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151.
The photolysis of five N‐arylbenzamidoxime derivatives I‐V in dry acetonitrile gives rise to anilides 8 and benzimidazoles 1 as the major products in addition to benzonitrile 4 , arylamines 5 , benzoic acid 6 , and 2‐phenyl benzoxazoles 7 . In the presence of naphthalene, I gave α‐ and β‐naphthols 2 and 3 beside the previous products. The isolated products have been interpreted in the terms of a free radical mechanism involving the homolysis of N‐O and/or C‐N bonds. This photodegradation process can be considered as an alternative method for the synthesis of anilide, benzimidazole and benzoxazole derivatives in addition to other organic compounds. 相似文献
152.
Photoinduced [3+2] Cycloaddition of Carbenes and Nitriles: A Versatile Approach to Oxazole Synthesis
Argha Saha Chiranjit Sen Srimanta Guin Chandan Das Debajit Maiti Prof. Dr. Subhabrata Sen Prof. Dr. Debabrata Maiti 《Angewandte Chemie (International ed. in English)》2023,62(48):e202308916
We have developed a photoinduced protocol for the synthesis of pharmaceutically important oxazole molecules using diazo- and nitrile-containing reactants. The process involves the initial photolysis of the diazo compound to afford singlet carbenes, which are tapped by nitriles in a [3+2] cycloaddition fashion to give substituted oxazoles. With di-nitrile compounds, useful bis-oxazoles were obtained. The applicability of the transformation is showcased through the expedient synthesis of small-molecule drugs and biologically relevant molecules such as felbinac, pimprinine, texamine, ugnenenazole etc. The protocol is also useful for the generation of 2H and 13C isotope labelled oxazoles. Merging photolysis with continuous-flow chemistry was demonstrated for scaling up the reaction. The non-requirement of metal catalysis or photosensitizers to harness the light energy with blue light sufficing the execution of the reaction makes it a versatile and general protocol for the synthesis of structurally diverse oxazoles 相似文献
153.
Harir M Frommberger M Gaspar A Martens D Kettrup A El Azzouzi M Schmitt-Kopplin P 《Analytical and bioanalytical chemistry》2007,389(5):1459-1467
The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts
from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact
mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method
comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking
care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation
of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise
formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox.
Figure Overview of applied method to analyse the photolysis process of imazamox herbicide 相似文献
154.
Jennifer Fedorowski 《Analytica chimica acta》2010,657(1):1-35
Post-column photochemical reaction systems have developed into a common approach for enhancing conventional methods of detection in HPLC. Photochemical reactions as a means of ‘derivatization’ have a significant number of advantages over chemical reaction-based methods, and a significant effort has been demonstrated to develop an efficient photochemical reactor. When coupled to electrochemical (EC) detection, the technique allows for the sensitive and selective determination of a variety of compounds (e.g., organic nitro explosives, beta-lactam antibiotics, sulfur-containing antibiotics, pesticides and insecticides). This review will focus on developments and methods using post-column photochemical reaction systems followed by EC detection in liquid chromatography. Papers are presented in chronological order to emphasize the evolution of the approach and continued importance of the application. 相似文献
155.
Abstract Aerated benzene solutions containing anthracene together with one of the carotenoids, β-carotene, β-apo-8′-carotenal, ethyl β-apo-8′-carotenate and canthaxanthin were subjected to laser photolysis. Under these conditions oxygen quenching of triplet anthracene produces the excited singlet state of molecular oxygen O2? (1δg) which in turn transfers energy to the carotenoid thereby yielding its triplet state, the absorption of which was monitored thereby confirming electronic energy transfer as the mechanism of quenching of O2 ?(1δg) by these carotenoids and enabling the bimolecular quenching constansts which vary from 1.2 – 1.45 × 1010 1 mol?1s?1 to be measured. 相似文献
156.
Keitaro Ishii Takuya Sone Takahide Shigeyama Masahiro Noji Shigeo Sugiyama 《Tetrahedron》2006,62(47):10865-10878
The photochemical C,C-bond cleavage of trisubstituted aziridines 3-6 and consequent [3+2] cycloaddition with electron-deficient alkenes afforded the novel head-to-head adducts (1,2,3,5-tetrasubstituted pyrrolidines) selectively and efficiently. The aziridines 3 and 5 reacted with molecular oxygen, affording dioxazolidine 26 and cleaved products, respectively. The results may suggest that the C,C-bond of aziridine cleaves biradically. The photoreactions of N-tritylaziridines 7-9 possessing diester, dinitrile, and butadiene groups in the side chain with electron-deficient alkenes yielded 2,3-cis-pyrrolidine derivatives 29, 30, and 33 exclusively. In particular, the dinitrile 8 also reacted with non-electron-deficient alkenes. The formal synthesis of the indolizidine fragment 10 of stellettamides starting from the pyrrolidine (E)-33 was achieved in a convenient manner. 相似文献
157.
Xin Zhang 《Journal of organometallic chemistry》2006,691(4):659-666
A series of μ-polymethylene bridged dicobaloxime complexes py(dmgH)2Co(CH2)nCo(dmgH)2, where n = 4, 5, 6, and 12 (1-4) were synthesized and characterized. Crystal structures of py(dmgH)2Co(CH2)4Co(dmgH)2py · 2CH2Cl2 (1 · 2CH2Cl2), py(dmgH)2Co(CH2)5Co(dmgH)2py (2), and py(dmgH)2Co(CH2)6Co(dmgH)2py · CH2Cl2 (3 · CH2Cl2) have been determined by X-ray diffraction. Their structural features are compared with those reported for monocobaloxime complexes and oligomethylene-bridged vitamin B12 dimer. 2-D layers or 3-D nets formed through intermolecular C-H?O interactions are observed in the molecular packing structures of 1 · 2CH2Cl2, 2, and 3 · CH2Cl2. The photolytic kinetic rates of the dicobaloximes were determined by UV-Vis spectroscopy and the products of photolytic solutions were characterized by ESI-MS. The results indicated that lengths of polymethylene have a little effect on the observed rate of the Co-C bond cleavage in our dicobaloxime complexes, while changing the solvent from methanol to ethanol has shown significant rate enhancement. In addition, TGA experiments for solid dicobaloxime complexes were performed to exam their thermal decomposition behaviors. 相似文献
158.
159.
《Journal of Coordination Chemistry》2012,65(11):1743-1753
Broadband (λ > 320 nm) irradiation of chloroform solutions of either [Ru(bpy)2Cl2] or [Ru(bpy)2Cl2]Cl exposed to air led to a photostationary state, in which [Ru(bpy)2Cl2]+ predominated, and to the continuous decomposition of CHCl3, as evidenced by the accumulation of HCl, hydroperoxides (CCl3OOH and CHCl2OOH), and tetra-, penta-, and hexachloroethane. The addition of Cl? increased the rate of photodecomposition, while the replacement of Cl? by F? greatly decreased the rate. The observations are consistent with a photocatalytic cycle in which [Ru(bpy)2Cl2]+ is photochemically reduced to [Ru(bpy)2Cl2], which is thermally reoxidized by CCl3OO or CCl3OOH. In the absence of air a much slower photodecomposition reaction takes place leading to continuously increasing concentrations of chloroethanes. The data are consistent with a catalytic cycle in which [Ru(bpy)2Cl2]+ is photoreduced, as in aerated solutions, while [Ru(bpy)2Cl2] is photooxidized with chloroform as the substrate. 相似文献
160.
本文用自旋捕捉剂亚硝基叔丁烷(MNP)和2,3,5,6-四甲基亚硝基苯与ESR相结合分别研究了N-溴代琥珀酰亚胺(NBS)光解反应产生的自由基,以及NBS与醇、取代芳烃及烷烃进行光解夺氢反应生成的活泼自由基中间体,结果表明:1.在紫外光用下,NBS分子中的N-Br键发生均裂,产生N-中心自由基并为MNP所捕获.2.对于醇及烷烃,NBS光解产生的Br能夺取叔碳原子上的氢,分别形成叔碳自由基HOR和R,并被ND所捕获.3.与烷烃及醇不同的是:Br不仅能夺取烷基取代苯分子中叔碳原子上的氢,而且还能夺取仲碳原子上的氢,分别形成自由基PhCR2及PhCHR. 相似文献