NMR study of products of thermal transformation of substituted N-aryl-o-quinoneimines

Products of thermal transformation of substituted N-aryl-o-quinoneimines were studied using NMR spectroscopy. The formation of 4aH-phenoxazine, which was further dimerized by the Diels—Alder reaction, was established.     

Kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of amines and polymethylbenzenes

A study of the kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of hydrogen donors (para-substituted N,N-dimethylanilines and polymethylbenzenes) showed that plots of the quantum yield of photoreduction (_H) and apparent reaction rate constant (k _H) vs. oxidation potential of hydrogen donors are extreme. In the presence of amines, k _H and _H increase, as a whole, whereas they decrease in the presence of polymethylbenzenes. In coordinates _H-G _e (G _e is the change in the free energy of electron transfer) for pairs quinone-H donor, _H increases with G _e approaching to zero. For the amine series, this effect is mainly in the exothermic region of G _e (G _e < 0). For the series of polymethylbenzenes, this increase is observed in the endothermic region (G _e > 0).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2381–2385, November, 2004.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Synthesis and structures of germanium-containing tungsten carbyne complexes Ph3gec≡w(ch2but)3 and Ph3GeC≡W(CH2SiMe3)3

New germanium-containing tungsten carbyne complexes Ph₃GeC≡W(CH₂R)₃ (R = Bu^t or SiMe₃) were synthesized by the reaction of the alkoxy derivative Ph₃GeC≡W(OBu^t)₃ with alkyllithium reagents RCH₂Li. The new compounds were isolated in individual form as crystals in 95 and 90% yields, respectively, and were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, and X-ray diffraction. X-ray diffraction study showed that the coordination environment of the W and Ge atoms in the Ph₃GeC≡ W(CH₂Bu^t)₃ and Ph₃GeC≡W(CH₂SiMe₃)₃ complexes can be described as a distorted tetrahedron. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 213—216, February, 2006.     

Photoreduction of o-benzoquinones in the presence of p-bromo-N,N-dimethylaniline

Photoreduction of o-benzoquinones in the presence of p-bromo-N,N-dimethylaniline under irradiation ( > 500 nm) affords the corresponding pyrocatechols and hydroxyphenyl ethers. The latter are unstable and, in turn, decompose in the dark reaction to pyrocatechols. The ratio between pyrocatechol and hydroxyphenyl ether formed upon the photoreaction is determined by the structure of o-quinone, namely, the presence and bulk of substituents in positions 3 and 6 of the ring. The yield of pyrocatechol is maximal (60—65%) if the substituents are the same (H and H, Bu^t and Bu^t) or insignificantly differ (Prⁱ and Bu^t), regardless of its bulk.     

Quinonimines and aminoquinones, the reaction products of 3,6-di(tert-butyl)-o-benzoquinone with primary and secondary amines

Reactions of 3,6-di(tert-butyl)-o-benzoquinone with primary amines occur by the nucleophilic 1,4-addition mechanism and lead to the corresponding 2-hydroxy-p-quinonimines, which exist in solutions in equilibrium with tautomeric 4-amino-o-quinones. The thermodynamic parameters of this prototropic isomerism were determined by NMR spectroscopy. In the case of a secondary amine (piperidine), a derivative of 4-amino-o-quinone was obtained; the corresponding o-semiquinone complexes were studied in solution by ESR spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1151–1155, July, 2006.     

New sterically hindered di-o-quinones of the biphenyl series

New di-o-quinones of the biphenyl series, namely, 2,2′-dialkyl-5,5′-di-tert-butylbiphenyl-3,4,3′,4′-diquinones, were synthesized. Their structures were established by IR and NMR spectroscopy. The molecular structure of 2,2′-dimethyl-5,5′-di-tert-butylbiphenyl-3,4,3′,4′-diquinone was established by X-ray structural analysis. The structure is characterized by orthogonal (the torsion angle is 82.9°) mutual arrangement ofo-benzoquinone fragments. ESR studies demonstrated that chemical reduction of diquinone proceeds in four oneelectron stages to form paramagnetic mono- and trianions as intermediates. Quinopyrocatechols, which are intermediates in the synthesis of di-o-quinones, were isolated and characterized. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 804–809, April, 1997.