A new method for the reduction of nitronyl nitroxides

Reduction of nitronyl nitroxides using hexamethylenetetramine is a very convenient method for preparing the corresponding imino nitroxides and 2-imidazoline N-oxides.     

ω-hydro-perfluoroalkyl pyrimidinyl nitroxides

Twenty-two polysubstituted 2-aminopyrimidines dissolved in F1 13 (CC1F₂-CCl₂F) solutions containing ([H(CF₂CF₂)_nCO₂]₂ n = 1,2) and H(CF₂CF₂)_nNO [? H(CF₂CF₂)_n ^? + NO] have been oxidized into detectable ω-H-perfluoroalkyl pyrimidinyl nitroxides along with neutral products. A mechanism involving Habstraction from the amino groups by H(CF₂CF₂)_nN(O^?)(CF₂CF₂)_nH and the subsequent radical steps was suggested for the generation of the nitroxides. Some relationships between a_N values and the nature of the ring substituents are discussed.     

Pyrimidinyl nitronyl nitroxides

The chemistry of 2,2,4,4-substituted pentane derivatives has been investigated with the aim of providing a flexible and versatile synthetic route to pyrimidinyl nitronyl nitroxides, in which the bis-N-oxy fragment is incorporated in a six-membered ring. The synthesis of 2,4-diamino-2,4-dimethylpentane and 2,4-bis(hydroxylamino)-2,4-dimethylpentane, convenient precursors of these nitroxides, is described and full characterization of a series of pyrimidinyl nitronyl nitroxides is reported, along with a preliminary study of their coordination properties.     

Synthesis of dipolar nitronyl nitroxides

The synthesis of a nitronyl nitroxide radical with a dipolar (mesomeric betaine) unit is reported.     

1,3-Dipolar cycloaddition in the synthesis of pyrazolyl-substituted nitronyl nitroxides

A new approach to the synthesis of polyfunctional pyrazolyl-substituted nitronyl nitroxides was developed based on the presynthesized pyrazole derivatives prepared by 1,3-dipolar cycloaddition. The structures of the resulting mono-and biradicals were confirmed by X-ray diffraction. Dedicated to Academician A. L. Buchachenko on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2105–2116, September, 2005.     

A novel TTF-based donor carrying four nitronyl nitroxides

A novel TTF-based tetraradical donor was synthesized and its electronic structure was fully characterized by spectroscopic measurements, magnetic susceptibility measurements, and electrochemical analyses.     

Electrochemistry of nitronyl and imino nitroxides

Redox potentials of a wide group of azolyl-substituted nitronyl and imino nitroxides were determined by classic cyclic voltammetry (CV). Conclusions have been made for this group of compounds, and their peculiarities were emphasized in comparison with methyl-, phenyl-, iodo-, and cyano-substituted nitroxides.     

A versatile synthesis of a new bisiminophosphorane

The iminophosphorane CH₂CH₂[P{NP(O)(OPh)₂}Ph₂]₂ is synthesized in high yields (80–97%) via a very convenient procedure using diphenylphosphoryl azide (DPPA) and 1,2-bis(diphenylphosphino)ethane.     

Synthesis and redox properties of imidazol-2-yl-substituted nitronyl nitroxides

Russian Chemical Bulletin - New nitronyl nitroxide radicals, 2-(4′(5′)-methylimidazol-2′-yl)- and...     

Preparation and characterization of new chiral nitronyl nitroxides bearing a stereogenic center in the imidazolyl framework

A synthetic procedure for optically active and racemic alpha-nitronyl nitroxides (alpha-NNs) having a stereogenic center at the 4-position of the imidazolyl ring is described. This procedure consists of (1) the synthesis of a dissymmetric vic-dinitro compound by Kornblum reaction, (2) the enantiomeric resolution of the racemate by a diastereomer method for obtaining the optically active sample, (3) the quick reduction of the optically active or racemic vic-dinitro compound to the bis(hydroxyamino) derivative with Al/Hg, (4) the solvent-free condensation of the bis(hydroxyamino) compound with an aldehyde to give the 1,3-dihydroxyimidazolidine, and (5) the final oxidation of the alpha-NN precursor with aqueous NaIO(4). The absolute configuration of the optically active alpha-NNs was assigned by correlating with the X-ray crystal structure of the (-)-(1S,4R)-camphanic acid ester derivative of the optically active vic-dinitro compound. The molecular conformation of the optically active alpha-NNs was found to be folded both in solution and in the solid state by CD spectroscopy and energy minimization with the Monte Carlo method. The magnetic properties of both optically active and racemic alpha-NNs in solution and in the solid state were characterized by EPR spectroscopy and magnetic susceptibility measurement, respectively.     

Controlled radical polymerization of styrene in the presence of nitronyl nitroxides

Bulk radical polymerization of styrene in the presence of nitronyl nitroxides (2-(4-substituted phenyl)-4,4,5,5-tetramethyl-4,5-dihydroimidazolyl-1-oxyl 3-oxide) was studied. All nitronyl nitroxides, like other nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO), act as reversible radical scavengers. The efficiency of controlling the polymerization is affected by the substituent at the 4′-position. The efficiency increases with electron donating strength of 4′-substituents, at least at the beginning of the reaction. However, the thermal stability of nitronyl nitroxides decreases in the same order. Thus, TEMPO is more suitable than nitronyl nitroxides for controlled/“living” radical polymerization of styrene.     

Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides

It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (HL¹) and pyrazol-3-yl-substituted imino nitroxide (HL³) with Cu(II) acetate lead to self-assembly of the Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ tetranuclear and Cu₂(OAc)₂(H₂O)₂(L³)₂ dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (HL²) gave unexpected solid Cu₂(H₂O)₂(L⁶)₂ · 2DMF, in which L⁶ is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting HL². A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (HL⁴). It led to the formation of Cu₂(DMF)₂(L⁷)₂, where L⁷ is deprotonated 2-(5-carboxy-1H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(OAc)₂(H₂O)₂(L³)₂, the L¹ and L³ paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu₂(H₂O)₂(L⁶)₂ · 2DMF and Cu₂(DMF)₂(L⁷)₂, the paramagnetic L⁶ and diamagnetic L⁷ are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(H₂O)₂(L⁶)₂ · 2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu₂(OAc)₂(H₂O)₂(L³)₂ reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II) ← N=C–N ? O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids.     

A new versatile synthesis of 4-substituted diaminopyridine derivatives

A new convenient method for the synthesis of substituted 2,6-diacetamido pyridines has been developed. It starts from 4-hydroxypyridine and comprises the introduction of the amino groups by the Chichibabin reaction. After several protection and deprotection steps 2,6-diacetamido-4-hydroxy pyridine is obtained, which is regarded as a key compound for the synthesis of various substituted 2,6-diacetamido pyridines. It is shown that the free hydroxy group is susceptible for nucleophilic substitution. This provides an easy access to the introduction of different functional groups at 4-position of 2,6-diacetamido pyridine. The advantages over other procedures described in the literature are discussed.     

A new efficient and versatile synthesis of alkyl prosphorylcholines

A short and general synthetic method is described for the preparation of new phosphorylcholines.     

A versatile new strategy for the synthesis of tropolones

Swern-type oxidation of various 7-halogenobicyclo[4.1.0]heptane-2,3- or -3,4-diols affords the corresponding bicyclic diketones which undergo ^{in situ} ring expansion and loss of hydrogen halide to give α-tropolones in high yield. The quantitative conversion of the isolable 1,4-diketone 26 into the γ-tropolone acetate 27 has been achieved.     

Syntheses and structures of azol-1-yl derivatives of nitronyl and imino nitroxides

2-(Pyrazol-1-yl)-, 2-(imidazol-1-yl)-, 2-([1,2,4]triazol-1-yl)-, and 2-(benzotriazol-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl were prepared by reactions of 2-bromo-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (NIT-Br) with the corresponding sodium azolides. In prepared 2-(azol-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, the NIT-N_Het bond is readily hydrolyzed. Reduction of imidazole-3-oxide-1-oxyls leads to corresponding 2-(azol-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyls, which are much more stable against hydrolysis. The structures of spin-labeled imidazoles, [1,2,4]triazoles and benzotriazoles are confirmed by X-ray analysis, showing that the paramagnetic molecules form packings with motifs from centrosymmetric dimers to topologically linear chains.     

Photochromism of diarylethenes with two nitronyl nitroxides: photoswitching of an intramolecular magnetic interaction

Photochromic diarylethenes that have p-phenylene-substituted benzothiophene aryl groups with and without nitronyl nitroxide radicals at both ends of the molecules were synthesized. The absorption maxima of the closed-ring isomers showed a hypsochromic shift with the increase in the pi-conjugated chain length. The unique behavior was attributed to the stabilization by the resonant quinoid structures. Both photocyclization and photocycloreversion quantum yields of the diarylethene with nitronyl nitroxide radicals were found to increase with the increase in the pi-conjugated chain length. Photoswitching of the magnetic interaction between two nitronyl nitroxide radicals was studied by means of ESR spectroscopy. The change in exchange interaction between open- and closed-ring isomers of 1,2-bis[6-[4-[4-(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolin-2-yl)phenyl]phenyl]-2-methyl-1-benzothiophen-3-yl]hexafluorocyclopentene was determined to be more than 30-fold.