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991.
Two oxidation reactions are described which result in the selective degradation of the furan ring in khellin. Conversion of these products to previously inaccessible analogues is described. 相似文献
992.
Ronald J. Pugmire James C. Smith David M. Grant Branko Stanovnik Miha Tiler Bojan Ver
ek 《Journal of heterocyclic chemistry》1987,24(3):805-809
Carbon–13 nuclear magnetic resonance data have been acquired on 22 azoloazines. Chemical shifts have been correlated by a step–wise linear multiple regression with nitrogen substituents in both the 5- and 6-membered rings using pyrrolo[1,2-α]pyridine as the reference for chemical shift correlation. The data demonstrate that a highly correlated set of chemical shift parameters exist. Nitrogen substitution in the five–membered ring produces larger cross–ring effects than are oberved in the five–membered ring when substitution occurs in the six–membered ring. Within the six–membered ring a constant para- substituent parameter is noted. The meta- and para- parameters are more complex and fall into two groups for each parameter. Within the five–membered ring, a highly regular chemical shift pattern is observed which reflects an attenuated perturbation from nitrogen substitution in the six–membered ring. 相似文献
993.
Robert N. Haszeldine Ronald Rowland Robin P. Sheppard Anthony E. Tipping 《Journal of fluorine chemistry》1985,28(3):291-302
Reaction of hexafluoropropene (HFP) with a series of alcohols under thermal, photochemical or peroxide-initiated conditions affords the 1:1 adducts CF3CHFCF2CR1R2OH (R1 = H, R2 = H, Me, Prn or CF3; R1 = Me, R2 = Me or Et) in high yield via a radical chain mechanism. Adduct are not formed with the alcohols (CF3)2CHOH and CF3CHFCF2CH2OH. Other 1:1 adducts of structure CHF2CF(CF3)CH2OH and CH3(C2H3CF2CHFCF3)CH2OH are formed as minor products in the methanol and -butanol reactions, respectively. 相似文献
994.
995.
Ronald W. Johnson Ronald J. Matlson J. Walter Sowell 《Journal of heterocyclic chemistry》1977,14(3):383-385
A facile route for the synthesis of substituted 2-amino-3-cyano-4-methylpyrroles from N-acetyl-α-amino ketones and malononitrile is reported. 相似文献
996.
Efficient new syntheses of the o-quinone derivatives of benzo[a]pyrene (BPQ), 7,12-dimethylbenz[a]anthracene (DMBAQ), and benz[a]anthracene (BAQ), implicated as active carcinogenic metabolites of the parent polycyclic aromatic hydrocarbons (PAHs), are reported. These PAH quinones also serve as starting compounds for the synthesis of the other active metabolites of these PAHs thought to be involved in their mechanism(s) of carcinogenesis. The latter include the corresponding o-catechols, trans-dihydrodiols, and the corresponding anti- and syn-diol epoxides. 相似文献
997.
The distribution of center of mass electrophoretic mobility mobilities and normalized migration time of up to 1080 lambda DNA molecules per experiment were measured in both semidilute hydroxyethylcellulose HEC/0.5 x Tris-borate-EDTA (TBE) solutions and dilute HEC/0.5 x TBE solution by high-speed video microscopy. Measurements were made microscopically over a short migration distance in homogeneous DNA HEC/0.5 x TBE solution and after electrophoretic migration of a plug of DNA through 7 cm. Video at 120 frames/s (semidilute HEC solution) and 236 frames/s (dilute HEC solution) allowed visualization with adequate resolution for single molecule mobility measurements. The electrophoretic migration times and band shapes predicted from the measurements corresponded well with those measured by conventional capillary electrophoresis (CE) in both semidilute and dilute HEC. In semidilute solution, the band width predicted by a square root of time scaling is in good agreement with the results of conventional CE. However, in dilute solution the precision of the measurements was not good enough to allow scaled estimates of band widths. 相似文献
998.
The syntheses of the K-oxides and K-imine derivatives of benzo[b]phenanthro[2,3-d]thiophene and benzo-[b]phenanthro[3,2-d]thiophene are described. The parent hydrocarbons 1 and 2 were oxidized with osmium tetroxide and sodium metaperiodate, and the dialdehydes 12 and 18 so formed, cyclized to the corresponding epoxides 1a,12b-dihydrobenz[b]oxireno[9,10]phenanthro[2,3-d]thiophene ( 7 ) and 1a,12b-dihydrobenz-[b]oxireno[9,10]phenanthro[3,2-d]thiophene ( 13 ). Reaction of the oxiranes with sodium azide gave mixtures of azido-alcohols that, in turn, were transformed to the thiaarene imines 1a,12b-dihydro-1H-benz[b]azirino-[9,10]phenanthro[2,3-d]thiophene ( 8 ) and 1a,12b-dihydro-1H-benz[b]azirino[9,10]phenanthro[3,2-d]thiophene ( 14 ), respectively, with the aid of tri-n-butylphosphine. 相似文献
999.
GaAs has been subjected to fast neutron or electron irradiations up to doses of 2×1019 n cm–2 and 1019 e– cm–2 respectively and subsequently annealed to temperatures of 500°C. Infrared absorption spectra (20–700 cm–1), measured at 20 K, show that the induced one-phonon absorption depends on the nature of the radiation. Resonant modes, at 45 cm–1 and 119 cm–1, and a broad line at 328 cm–1 were found in neutron irradiated material, whereas in electron irradiated material only the 45 cm–1 feature was detected. These spectroscopic features are interpreted as vibrational modes arising from intrinsic defect centres. 相似文献
1000.
Acyl phosphate monoesters are intermediates in many biochemical acylation reactions, such as those involving aminoacyl adenylates. Benzoyl methyl phosphate, a typical acyl phosphate monoester, is slowly hydrolyzed in neutral solutions but reacts rapidly with amines. Since biochemical processes of acyl phosphate monoesters involve accelerated reactions with oxygen-centered nucleophiles, we sought catalysts for hydrolysis and methanolysis of benzoyl methyl phosphate to mimic the biochemical outcome. Lanthanide ions are particularly effective catalysts, accelerating reactions much more than comparable levels of magnesium ion. Detailed kinetic analysis of the hydrolysis reactions reveals formation of a 1:1 complex, followed by rapid reaction with a nucleophile. The hydroxide-dependent hydrolysis rate in the europium complex is about 10(5) times that of free substrate with hydroxide. A mechanism that accounts for the data and observed behavior involves bidentate coordination of the metal ion by the acyl phosphate through phosphate and carbonyl oxygens, lowering the energy of the tetrahedral addition intermediate and the associated transition states. The dependence of the metal ion catalyzed process on the concentration of hydroxide ion is consistent with coordinated hydroxide acting as a nucleophile. The reaction of benzoyl methyl phosphate with methanol to form methyl benzoate and methyl phosphate is 30 000 times more rapid in the presence of 0.0001 M lanthanum triflate (in the absence of the metal ion k(obs) = 2.1 x 10(-7) s(-1), at 25 degrees C). Thus, the combination of acyl phosphate esters and lanthanide salts appears to be a promising method for biomimetic acylation of hydroxyl groups. 相似文献