5018-27-9Relevant articles and documents
A substituent- And temperature-controllable NHC-derived zwitterionic catalyst enables CO2upgrading for high-efficiency construction of formamides and benzimidazoles
Li, Hu,Li, Zhengyi,Wu, Hongguo,Yang, Song,Yu, Zhaozhuo,Zhang, Lilong,Zhu, Kaixun
supporting information, p. 5759 - 5765 (2021/08/23)
Chemocatalytic upgrading of the greenhouse gas CO2 to valuable chemicals and biofuels has attracted broad attention in recent years. Among the reported approaches, N-formylation of CO2 with an amine is of great significance due to its versatility in the construction of N-containing linear and cyclic skeletons. Herein, a stable N-heterocyclic carbene-carboxyl adduct (NHC-CO2) was facilely prepared and could be used as a recyclable zwitterionic catalyst for efficient CO2 reductive upgrading via either N-formylation or further coupling with cyclization under mild conditions (25 °C, 1 atm CO2) using hydrosilane as a hydrogen source. More than 30 different alkyl and aromatic amines could be transformed into the corresponding formamides or benzimidazoles with remarkable yields (74%-98%). The electronic effect of the introduced substituent on NHC-CO2 was found to evidently affect the thermostability and nucleophilicity of the zwitterionic catalyst, which is directly correlated with its catalytic activity. Moreover, NHC-CO2 could supply CO2 by in situ decarboxylation at a specific temperature that is dependent on the introduced substituent type. Experimental and computational studies showed that the carboxyl species on NHC-CO2 was not only a nucleophilic center, but also a C1 source which rapidly captures or substitutes ambient CO2 during hydrosilylation. In addition, a simple and green conceptual process was designed for the product purification and catalyst recycling, with a good feasibility for small-scale production.
Synthesis of [3-13C]-, [4-13C]- and [11- 13C]-porphobilinogen
Dawadi, Prativa B. S.,Schulten, Els A. M.,Lugtenburg, Johan
experimental part, p. 341 - 349 (2011/07/08)
[4-13C]-porphobilinogen 1a, [3-13C]-porphobilinogen 1b and [11-13C]-porphobilinogen 1c are prepared from [1- 13C]-3-(tetrahydropyran-20-yloxy)-propionaldehyde 2a, methyl [4- 13C]-4-nitrobutyrate 3b and [1-13C]-isocyanoacetonitrile 5c, respectively. The building blocks 2, 3 and 5 can be prepared efficiently in any isotopomeric form. Via base-catalyzed condensation of these building blocks porphobilinogen can be enriched with 13C and 15N stable isotopes at any position and combination of positions. Copyright
Novel Benzodiazepine Receptor Partial Agonists: Oxadiazolylimidazobenzodiazepines
Watjen, Frank,Baker, Raymond,Engelstoff, Mogens,Herbert, Richard,MacLeod, Angus,et al.
, p. 2282 - 2291 (2007/10/02)
The synthesis and biochemical evaluation of a series of oxadiazole derivatives of imidazobenzodiazepines related to the benzodiazepine antagonist Ro 15-1788 (2a) are reported.Although the oxadiazole ring is seen as an isosteric replacement for the ester linkage, significant differences in structure-activity trends were observed.Specifically, oxadiazoles 9-12 invariably had increased receptor efficacy (as witnessed by measurements of the GABA shift) relative to the corresponding ester.Additionally, and in direct contrast to the classical agonists such as diazepam, affinity for the benzodiazepine receptor was enhanced by a 7- rather than 8-halo substituent.The results are discussed in terms of a six-point receptor-binding model originally based on the X-ray structure of 2a.For comparison, the crystal structures of two representative oxadiazole derivatives, 10h and 12o, having a 6-oxo and 6-phenyl group, respectively, were determined and the data incorporated into a modified binding model to account for the greater efficacy of these compounds.It is concluded that the antagonist behavior of 2a relies upon the hydrogen-bond-acceptor properties of the ester carbonyl oxygen whereas for the oxadiazole series this site is localized at the imidazole nitrogen.
