Synthesis and Molecular and Crystalline Structure of Polyfluoro-1,3-Diazafluorenes

Reactions of 2-amino-3-(1-imino-2,2,2-trifluoroethyl)hexafluoro-1H-indene with carboxylic acid anhydrides and chlorides afforded 2-alkyl(aryl)-4-trifluoromethyl-5,6,7,8,9,9-hexafluoro-1,3-diazafluorenes. The molecular and crystalline structure of the products was studied by NMR spectroscopy and X-ray diffraction. 5,6,7,8,9,9-Hexafluoro-2-phenyl-4-trifluoromethyl-1,3-diazafluorene in crystal gives rise to infinite ladder chains via -stacking interaction between the benzene ring of one molecule and tetrafluorobenzene fragment of the other.     

Crystal structure of 2-nitropyridine

The crystal structure of 2-nitropyridine has been determined by x-ray diffraction analysis. The influence of the nitro group on the geometric parameters of the molecule was evaluated, as well as its influence on the molecular parameters of other nitropyridines, depending on the position of this group in the pyridine ring. Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090. E-mail: gatilov@nioch.nsc.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1367–1371, October, 1998.     

Investigation of conjugated dinitrones — derivatives of pyrroline oxide

The molecular structure of three derivatives ofbis(2- R- 5,5- dimethyl- 3- oxo- 1- oxide pyrrolin- 1- ylidene- 3),where R =CH ₃ (@#@5a @#@), C ₆H₅ (@#@5b @#@), C(CH ₃)₃ (@#@5c @#@), and of the complex of 5b with copper(II)hexafluoroacetylacetonate [Cu(hfac) ₂ (@#@5b @#@)] was investigated by X- ray diffraction analysis in the framework of our studies of the possible tautomeric equilibrium conjugated dinitrone ? nitroxide biradical. The pyrroline rings of the molecules under analysis are planar (rms deviations of atoms are no more than 0.041 å), and the interplanar angles are 32.01(5), 42.84(9), and 51.45(7)? for 5a,5b,and 5c,respectively. It is established that the bond lengths of the C(2)- C(3) =C(3a)- C(2a) fragment are equalized to C(2)- C(3) 1.42 and C(3)- C(3a) 1.40 å. The N→O bond lengths of the nitrone group are within 1.250(4)- 1.282(4) å) [in Cu(hfac)₂ (5b)]. The geometrical data obtained do not permit us to make an unambiguous choice between the tautomeric structures. The magnetic susceptibility measurements of the Cu(hfac)₂ solid complex (5b) and the absence of paramagnetism in solid compounds 5 indicate that they are diamagnetic.     

Photochemical synthesis of 1,2,3,4,5,6,8,9-octamethyl-C2V-bishomocubane

1,2,3,4,5,6,8,9-Octamethyl-C_2V-bishomocubane was prepared by the photochemical cyclization of 1R,3S,4,5,6R,8S,9,10-octamethyltricyclo[6.2.0.0^3,6]deca-4,9-di-ene in benzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1440–1442, June, 1991.The authors express their gratitude to V. I. Eroshkin for a number of valuable suggestions for carrying out the photochemical experiments.     

Crystal and molecular structure of 6b,7,8,8a-tetramethyl-6b,8a-dihydrocyclobut[a]acenaphthylene and 1,2,2a,10b-tetramethyl-2a,10b-dihydrocyclobuta[l]phenanthrene

The crystal and molecular structure of 6b,7,8,8a-tetramethyl-6b,8a-dihydrocyclobut[a]acenaphthylene (I) and 1,2,2a,10b-tetramethyl-2a,10b-dihydrocyclobuta[l]phenanthrene (II) is established by XRD analysis. The C(6b)-C(8a) bond in I is lengthened to 1.603(3) ∢, and the C(2a)-C(10b) bond in II is prolonged to 1.589(6) ∢. The acenaphthene and dihydrophenanthrene frameworks are planar; the rms deviations of atoms from the plane are 0.011 and 0.032 ∢, respectively. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1140–1145, November–December, 1997.     

Sesquiterpene Lactones from <Emphasis Type="Italic">Stizolophus balsamita</Emphasis> and Their Biological Activity

Four sesquiterpene lactones with the germacrane structure were isolated from the aerial part of Stizolophus balsamita. X-ray structure analyses showed that two of them were previously known balsamin derivatives. A third was a crystalline isomorphous mixture of the known lactone stizolin and 11,13-dihydrostizolin in a 53:47 ratio. The biological activities of the balsamin derivatives were investigated. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 454–457, September–October, 2005.     

Effects of Spiro-Cyclohexane Substitution of Nitroxyl Biradicals on Dynamic Nuclear Polarization

Spiro-substituted nitroxyl biradicals are widely used as reagents for dynamic nuclear polarization (DNP), which is especially important for biopolymer research. The main criterion for their applicability as polarizing agents is the value of the spin–spin exchange interaction parameter (J), which can vary considerably when different couplers are employed that link the radical moieties. This paper describes a study on biradicals, with a ferrocene-1,1′-diyl-substituted 1,3-diazetidine-2,4-diimine coupler, that have never been used before as DNP agents. We observed a substantial difference in the temperature dependence between Electron Paramagnetic Resonance (EPR) spectra of biradicals carrying either methyl or spirocyclohexane substituents and explain the difference using Density Functional Theory (DFT) calculation results. It was shown that the replacement of methyl groups by spirocycles near the N-O group leads to an increase in the contribution of conformers having J ≈ 0. The DNP gain observed for the biradicals with methyl substituents is three times higher than that for the spiro-substituted nitroxyl biradicals and is inversely proportional to the contribution of biradicals manifesting the negligible exchange interaction. The effects of nucleophiles and substituents in the nitroxide biradicals on the ring-opening reaction of 1,3-diazetidine and the influence of the ring opening on the exchange interaction were also investigated. It was found that in contrast to the methyl-substituted nitroxide biradical (where we observed the ring-opening reaction upon the addition of amines), the ring opening does not occur in the spiro-substituted biradical owing to a steric barrier created by the bulky cyclohexyl substituents.     

Synthesis and Antibacterial Activity of Caffeine Derivatives Containing Amino-Acid Fragments

Chemistry of Natural Compounds - Cross-coupling of 8-bromocaffeine, 8-bromo-1-butyltheobromine, or 8-bromo-7-butyltheophylline with α-, β-, or ω-amino-acid methyl or t-butyl ester...     

Synthesis of a new class of bisheterocycles via the Heck reaction of eudesmane type methylene lactones with 8-bromoxanthines

The eudesmane-type methylene lactones (isoalantolactone, alantolactone, 4,15-epoxyisoalantolactone, 2′,2′-dichloro-4H-spiro[cyclopropane-1′,4-eudesma-11(13)-en-8β,12-olide], and alantolactone) react with 8-bromoxanthines (8-bromocaffeine, 8-bromotheobromine, 8-bromo-3-butyltheobromine, 8-bromotheophylline, 8-bromo-9-butyltheophylline) under Heck reaction conditions to produce the target (E)-13-(2,6-dioxo-2,3-dihydro-1H-purin-8-yl)eudesma-4(15),11(13)-dien-8β,12-olides and the subsequent endocyclic isomers - 11-(2,6-dioxo-2,3-dihydro-1H-purin-8-yl)-13-normethyleudecma-4(15)-7(11)-dien-8α,12-olides. It was revealed that the yield and product ratio depends on the reaction conditions and the structure of methylene lactone. The effectiveness of Pd(OAc)₂–caffeine catalytic system has been demonstrated in this reaction. The electric eel acetylcholinesterase inhibitory activity of the eudecmanolide-xanthine hybrids was evaluated. Among the new type bisheterocycles compound 27 with butyl and 2-oxodecahydronaphtho[2,3-b]furan-3(2H)-ylidene)methyl substituents at C-7 and C-8 of the xanthine core showed moderate activity with IC₅₀ value of 40 μM.     

X-ray diffraction investigation of perfluoro-4-methylenecyclohexa-2,5-dienones

Perfluorinated 8-phenyl-7,8-diethylbicyclo[4.2.0]octa-1,4,6-trien-3-one (3), 2-(4-oxocyclohexa-2,5-dienylidene)-1,1-diethylbenzocyclobutene (4) and 2-(4-oxocyclohexa-2,5-dienylidene)-5-(2-phenyl-cis-1,2-diethylbenzocyclobuten-1-yloxy)-1,1-diethylbenzocyclobutene (5), including the 4-methylencyclohexa-2,5-dienone fragment, were prepared by the reaction of perfluoro-1,1-(1) and-1,2-diethylbenzocyclobutene (2) with pentafluorobenzene in SbF₅. Single crystal X-ray diffraction study of compounds 3–5 revealed that the oxygen atom of the C=O group participated in the formation of supramolecular architectures in all three compounds, and C=O…π bonding may be considered as the corresponding synthon (with increased separation in the case of compound 5). C-F…π bonding acts as a second synthon. F…F interactions in crystals 3–5 were classified as stabilizing or enforced.