1,3-Dioxa-[3,3]-sigmatropic Oxo-Rearrangement of Substituted Allylic Carbamates: Scope and Mechanistic Studies
作者:Maddalen Agirre、Sylvain Henrion、Ivan Rivilla、José I. Miranda、Fernando P. Cossío、Bertrand Carboni、José M. Villalgordo、François Carreaux
DOI:10.1021/acs.joc.8b01320
日期:2018.12.21
alkenyl-substituted allylic alcohols with activated isocyanates is reported. The reorganization of bonds is highly dependent on the electron density of the aromatic ring and the nature of isocyanate used. This metal-free tandem reaction from branched allyl alcohols initiated by a carbamoylation reaction and followed by a sigmatropic rearrangement thus offers a new access to (E)-cinnamyl and conjugated (E,E)-diene
Orientations of the 17O electric-field-gradient tensor and chemical shift tensor in benzamide: NMR of dipolar coupled spins
作者:Gang Wu、Shuan Dong
DOI:10.1016/s0009-2614(00)01463-9
日期:2001.2
report a solid-state NMRstudy of [] benzamide. The orientations of the 17O electric-field-gradient and chemical shift tensors were determined from analysis of magic-angle spinning and stationary 17O NMR spectra. The largest electric-field-gradient component lies in the amide plane and perpendicular to the 13C–17O dipolar vector, whereas the intermediate electric-field-gradient component is along the
Solid-State <sup>17</sup>O NMR Investigation of the Carbonyl Oxygen Electric-Field-Gradient Tensor and Chemical Shielding Tensor in Amides
作者:Kazuhiko Yamada、Shuan Dong、Gang Wu
DOI:10.1021/ja0008315
日期:2000.11.1
oxygen electric-field-gradient (EFG) tensor and chemicalshielding (CS) tensor in crystalline amides. Three 17O-labled secondary amides, R1C[17O]-NHR2, have been synthesized: benzanilide (1), N-methylbenzamide (2), and acetanilide (3). Analysis of 17O magic-angle spinning (MAS) and stationary NMR spectra yields not only the magnitude but also the orientation of the carbonyl 17O EFG and CS tensors. For
Solid-State <sup>17</sup>O NMR Study of Carboxylic Acid Dimers: Simultaneously Accessing Spectral Properties of Low- and High-Energy Tautomers
作者:Gang Wu、Ivan Hung、Zhehong Gan、Victor Terskikh、Xianqi Kong
DOI:10.1021/acs.jpca.9b07224
日期:2019.9.26
We report a solid-state 17O NMRstudy of several crystalline carboxylicacids. We found that, while each of these compounds forms discrete hydrogen-bonded dimers in the crystal lattice, their solid-state 17O magic-angle spinning (MAS) NMR spectra display quite different features and different temperature dependencies. We showed that experimentally observed 17O NMR spectral behaviors can be explained
我们报告了几种结晶羧酸的固态17 O NMR研究。我们发现,尽管这些化合物均在晶格中形成离散的氢键二聚体,但它们的固态17 O魔角旋转(MAS)NMR光谱显示出完全不同的特征和不同的温度依赖性。我们表明,实验观察到的17 O NMR光谱行为可以解释为由于两个互变异构体之间的热平均,该互变异构体是由于每个二聚体中一致的双氢跳跃动力学而产生的。通常,由于分子内相互作用和晶体堆积,两个互变异构体具有不同的能量。从变温分析17在MAS NMR光谱中,对于所研究的每种羧酸化合物,通过实验确定了两个互变异构体之间的能量不对称性。相同的数据分析还提供了同时评估低能和高能互变异构体中17 O NMR参数的机会。我们得出的结论是,周期平面波密度泛函理论(DFT)计算可以为两个互变异构体产生可靠的17 O NMR参数(化学位移和四极耦合张量)。相同的定期DFT计算也为所研究的羧酸二聚体产生了合理的能量不对称值。我们还观察到固态17
On the detection of both carbonyl and hydroxyl oxygens in amino acid derivatives: a 17O NMR reinvestigation
作者:Vassiliki Theodorou、Anastassios N. Troganis、Ioannis P. Gerothanassis
DOI:10.1016/j.tetlet.2003.12.162
日期:2004.3
The hypothesis and the conclusions of previous O-17 NMR studies on the detection of both oxygens of the carboxylic group of Boc-[O-17]Tyr(2,6-diClBzl)-OH in DMSO-d(6) solution (V. Tsikaris et al., Tetrahedron Lett. 2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the O-17 NMR time scale. (C) 2004 Elsevier Ltd. All rights reserved.