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A series of substituted 4‐methylphenols 1 and 2 was oxidized with PbO2 in the presence of nitroso compounds 3 – 10 . The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H‐atom from the methyl substituent of 1 or 2 . In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky tBu groups in ortho‐position (see 2,6‐di(tert‐butyl)‐4‐methylphenol ( 1a )), the stable 2,6‐di(tert‐butyl)‐4R‐phenoxy radicals (R=? CH?N+(O?)? X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO radicals.  相似文献   

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Free radicals generated by UV‐light irradiation of a frozen solution containing a fraction of pyruvic acid (PA) have demonstrated their dissolution dynamic nuclear polarization (dDNP) potential, providing up to 30 % [1‐13C]PA liquid‐state polarization. Moreover, their labile nature has proven to pave a way to nuclear polarization storage and transport. Herein, differently from the case of PA, the issue of providing dDNP UV‐radical precursors (trimethylpyruvic acid and its methyl‐deuterated form) not involved in any metabolic pathway was investigated. The 13C dDNP performance was evaluated for hyperpolarization of [U‐13C6,1,2,3,4,5,6,6‐d7]‐d ‐glucose. The generated UV‐radicals proved to be versatile and highly efficient polarizing agents, providing, after dissolution and transfer (10 s), a 13C liquid‐state polarization of up to 32 %.  相似文献   

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In support of a research program aimed at discovering purine‐related anticancer drug candidates, a method for the 14C‐labeling of pyrazolopyrimidines utilizing the readily available labeled starting material, sodium [14C]formate, has been developed with a good overall yield. This new method was proven to be general in the preparation of other related [4.3.0]heterocycles containing N, O, and S atoms. A concise synthesis of a model compound, 8‐aza‐7‐deaza‐5′‐[14C]noraristeromycin, was achieved utilizing this methodology as a key step.  相似文献   

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A one‐pot method for consecutive Konoevenagel condensation, Michael addition, cyclization, dehydrogenation, and Ullmann coupling of 2‐halogenated aromatic aldehyde, 1H‐benzo[d ][1,2,3]triazol‐5‐amine, and cyclohexane‐1,3‐diones is presented. This procedure provided an efficient synthesis of fused hexacyclic quinolinotriazoloacridinone derivatives in good yields catalyzed by CuI/L‐proline.  相似文献   

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Three‐ and five‐membered rings that bear the (Si‐C‐S ) and (Si‐C‐C‐C‐S ) unit have been synthesized by the reactions of L SiCl ( 1 ; L =PhC(NtBu)2) and L′ Si ( 2 ; L′ =CH{(C?CH2)(CMe)(2,6‐iPr2C6H3N)2}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with L SiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3 . However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4 . Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si resulted in products 4 and 5 , in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C? S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.  相似文献   

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An efficient NaNO2/I2‐mediated one‐pot transformation of Morita–Baylis–Hillman (MBH) acetates into alkyl 3‐nitro‐5‐(aryl/alkyl)isoxazole‐4‐carboxylates is described. In a cascade event, initial Michael addition of NaNO2 to the MBH acetate furnishes the allylnitro intermediate which undergoes I2‐catalyzed oxidative α‐C H nitration of the nitromethyl subunit followed by [3+2] cycloaddition to afford the title compounds. Structural elaborations of these highly substituted isoxazoles by SNAr reactions and hydrogenolysis allows access to useful products.  相似文献   

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High‐spin FeII–alkyl complexes with bis(pyridylimino)isoindolato ligands were synthesized and their paramagnetic 1H and 13C NMR spectra were analyzed comprehensively. The experimental 13C—1H coupling values are temperature (T?1)‐ as well as magnetic‐field (B2)‐dependent and deviate considerably from typical scalar 1JCH couplings constants. This deviation is attributed to residual dipolar couplings (RDCs), which arise from partial alignment of the complexes in the presence of a strong magnetic field. The analysis of the experimental RDCs allows an unambiguous assignment of all 13C NMR resonances and, additionally, a structural refinement of the conformation of the complexes in solution. Moreover the RDCs can be used for the analysis of the alignment tensor and hence the tensor of the anisotropy of the magnetic susceptibility.  相似文献   

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