Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• -system. According to EPR data, the authors suggested that iminoxyl radicals 101 generated from oximes 100 by photolysis with the addition of the di-tert-butyl peroxide gave nitroxides 102 [123]. The widespread use of iminoxyl radicals in organic synthesis involving a radical addition to a C=C bond

Unexpected one-pot formation of the 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and EPR study

• Sergey A. Dobrynin,
• Igor A. Kirilyuk,
• Yuri V. Gatilov,
• Andrey A. Kuzhelev,
• Olesya A. Krumkacheva,
• Matvey V. Fedin,
• Michael K. Bowman and
• Elena G. Bagryanskaya

Beilstein J. Org. Chem. 2019, 15, 2664–2670, doi:10.3762/bjoc.15.259

• a sterically shielded polycyclic nitroxide. The EPR spectra and spin relaxation behavior of the nitroxide were studied in solution. The spin relaxation seems well suited for the use as a biological spin label and are comparable with those of cyclic nitroxides with two spirocyclic moieties adjacent

• cyclopentanone and ammonia. The polycyclic amine product was then converted into a sterically shielded polycyclic nitroxide. Sterically hindered nitroxides have high chemical stability [5] and can be used as spin labels to study biopolymers in cells [6]. The introduction of spirocyclic moieties has a smaller

• effect on the reduction rates of nitroxides than does the introduction of linear alkyl substituents. However, spirocyclic nitroxides may have much longer spin relaxation times at 70–150 K which make them attractive agents for spin labeling [7][8][9]. Sterically hindered nitroxides can be used as spin

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• 630090, Russian Federation Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, Institutskaya 3, Novosibirsk 630090, Russian Federation 10.3762/bjoc.15.200 Abstract Sterically shielded nitroxides of the pyrrolidine series have shown the highest resistance to reduction. Here we report the

• synthesis of new pyrrolidine nitroxides from 5,5-dialkyl-1-pyrroline N-oxides via the introduction of a pent-4-enyl group to the nitrone carbon followed by an intramolecular 1,3-dipolar cycloaddition reaction and isoxazolidine ring opening. The kinetics of reduction of the new nitroxides with ascorbate were

• studied and compared to those of previously published (1S,2R,3′S,4′S,5′S,2″R)-dispiro[(2-hydroxymethyl)cyclopentan-1,2′-(3′,4′-di-tert-butoxy)pyrrolidine-5′,1″-(2″-hydroxymethyl)cyclopentane]-1′-oxyl (1). Keywords: aldonitrone; 1,3-dipolar cycloaddition; pyrrolidine nitroxides; 1-pyrroline-N-oxide

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• , Japan Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan 10.3762/bjoc.15.84 Abstract Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive

• counterparts (65.8% vs 85.5%). Keywords: caged compound; nitroxide; photolysis; radical; theranostics; two-photon; Introduction Nitroxides (aminoxyl radicals) possess a delocalized unpaired electron and exhibit negligible dimerization reactivity, making them persistent open-shell species [1][2][3][4]. In

• addition to their ease of handling, nitroxides are highly sensitive to electron paramagnetic resonance (EPR) spectroscopy and redox reactions. Therefore, nitroxides have been developed and utilized in diverse and crucial applications, not only in chemistry, but also in biology, physiology, and energy

Phosphoramidite building blocks with protected nitroxides for the synthesis of spin-labeled DNA and RNA

• Timo Weinrich,
• Eva A. Jaumann,
• Ute M. Scheffer,
• Thomas F. Prisner and
• Michael W. Göbel

Beilstein J. Org. Chem. 2018, 14, 1563–1569, doi:10.3762/bjoc.14.133

• measure long distances that are hardly accessible by NMR [9][10]. Furthermore, spin labeling of biopolymers can support NMR studies by paramagnetic relaxation enhancement [11][12]. For nucleic acids, spin labeling is most often achieved by covalent attachment of nitroxides. Unfortunately, the conditions

• required to assemble oligonucleotides by phosphoramidite chemistry and to ligate them enzymatically, are known to partially degrade nitroxides. This problem can be reduced by postsynthetic introduction of the spin label [13][14][15][16][17][18][19][20][21][22][23][24]. Starting from convertible nucleotides

• , for example, nucleophilic displacement by 4-amino-TEMPO has been used to prepare RNA strands containing the cytidine derivative 1 and its adenosine analog 3 [8][25][26] (Figure 1). Alternatively, by adapting the standard synthetic procedures, nitroxides can be directly incorporated into

Reactions of nitroxides 15. Cinnamates bearing a nitroxyl moiety synthesized using a Mizoroki–Heck cross-coupling reaction

• Jerzy Zakrzewski and
• Bogumiła Huras

Beilstein J. Org. Chem. 2015, 11, 1155–1162, doi:10.3762/bjoc.11.130

• -oxyl; cinnamates; Mizoroki–Heck cross-coupling reaction; nitroxides; Introduction Cinnamic acid derivatives are known as biologically active compounds. Cinnamic acid and its hydroxy derivatives bearing a phenolic moiety such as coumaric, caffeic, ferulic, sinapinic, and chlorogenic acids [2][3][4][5

• moiety), recently applied in the Morita–Baylis–Hillmann reaction [21]. The use of nitroxides in cross-coupling reactions is described only in a limited number of papers [22][23][24][25][26][27][28][29][30][31][32]. To the best of our knowledge, there are no systematic studies on the use of nitroxides in

• the Mizoroki–Heck cross-coupling reaction. Despite the observation that an unpaired electron in nitroxides does not participate in organic reactions has been well known since the beginning of the nitroxide progress in 60's [33] the reactions of nitroxides involving an unpaired electron are also

Practical synthesis of aryl-2-methyl-3-butyn-2-ols from aryl bromides via conventional and decarboxylative copper-free Sonogashira coupling reactions

• Andrea Caporale,
• Stefano Tartaggia,
• Andrea Castellin and
• Ottorino De Lucchi

Beilstein J. Org. Chem. 2014, 10, 384–393, doi:10.3762/bjoc.10.36

• able to couple aryl bromides with terminal alkynes, including a couple of examples with 2-methyl-3-butyn-2-ol, in moderate yield [35]. Two simple reaction protocols for the copper-free coupling of 4 have been also reported for iodo nitroxides [30] and cyclopropyl iodides [29]. Herein, we present two

Stability of SG1 nitroxide towards unprotected sugar and lithium salts: a preamble to cellulose modification by nitroxide-mediated graft polymerization

• Guillaume Moreira,
• Laurence Charles,
• Mohamed Major,
• Florence Vacandio,
• Yohann Guillaneuf,
• Catherine Lefay and
• Didier Gigmes

Beilstein J. Org. Chem. 2013, 9, 1589–1600, doi:10.3762/bjoc.9.181

• solubilize cellulose in N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA) with 5 to 10 wt % of lithium salts (LiCl or LiBr), and carry out grafted polymerization in this medium. The stability of nitroxides such as SG1 has not been studied under these conditions yet, even though these parameters are

• activation–deactivation equilibrium, all the chains grow at the same rate affording a living/controlled polymerization. Several nitroxides have been synthesized since their first development in the 1980s [11]. In particular, the cyclic nitroxide TEMPO has been intensely studied [21][22] in the polymerization

• of styrene derivatives. Another important property of TEMPO is that it is reduced by reducing sugars such as glucose [18]. The consumption of nitroxides by reducing agents such as a sugar or a polysaccharide is of prime importance when aiming at the synthesis of glycopolymers or the graft

Reactions of nitroxides XIII: Synthesis of the Morita–Baylis–Hillman adducts bearing a nitroxyl moiety using 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a starting compound, and DABCO and quinuclidine as catalysts

• Jerzy Zakrzewski

Beilstein J. Org. Chem. 2012, 8, 1515–1522, doi:10.3762/bjoc.8.171

• aldehydes. Keywords: 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl; DABCO; Morita–Baylis–Hillman reaction; nitroxides; quinuclidine; Introduction In the Morita–Baylis–Hillman (MBH) reaction, aldehydes react with a double bond activated by an electron-withdrawing group (EWG). The vinylic carbon

• of biological importance [35][36][37][38][39][40][41][42][43]. The MBH reaction is a rather slow process (complete reaction can take hundreds of hours), especially when acrylates are used [44]. As has been very well known since the 1960s, stable nitroxides can react without affecting the unpaired

• : 124.12520; found: 124.12515; for m/z 109: calcd for C8H13: 109.10173; found: 109.10079. However, direct characterization of the adducts 5a–o by NMR is impossible, one of the adducts (5d, R = C6H5) was subjected to the exemplary experiment developed for nitroxides by Keana and coworkers in 1975 [54]. 5d was