共查询到20条相似文献,搜索用时 15 毫秒
1.
The a4 umpolung of α-allenic ketone sis performed using the triphenylphosphonio group. It results in inducing an electrophilic character at the carbon ψ to the carbonyl function and in changing the regioselectivity of the additions of active hydrogen compounds on the carbon-carbon double bond to give finally the adducts (Fig. 1).This new umpolung method is illustrated here in the case of the addition of methanol on allenyl methyl ketone (Fig. 2). 相似文献
2.
By preparing following a route of known stereochemistry, we were able to elucidate the stereochemistry of the conversion of the levorotatory bromoallene into levorotatory by -Bu(CN)CuLi: the reaction occurs with retention of configuration in the allenyl moiety. 相似文献
3.
Various furanosyl and pyranosyl fluorides react rapidly with alkyl, alkenyl, alkynyl, and aryl organoaluminum reagents at or below room temperature to form -glycosides in 68–93% yields. Effective application of this procedure to a 6-fluoro 1,6-anhydroglucose derivative produced a chain-extended sugar stereospecifically. 相似文献
4.
The preparation of the bicyclic alkenyl sulphoxides (n = 1 and 2; R = CH2CH3) from the alkynyl sulphenic acids is described. 相似文献
5.
Photooxygenations of 4-2H-anisole () and o-xylene () by 3-methylpyridazine 2-oxide () or pyridine 1-oxide () were studied in a variety of solvents at varying irradiation temperatures. Remarkable solvent effect on NIH-shift coupled with their hydroxylation processes was observed. 相似文献
6.
The production of I(2P) in the photolysis of CH2I2 has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm?1 correlate with I(2P) whilst those at 34700 and 40100 cm?1, which correlate with I(2P), give final 2P/2P ratios of 1.75 and 1.1, respectively, after curve crossing. 相似文献
7.
Simultaneous presence of the salt and one of the lanthanide complexes (+)-, (+)-, or (+)- splits 1H or 13C NMR signals of the chiral alkenes , , and as well as of the chiral arene ; the enantiomeric purity of a mixture of (+)- and (?)- was determined successfully. 相似文献
8.
Kenichi Takeuchi Toshikazu Kitagawa Akihiko Ueda Yoshihide Senzaki Kunio Okamoto 《Tetrahedron》1985,41(23):5455-5463
7-Cyano-7-methylcycloheptatrienes containing one t-butyl group on the 1-position () or two t-butyl groups on the 1- and 3-, 1- and 4-, or 1- and 5-positions (, , or , respectively) were synthesized and their cyclo- heptatriene (CHT)-norcaradiene (NCD) equilibria measured by variable-temperature 1H NMR for CS2-CD2Cl2 solutions. The 1H NMR chemical shifts of the 7-methyl group indicate that these compounds are composed of essentially one CHT and one NCD tautomer with an endo geometry of the methyl group. The introduction of a t-butyl group at the 1-position of 7-cyano-7-methylcycloheptatriene () markedly shifts the equilibrium to the NCD side and the addition of the second t-butyl group further favors the NCD form, with the NCD populations for , , , and at 25 °C 70.9, 96.5, 92.3, and 99.3%, respectively. An application of molecular mechanics (MMPI) calculations to various t-butylated CHT-NCD systems suggests that the t-butyl groups sterically destabilize the CHT form more than the NCD form, bringing about increased NCD populations. 相似文献
9.
R.D. Chambers P.A. Martin J.S. Waterhouse D.L.H. Williams B. Anderson 《Journal of fluorine chemistry》1982,20(4):507-514
Rate constants have been measured for the reactions of ammonia with various fluorinated pyridines and diazines in aqueous dioxan at 25°. From the results the activating effects of ring-nitrogen (relative to CH) and of trifluoromethyl (relative to -H) have been determined. Ring-nitrogen activates the system at points -, - and - to the point of substitution, in the ratios - 6.2 × 104, - 8.5 × 102, and - 2.3 × 105. Similarly a trifluoromethyl substituent is activating by a factor of 2.4 × 103- and 4.5 × 103- to the point of substitution. 相似文献
10.
C.C. Lee K.J. Demchuk W.J. Pannekoek R.G. Sutherland 《Journal of organometallic chemistry》1978,162(2):253-269
Ligand exchange reactions between phenanthrene or 9,10-dimethylphenanthrene with ferrocene effected in the presence of AlCl3-Al were carried out under a variety of conditions. With phenanthrene (I), hydrogenation at the C-9 and C-10 positions could take place during the reaction and the cationic products obtained were the η6-phenanthrene-η5-cyclopentadienyliron and η6-9,10-dihydro-phenanthrene-η5-cyclopentadienyliron moncations (II and III), and the η6-phenanthrene---η5-cyclopentadienyliron and η6-9,10-dihydrophenanthrene---η5-cyclopentadienyliron dications (IV and V). With 9,10-dimethylphenanthrene (VI), reactions carried out in refluxing cyclohexane gave the non-hydrogenated η6-9,10-dimethylphenanthrene-η5-cyclopentadienyliron monocation (VII) and η6-9,10-dimethylphenanthrene---η5-cyclopentadienyliron dication (VIII). When higher temperatures were used in an attempt to promote hydrogenation, decomposition predominated and no cationic product could be obtained. These finding are discussed and contrasted with previous results obtained from similar reactions using anthracene or 9,10-dimethylanthracene. 相似文献
11.
Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni 《Tetrahedron letters》1979,20(26):2453-2454
Feeding experiments with (4) [5-3H;5-14C]-leucine () and with the (4) [5-3H;2-14C]-isomer () show that incorporation into the isoprenylated tryptophan derivative echinuline (), produced by , involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid. 相似文献
12.
During the hydrogenation of the Δ3(3a)-4-hydrindenones or on Pd or Ni, we observe a shift of the double bond to Δ3a(7a)-4-hydrindenones and . The absolute configuration established for ketones and shows that the reaction is a suprafacial process. By deuteriation experiments, we observe that the reaction is irreversible and occurs with a molecular hydrogen exchange. 相似文献
13.
Leslie Crombie W.Mary L. Crombie Geoffrey W. Kilbee Patoomratana Tuchinda 《Tetrahedron letters》1979,20(49):4773-4776
4″-Carboxylated-cannabidiol,-Δ1-and-Δ1,6-tetrahydrocannabinols and - cannabinol are synthesised. Condensation between aromatic aldehydes and ethylidenemalonic ester gives a 2,4-half ester stereospecifically, a reaction which can be used to make 2-4- or 2,4-pentadienoates. 相似文献
14.
Ronald D. Brown Peter D. Godfrey Donald C. McGilvery Jonathan G. Crofts 《Chemical physics letters》1981,84(3):437-439
Microwave—optical double resonance signals have been detected in a mass-selected ion-beam spectrometer for 12C16O+. With the optical excitation of fluorescence from the R1 () line of the (0,0) band of the A2Π ← X2∑ transition of 20350.6 cm?1, the microwave resonances occurred at 118101.8 ± 0.2 MHz and at 117694 ± 2 MHz corresponding to the N= 1, J = ← N = 0, J = and the N = 1, J = ← N = 0, J = transitions. 相似文献
15.
A practical synthesis of [Ph3CH2F]BF4? is reported two routes, fluorination of [Ph3CH2OH]BF4? with DAST or hydrolysis of the phosphoranium salt, [Ph3FPh3]Br?. 相似文献
16.
John J. Eisch Robert J. Manfre David A. Komar 《Journal of organometallic chemistry》1978,159(4):C13-C19
A 1:1 combination of dichloro(bis-η5-cyclopentadienyl)titanium and alkyl-aluminum halide in methylene chloride solution effects the regiospecific alkylation of alkynyl(trimethyl)silanes in 60–95% yields. With RCCSiMe3 substrates, where Rsaturated alkyl group, the carbometallation (introduction of a methyl or an ethyl group) occurs regiospecifically and stereoselectively in a - manner, giving a 75:25 to a 90:10 ratio of isomers. When the R in RCCSiMe3 is phenyl or 1-cyclohexenyl, then a non-stereoselective carbometallation is observed (50:50 mixtures of isomers). These results, which are explicable in terms of the formation of the (C5H5)2Ti-R cation and its attack on the alkynylsilane, offer stereochemical evidence for a cationic initiating step in the polymerization of ethylene by homogeneous Ziegler-Natta catalysts. 相似文献
17.
The 1H and 13C nmr spectra of , -9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid, 3, in DMSO-d6 or alkaline D2O, clearly show that it exists in a --conformation with carboxyl groups, thus being the first case of - preference of a bicyclo[3.3.1] nonan-9-one due to the presence of ,-2,4- substituents. 相似文献
18.
19.
The conditions for the preparation and cyclisation of the title compounds are described. The stability of the intermediate lithio-thiacyclohexenes is shown to depend on the reaction conditions and the substituents R1-R4. The final products , and arise from via a [1.4] sigmatropic rearrangement, a [1.3]prototropic shift followed by a [2.3] sigmatropic rearrangement, or the elimination of lithium methanethiolate respectively. 相似文献
20.
Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs2NaSmCl6. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, 6H to cystal fi levels of 6H-, 6F-, 4G-, 4F,, 4I, and 6P, are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in 6H→6F - and 6P, transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm3+)-ligand (Cl?) interaction mechanisms. The Eu″(6H)→E′(6H) Eu′(6F) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs2NaSmCl6. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling Oh wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state. 相似文献