Vinyl Dihydropyrans and Dihydrooxazines: Cyclizations of Catalytic Ruthenium Carbenes Derived from Alkynals and Alkynones
作者:Fermín Cambeiro、Susana López、Jesús A. Varela、Carlos Saá
DOI:10.1002/anie.201400675
日期:2014.6.2
A novel synthesis of 2‐vinyldihydropyrans and dihydro‐1,4‐oxazines (morpholine derivatives) from alkynals and alkynones has been developed. The cyclizations require a mild generation of catalytic ruthenium carbenes from terminal alkynes and (trimethylsilyl)diazomethane followed by trapping with carbonyl nucleophiles. Mechanistic aspects of the new cyclizations are discussed.
Transition-Metal-Free Formal Decarboxylative Coupling of α-Oxocarboxylates with α-Bromoketones under Neutral Conditions: A Simple Access to 1,3-Diketones
作者:Zhen He、Xiaotian Qi、Shiqing Li、Yinsong Zhao、Ge Gao、Yu Lan、Yiwei Wu、Jingbo Lan、Jingsong You
DOI:10.1002/anie.201409361
日期:2015.1.12
A transition‐metal‐free formaldecarboxylativecoupling reaction between α‐oxocarboxylates and α‐bromoketones to synthesize 1,3‐diketone derivatives is presented. In this reaction, a broad scope of substrates can be employed, and neither a metal‐based reagent nor an additional base is required. DFT calculations reveal that this reaction proceeds through a coupling followed by decarboxylation mechanism
Multifold Bond Cleavage and Formation between MeOH and Quinoxalines (or Benzothiazoles): Synthesis of Carbaldehyde Dimethyl Acetals
作者:Yunkui Liu、Bo Jiang、Wei Zhang、Zhenyuan Xu
DOI:10.1021/jo302450f
日期:2013.2.1
2-quinoxalinyl (or 2-benzothiazolyl) carbaldehyde dimethyl acetals has been achieved. 2-Quinoxalinyl carbaldehyde dimethyl acetals were readily converted into 2-quinoxalinyl carbaldehydes in good to excellent yields under acidic conditions. Preliminary mechanistic studies suggest that the reaction proceeds via multifold bond cleavage and formation between methanol and N-heterocycles involving a dioxygen-participated
已经实现了由AK 2 S 2 O 8介导的喹喔啉(或苯并噻唑)与甲醇的直接交叉偶联反应,从而生成了2-喹喔啉基(或2-苯并噻唑基)甲醛二甲基乙缩醛。在酸性条件下,2-喹喔啉基甲醛二甲基乙缩醛易于以良好或优异的收率转化成2-喹喔啉基甲醛。初步的机理研究表明,该反应是通过多重键裂解和甲醇与N-杂环之间的形成而进行的,涉及双氧参与的自由基过程。该方法可以通过简单的N的交叉偶联直接合成各种2-喹喔啉基(或2-苯并噻唑基)甲醛二甲基乙缩醛。-在无醛,无酸和无过渡金属的条件下,杂环C–H键和甲醇。
Cleavage of lignin C–O bonds over a heterogeneous rhenium catalyst through hydrogen transfer reactions
作者:Bo Zhang、Zaojuan Qi、Xinxin Li、Jianwei Ji、Leilei Zhang、Hua Wang、Xiaoyan Liu、Changzhi Li
DOI:10.1039/c9gc01710k
日期:——
an important role in the cleavage of the C–O bonds. Notably, an ReOx/AC-catalyzed C–Obondcleavage pathway beyond a typical deoxydehydration mechanism was disclosed. More importantly, 2D-HSQC-NMR and GPC characterizations showed that ReOx/AC exhibited high activity not only in β-O-4 cleavage, but also in the deconstruction of more resistant β-5 and β–β linkages in lignin without destroying the aromatic
氢解是用于木质素解聚以生产芳香族化学品的最流行策略之一。当前,该策略主要在高氢气压力下进行,这会带来安全风险,并且不可持续且不经济。在本文中,我们报道了负载在活性炭上的异质氧化oxide(ReO x / AC)在异丙醇中木质素C–O键的选择性裂解中表现出出色的活性。在没有H 2的温和条件下,从各种木质素模型化合物中获得高产率的单酚(高达99.0%),从木质素原料中获得高产率的芳烃液体油(> 50%)。X射线吸收精细结构,X射线光电子能谱和H 2表征催化剂程序升温还原表明,ReO x / AC的活性可能归因于Re IV-VI的存在。活性炭和氧化oxide的表面氧基团之间的相互作用也可能在C–O键的断裂中起重要作用。值得注意的是,ReO x / AC催化的C–O键裂解途径超出了典型的脱氧脱水机理。更重要的是,2D-HSQC-NMR和GPC表征表明ReO x/ AC不仅在β-O-4裂解中表现出高
On the Mechanism of Ylide-Mediated Cyclopropanations: Evidence for a Proton-Transfer Step and Its Effect on Stereoselectivity
作者:Samantha L. Riches、Chandreyee Saha、Noelia Fontán Filgueira、Emma Grange、Eoghan M. McGarrigle、Varinder K. Aggarwal
DOI:10.1021/ja910631u
日期:2010.6.9
with chiral sulfur ylides. It had previously been found that semi-stabilized sulfoniumylides (e.g., Ph-stabilized) reacted with cyclic and acyclic enones and substituted acrylates with high ee and that stabilized sulfoniumylides (e.g., ester-stabilized) reacted with cyclic enones again with high ee. The current study has focused on the reactions of stabilized sulfoniumylides with acyclic enones
在本文中,我们描述了迈克尔受体与手性硫叶立德环丙烷化的研究。先前已经发现,半稳定的锍叶立德(例如,Ph-稳定的)与环状和非环状烯酮以及取代的丙烯酸酯反应,具有高 ee 并且稳定的锍叶立德(例如,酯稳定的)再次与具有高 ee 的环烯酮反应. 目前的研究集中在稳定的锍叶立德与无环烯酮的反应上,这些反应出乎意料地降低了 ee。此外,在与甲基乙烯基酮 (MVK) 的反应中观察到 ee 与叶立德稳定性的明显相关性:酮稳定的叶立德产生 25% ee,酯稳定的叶立德产生 46% ee,酰胺稳定的叶立德产生 89% ee。据信,甜菜碱形成后,会出现一个不寻常的质子转移步骤,这会损害该过程的对映选择性。因此,在将稳定的叶立德添加到迈克尔受体后,甜菜碱中间体内的快速和可逆的分子内质子转移,在闭环之前,导致 ee 的侵蚀。最稳定的叶立德(酮)发生最大程度的质子转移。当用氘标记的锍叶立德进行相同的反应时,在所有情况下都观察到更高的