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81.
Polymer-supported dihydro[1,2]oxazine derivatives were prepared by acyl- and arylnitroso hetero-Diels-Alder reactions and exposed to strong (trifluoroacetic) acid during cleavage from resin-bound linkers. Cycloadducts prepared from cyclic dienes containing electron-donating substituents at the C6 oxazine carbon promoted formation of carbocations by cleavage of the C-O bond. The carbocations were quenched by nucleophilic reagents including triethylsilane, water, and alcohols and provided access to novel derivatives of N-alkyl hydroxamates. Products were submitted to biological assays, and the results are reported. 相似文献
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84.
Christoph O. Hollfelder Dr. Lars N. Jende Dr. Hans-Martin Dietrich Dr. Klaus Eichele Dr. Cäcilia Maichle-Mössmer Prof. Dr. Reiner Anwander 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(30):7298-7302
When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe2]3 (Ln=Y, Lu; Cp*=C5Me5) promote efficiently the formation of high-cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl. 1H DOSY). The occurrence of donor-solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe2]3 and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*3Y3Me4(CH2)(thf)2] and [Cp*6Y6Me4(CH2)4], as well as [(Cp*Y)2Me2(N(Me)2(C6H4)]n[B(C6F5)4]n, implying a multimetallic active species. 相似文献
85.
Scherlach K Brendel N Ishida K Dahse HM Hertweck C 《Organic & biomolecular chemistry》2012,10(30):5756-5759
Through metabolic profiling of mutants and wild type of the endofungal bacterium Burkholderia rhizoxinica two novel rhizoxin derivatives with unusual nitrile substitutions were discovered. The nitrile groups result from a photochemical oxidative cleavage of the oxazolyl moiety. In vitro studies revealed that the photooxidation by singlet oxygen also takes place in the absence of a photosensitizer, and that also a thiazolyl-substituted rhizoxin analogue undergoes the same transformation. The resulting nitriles have antimitotic properties but are significantly less active than the parent compounds. These results highlight the impact of photoreactions onto the antiproliferative agent and encourage the introduction of bioisosteric groups that render the compound less susceptible towards photooxidation. 相似文献
86.
Berends HM Manke AM Näther C Tuczek F Kurz P 《Dalton transactions (Cambridge, England : 2003)》2012,41(20):6215-6224
In this work the synthesis of the novel manganese complex [Mn(2)(III,III)(tpdm)(2)(μ-O)(μ-OAc)(2)](2+) (1) is reported, containing two manganese centres ligated to the unusual, facially coordinating, all-pyridine ligand tpdm (tris(2-pyridyl)methane). The geometric and electronic properties of complex 1 were characterised by X-ray crystallography, vibrational (IR and Raman) and optical spectroscopy (UV/Vis and MCD). Cyclic voltammograms of 1 showed a quasi-reversible oxidation event at 950 mV and an irreversible reduction wave at -250 mV vs. Ag/Ag(+). The redox behaviour of the compound was investigated in detail by UV/Vis- and X-band EPR-spectroelectrochemistry. Both electrochemical (+1200 mV) and chemical (tBuOOH) oxidations transform 1 into the singly oxidized di-μ-oxido species [Mn(2)(III,IV)(tpdm)(2)(μ-O)(2)(μ-OAc)](2+). Further electrochemical oxidation at the same potential results in the removal of a second electron to obtain a Mn(2)(IV,IV)-species. The ability of compound 1 to evolve O(2) was studied using different reaction agents. While reactions with both hydrogen peroxide and peroxomonosulfate yield O(2), homogeneous water-oxidation using Ce(IV) was not observed. Nevertheless, the oxidation reactions of 1 are very interesting model processes for oxidation state (S-state) transitions of the natural manganese water-oxidation catalyst in photosynthesis. However, despite its favourable coordination geometry and multielectron redox chemistry, complex 1 fails to be a catalytically active model for natural water-oxidation. 相似文献
87.
The S(1)<-->S(0) vibronic spectra of supersonic jet-cooled 2-pyridone [pyridin-2-one (2PY)] and its N-H deuterated isotopomer (d-2PY) have been recorded by two-color resonant two-photon ionization, laser-induced fluorescence and emission, and fluorescence depletion spectroscopies. By combining these methods, the B origin of 2PY at 0(0) (0)+98 cm(-1) and the bands at +218 and +252 cm(-1) are identified as overtones of the S(1) state out-of-plane vibrations nu(1) (') and nu(2) ('), as are the analogous bands of d-2PY. Anharmonic double-minimum potentials are derived for the respective out-of-plane coordinates that predict further nu(1) (') and nu(2) (') overtones and combinations, reproducing approximately 80% of the vibronic bands up to 600 cm(-1) above the 0(0) (0) band. The fluorescence spectra excited at the electronic origins and the nu(1) (') and nu(2) (') out-of-plane overtone levels confirm these assignments. The S(1) nonplanar minima and S(1)<--S(0) out-of-plane progressions are in agreement with the determination of nonplanar vibrationally averaged geometries for the 0(0) (0) and 0(0) (0)+98 cm(-1) upper states by Held et al. [J. Chem. Phys. 95, 8732 (1991)]. The fluorescence lifetimes of the S(1) state vibrations show strong mode dependence: Those of the out-of-plane levels decrease rapidly above 200 cm(-1) excess vibrational energy, while the in-plane vibrations nu(5) ('), nu(8) ('), and nu(9) (') have longer lifetimes, although they are above or interspersed with the "dark" out-of-plane states. This is interpreted in terms of an S(1) (') state reaction with a low barrier towards a conical intersection with a prefulvenic geometry. Out-of-plane vibrational states can directly surmount this barrier, whereas in-plane vibrations are much less efficient in this respect. Analysis of the fluorescence spectra allows to identify nine in-plane S(0) (') state fundamentals, overtones of the S(0) state nu(1) (") and nu(2) (") out-of-plane vibrations, and >30 other overtones and combination bands. The B3LYP6-311++G(d,p) calculated anharmonic wave numbers are in very good agreement with the observed fundamentals, overtones, and combinations, with a deviation Delta(rms)=1.3%. 相似文献
88.
89.
Experimental transmission profiles of 15 MeV electrons in silicon [111] have been measured. They show a fine structure which is not reproduced by a classical calculation. On the basis of the dynamical theory of diffraction a 331-beam calculation has been performed to interpret the experimental curves. 相似文献
90.
It is shown that in general it is not possible to differentiate between diphenyl methane derivatives (and compounds of analogous structure) substituted in o-position to the CH2-bridge and those carrying an m- or p-substituent by resorting solely to the ‘ortho-effect’ of the former. A rationale for this apparent anomaly is given. 相似文献