使用在负载的银催化剂上生成的有机硝基盐将伯羟基区域选择性氧化为羧酸,这会促进水溶液中2,2,6,6-四甲基哌啶基-1-氧基(TEMPO)歧化。氧化反应是在室温下在间歇式反应器中于pH 9.5下进行的,反应中使用了非均相的银催化剂和过氧化物作为主要的助氧化剂。例如,使用碳酸银-硅藻土催化剂在吡喃糖苷的90%转化率下获得对甲基-α-D-吡喃葡萄糖醛酸的99 mol%选择性。通过向银催化剂中添加碳酸盐来提高系统的效率。该结果由存在碳酸盐时银上电子电荷不足的增加解释,这加速了羟基和/或TEMPO的亲核攻击。2 O 3催化剂,该结果通过使用氨的程序升温脱附测量得到了证明。对于伯/仲多元醇,伯羟基的选择性高。另外,与吡喃糖苷一样,伯羟基的氧化比呋喃糖苷的伯羟基更选择性地被氧化。观察到的区域选择性是由于TEMPO中的四个甲基引起的空间位阻。
Synthesis, characterization, density function theory and catalytic performances of palladium(II)–N-heterocyclic carbene complexes derived from benzimidazol-2-ylidenes
作者:Abbas Washeel Salman、Ghani Ur Rehman、Norbani Abdullah、Srinivasa Budagumpi、Salasiah Endud、Hassan H. Abdallah
DOI:10.1016/j.ica.2015.08.027
日期:2015.11
Subsequent reactions of the silver(I) halide/hexafluorophosphatecomplexes with [PdCl2(CNCH3)2] in methanol afforded the NHC palladium(II) complexes (5 and 6) via carbene transfer method. All synthesized compounds were fully characterized by analytical and spectrometric methods. Preliminary catalytic studies evinced that the nitrile-functionalized palladium(II)-NHC complex6 is highly active in the oxidation
stability of these superiron cathodes. However, for an Fe(VI) salt, which is not stable in the solid state, such as BaFeO 2 , an applied zirconia coating is not observed to stabilizealkaline cathodic chargetransfer. Small particle and solid KOH and AgO additives each are observed to improve Fe(VI) cathodic chargetransfer and enhance accessible Fe(VI) gravimetric capacity.
thermal stability/reducibility of metal nitrates in an hydrogen atmosphere has also been studied by temperature-programmed reduction (TPR). Observed reduction temperatures (Tr) for nitrates of the base metals and the noble metals are lower than their Td, i.e., Tr < Td. The lowering of Tr might be attributed to a spillover of hydrogen to a nitrate moiety through heterolytic (ionic) and homolytic (atomic)
medicinal plants. These isoprenoids exhibit a broad range of biological activities, such as antitumor and antiplasmodial activities. Here, we report the collective totalsynthesis of perovskone, perovskones C, D, F, hydrangenone, and hydrangenone B. The key strategies in this work include the following: (1) an asymmetric photoenolization/Diels–Alder reaction was developed to construct a tricyclic ring bearing
Perovskones 和 hydrangenones 是结构复杂的三萜类化合物家族,主要从丹参属药用植物中分离出来。这些类异戊二烯表现出广泛的生物活性,例如抗肿瘤和抗疟原虫活性。在这里,我们报告了 perovskone、perovskone C、D、F、hydrangenone 和 hydrangenone B 的集体全合成。 这项工作的关键策略包括:(1)不对称光烯醇化/Diels-Alder 反应被开发来构建一个带有三个连续四元中心的三环环,用于构建核心icetexane骨架;(2) 受生物启发的钙钛矿 D 与反式的Diels-Alder 反应-α-罗勒烯被应用于立体定向生成钙酮;(3) 开发了后期氧化和成环步骤来合成钙酮和氢化物酮。我们的合成工作表明:(1)钙酮 D 可能作为钙酮生物合成的前体;(2)含有五元 D 环的三氢醌和三氢醌 B 的形成可能涉及氧化环裂解和环再生过程.
Expanded Ring NHC Silver Carboxylate Complexes as Efficient and Reusable Catalysts for the Carboxylative Cyclization of Unsubstituted Propargylic Derivatives
作者:Alejandro Cervantes‐Reyes、Tobias Saxl、Philipp M. Stein、Matthias Rudolph、Frank Rominger、Abdullah M. Asiri、A. Stephen K. Hashmi
DOI:10.1002/cssc.202002822
日期:2021.6.8
α-methylene cyclic carbonates. Derivedfrom X-ray diffraction studies, the molecular geometry and the concept of buried volume were employed to describe the structural and steric features of these silver complexes. Their stability and efficiency as catalysts have been demonstrated by the synthesis of 29 carboxylation products (72–98 % yield) at low catalyst loadings (0.01–1.5 mol%). Characteristics are high