylpyrrolidine-1-oxyls with varying numbers and positions of deuterium atoms. A set of partly deuterated analogues of 1a were prepared.…”

Section: Introductionmentioning

confidence: 99%

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Origin of Long-Range Hyperfine Couplings in the EPR Spectra of 2,2,5,5-Tetraethylpyrrolidine-1-oxyls

Polienko,

Dobrynin,

Lomanovich

et al. 2023

ACS Omega

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Cyclic nitroxides with several bulky alkyl substituents adjacent to the nitroxide group are known to demonstrate a much higher stability to bioreduction than their tetramethyl analogues. Among these so-called “sterically shielded” nitroxides, the pyrrolidine derivatives are the most stable. The EPR spectra of some sterically shielded pyrrolidine-1-oxyls were reported to show one or two large additional doublet splittings with a hyperfine coupling (hfc) constant (ca. 0.2–0.4 mT). To determine the origin of these hfc, a series of 2-R-2,5,5-triethyl-3,4-bis(hydroxymethyl)-pyrrolidine-1-oxyls with methylene groups stereospecifically enriched with deuterium were prepared, and their CW EPR spectra were studied. In addition, these nitroxides were investigated using quantum chemical calculations on the UB3LYP/def2-TZVP level and NBO analysis. The apparent constants were assigned to hfc with γ-hydrogen in the side chain, with the contribution of the NBO orbital βπ*(N–O) to the natural localized molecular orbital βσ(C–H) playing the major role. This interaction is efficient if the ethyl substituent is in the pseudoaxial position of the ring and the CH2–CH3 bond is codirected with (parallel to) N–O. The apparent constant a H increases with the Boltzmann population of this conformation.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%