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1.
Spectroscopic studies of the [1,5-15N2]-labelled title compounds demonstrate the presence of the yellow trans-anti,s-trans () and the red trans-syn,s-cis () isomers in solution. There is no experimental evidence supporting the postulated novel hydrogen bridge . 相似文献
2.
H.I.X. Mager 《Tetrahedron letters》1979,20(37):3549-3552
The pyrazine ring opening is proven by rearrangements leading to benzimidazoles , and . A 4a- to 10a-adduct isomerization ( → ) and the intermediacy of a carbonyl oxide are indicated by pyrimidine ring contractions into and , respectively. 相似文献
3.
The acid catalysed reaction of 4-oxa-homoadamantan-5-one () with benzene yielded a mixture of 4a-phenyladamantan-2-one (), the equatorial isomer' () and 2-phenyl-2,4-o- benzenoadamantane () A plausible reaction pathway for the occurrence of . is put forward. The structure of , was deduced from spectroscopic data and reaction of the proposed intermediate 2,4a-diphenyladamantan-2-ol () with acid. 2,4-o-Ben-zenoadamantane () is prepared likewise. 相似文献
4.
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
5.
The acid catalysed rearrangement of 8-methyl-pentacyclo(5.4.0.02,6.03,10.05,9)undecan-8-endo-o1 () to 3-methyl-(D3)-trishomocuban-4-o1 () provided the key step to the synthesis of the title compound (). 相似文献
6.
W.David Ollis Julia Stephanidou Stephanatou J.Fraser Stoddart Gulten G. Unal David J. Williams 《Tetrahedron letters》1981,22(23):2225-2228
An X-ray structure analysis shows that the 5, 18-dimethyl derivative () of the title compound () crystallises from xylene as a 1:1 inclusion compound in which the host molecules adopt propeller-like conformations ( and *) with almost perfect 2 symmetry. Dynamic 1H n.m.r. spectroscopy shows that the 5, 18-dibenzyl derivative () of () forms a 1:1 inclusion compound with ethanol in the solid state and undergoes ring inversion ( ? *) between enantiomeric propeller-like conformations in solution against a barrier of 21.1 kcal mol?1 相似文献
7.
Reactions of C7F15Br with elemental fluorine at 0°C have produced perfluoro--heptylbromine(V) tetrafluoride (-C7F15BrF4). This derivative of BrF5 was characterized by IR, 19FNMR, mass spectroscopy and elemental analysis. The reactions of C7F15BrF4 with 1,2-dichlorohexafluorocyclopentene-1 (C5F6Cl2) and 1,2-dichlorooctafluorocyclohexene-1 (C6F8Cl2) were used to demonstrate in the fluorinating ability of C7F15BrF4. 相似文献
8.
《Tetrahedron》1986,42(20):5739-5746
Substrates such as () undergo regiospecific attack by azide and thiocyanate ions at the terminus of the CC-CN-CO system. In the case of addition of azide, this is proved by the detailed analysis of the 1H and 13C NMR spectra of the products () derived from the quinone-imides (). The structure of the products obtained by the addition of thiocyanate to the quinone-imides and ()() is proved by their facile cyclisation to the 2-aminobenzothiazoles () and () respectively. 相似文献
9.
L.J. Goad F.-X. Garneau J.-L. Simard J.W. ApSimon M. Girard 《Tetrahedron letters》1985,26(29):3513-3516
- 14α-Methyl-5α-cholest-9(11)-en-3β-ol () and 4α,14α-dimethyl-5α-cholest-9(11)-en-3β-ol () have been isolated from the sea cucumber and characterised by 1H NMR, 13C NMR and mass spectrometry. Lanost-9(11)-en-3β-ol () has also been tentatively identified. The relevance of this series of Δ9(11)-sterols to holothurin biosynthesis is briefly discussed. 相似文献
10.
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
11.
The model tripeptide Boc-Gly-S-Ala-Aib-OMe () and the two monothiated analogues Boc-Gly(1ψ2CSNH)-S-Ala-Aib-OMe () and Boc-Gly-S-Ala(2ψ3 CSNH)-Aib-OMe () were synthesized. Peptide was obtained by thiation of using 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, Lawesson's Reagent (LR), followed by deprotection of the Boc group and coupling with Boc-Gly-OH. Thiation of with LR regiospecifically transformed the protected tripeptide to the monothiated analogue . X-Ray diffraction analysis showed that the type-III β-turn formed by the reference peptide is preserved in the monothiated analogue ; conversely,the structure of the isomeric tripeptide is partially extended. 相似文献
12.
Shinichi Uesato Shinichi Ueda Koji Kobayashi Masao Miyauchi Hiroyuki Inouye 《Tetrahedron letters》1984,25(5):573-576
Administration of 2H- or 13C-labeled monoterpenes to f. cell suspension cultures demonstrated that iridoid glucosides of the suspension cultures are biosynthesized, after iridodial cation formation from 10-oxocitral (3), via 8-epiiridodial (13), 8-epiiridotrial (14), boschnaloside (8-epiiridotrial glucoside) (12) and dehydroiridotrial glucoside (8). In addition, the coexistence of a route via iridodial cation (4), dehydroiridodial (6), dehydroiridotrial (15) and dehydroiridotrial glucoside (8) is conceivable. 相似文献
13.
The photochemical reactions of tetracyclic azo compounds () giving and via diazoethane derivatives () were investigated in addition to the nitrogen extrusion reactions leading to tetracyclo[4.3.0.02,9.05,7nonenes (). 相似文献
14.
Vacuum UV emission from the products of quenching ofAr(3Po) and Ar(3P2) by several reagents has been compared. The large differences suggest that Ar(3Po) and Ar(3P2) preferentially yield respectively the D() and B() excited states of ArBr★ or ArCl★, which show specific, but very different, predissociation patterns. 相似文献
15.
A novel approach to (±)-epipodophyllotoxin () and hence also (±)-podophyllotoxin () is described, involving as a key-step the stereoselective ring closure of the TMS-ester derived from to the tetralin derivative with mesyl chloride. 相似文献
16.
Dehydrotripeptides, X-CH(Ri)-ΔPhe-CH(Rk)COOMe (: X = tBOC-NH,CBZ-NH, CF3CONH and N3), were employed for the asymmetric hydrogenation catalyzed by chiral rhodium complexes and it was found that tBOC- brought about by far the best results. Stereoselective dideuteration of a tBOC- was successfully performed. 相似文献
17.
The details and principles of an apparatus built for measurements of fluorescence quantum yields and cascade-free lifetimes of open-shell cations are reported. These rely on the detection of coincidences between energy selected photoelectrons and undispersed photons. The results of such measurements for CO+2, COS+, CS+2 and N2O+ in selected vibrational levels of their excited states are presented. Non-unity fluorescence quantum yields are found for some vibronic levels of CO+2(), COS+ (), N2OP+() and a non-exponential decay is observed for CS+2(). The data yield the following values for the radiative lifetimes: CO+2() 124 ± 6 ns, CO+2() 140 ± 7 ns, COS+() 550 ± 50 ns and N2O+() 240 ± 12 ns. 相似文献
18.
Felix H. Cano Concha Foces-Foces Manuel Bernabe Jesus Jimenez-Barbero Manuel Martin-Lomas Soledad Penades-Ullate 《Tetrahedron》1985,41(18):3875-3886
X-Ray and 1H N.M.R. studies on pyranoid rings 1,2--fused to dioxolane rings in acetylated -gluco- and --galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the -gluco but not in the -galactopyranose series. The crystal structure of 3,4,6-tri--acetyl-1,2--(R)--(l-cyano-ethylidene)-α--glucopyranose () and 3,4,6-tri--acetyl-1,2--()-(1-cyano-ethylidene)-α--galactopyranose ()have been determined by X-ray analysis. Lattice parameters for are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened 4C1 and that of the dioxolane ring as distorted E1. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The 1H N.M.R. spectra of and and 3,4,6-tri--acetyl-1,2-O-(S)- and (R)-ethylidene-α--glucopyranose ( and ), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ()-ethylidene-α--galactopyranose ( and ), and 3,4,6-tri--acetyl-1,2--()-and ()-benzylidene-α--glucopyranose ( and ) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the -gluco series , and may be described as flattened 4C1 and that of and as 25. The major solution conformation of the pyranoid ring in all compounds in the -galacto series (,,,) may be described as flattened 41. 相似文献
19.
At low temperatures, the 19F n.m.r. spectrum of the tetrazan (CF3)2NN(CF3)N(CF3)N(CF3)2 shows the presence of two isomers with a free energy difference in stability Δ of 2.2 kJ mol-1. Both isomers show three types of CF3 group which coalesce at -15°C to three systems of equal intensity (Δ≠ 52 kJ mol-1). At 40 °C the two signals assigned to the terminal CF3 groups coalesce to a single band (Δ≠ 65 kJ mol-1).The behaviour is discussed in terms of restricted inversion at the nitrogen atoms, and hindered rotation about the N-N bonds.The hydrazines (CF3)2NN(CF3)NO and (CF3)2NN(CF3)NO2 have temperature independent spectra. 相似文献
20.
Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(2P) + O2 → Br(2P) + O2 (k1), and Br(2P) + NO → Br(2P) + NO (k4) have been measured with a photodissociative IBr laser on the electronic transition 2P?2P in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10?14 cm3 s?1 and (1.9 ± 0.6) × 10?12 cm3 s?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher. 相似文献