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Kei Iio, Shusuke Sachimori, Tomomi Watanabe, Haruhiko Fuwa
Intramolecular double hydroalkoxylation of internal alkynes could be achieved using a Grubbs-type ruthenium carbene complex or its modified species to deliver a series of bridged- and spiroacetal derivatives in moderate to good yields. This study represents a new example of nonmetathetic reactions catalyzed by Grubbs-type ruthenium carbene complexes.
December 5, 2018: Organic Letters
Claudia Schmidt, Lucia Albrecht, Shantheya Balasupramaniam, Rainer Misgeld, Bianka Karge, Mark Brönstrup, Aram Prokop, Knut Baumann, Stephan Reichl, Ingo Ott
Gold complexes with N-heterocyclic carbene (NHC) ligands have been attracting major attention in medicinal inorganic chemistry based on their favorable antiproliferative effects and the structural versatility of the coordinated NHC ligands. Here we present a novel complex of the type (NHC)2Au+, which represents a substantially improved and selective TrxR inhibitor compared to close structural analogues. The complex is highly stable in various solutions over 96 hours, however, comparative cellular uptake studies indicate metabolic transformations inside cells over time...
December 5, 2018: Metallomics: Integrated Biometal Science
Yoko Nakagawa, Naofumi Nakayama, Hitoshi Goto, Ikuhide Fujisawa, Soda Chanthamath, Kazutaka Shibatomi, Seiji Iwasa
Computational chemical analysis of Ru(II)-Pheox-catalyzed highly enantioselective intramolecular cyclopropanation reactions was performed using density functional theory (DFT). In this study, cyclopropane ring-fused γ-lactones, which are 5.8 kcal/mol more stable than the corresponding minor enantiomer, are obtained as the major product. The results of the calculations suggest that the enantioselectivity of the Ru(II)-Pheox-catalyzed intramolecular cyclopropanation reaction is affected by the energy differences between the starting structures 5l and 5i...
December 4, 2018: Chirality
Jiping Hao, Yi Xu, Zhongliang Xu, Zhiqiang Zhang, Weibo Yang
A Pd-catalyzed, highly regioselective and stereoselective three-component domino allylic substitution/N-H carbene insertion reaction under mild conditions is described. This reaction demonstrates a wide substrate scope and satisfactory functional group tolerance, providing a broad range of allylic sulfone-containing amino acid derivatives. Moreover, DBU mediates highly diastereoselective cross-dehydrogenative coupling annulation of allylic sulfones without using peroxides or any metal oxidants. This developed protocol affords 7-membered ring heterocyclic compounds incorporating both sulfone-containing amino acid esters and one quaternary carbon center...
December 4, 2018: Organic Letters
Shin Ando, Ryota Miyata, Hirofumi Matsunaga, Tadao Ishizuka
In addition to phosphanes, olefins, amines, and amides, over the past two decades N-heterocyclic carbene (NHC) has emerged as a useful alternative ligand. Based on a number of derivatization studies on NHC ligands, imidazol-2-ylidene and imidazolin-2-ylidene became the standard heterocyclic form, and bulky substituents have commonly been introduced on the nitrogen(s) adjacent to carbenic carbons. Our group previously developed NHCs equipped with non-carbenic carbons with a bicyclic architecture that gives them unique steric properties that make them bulky but accessible...
December 4, 2018: Journal of Organic Chemistry
Stephanie A Blaszczyk, Timothy C Homan, Weiping Tang
As one of the four fundamental building blocks of life, carbohydrates assume varied and expansive roles in biological contexts. More in-depth understanding of carbohydrates and their interactions, however, is often restricted by our inability to synthesize and subsequently functionalize them in a site-selective manner. This review will summarize recent advances in the site-selective functionalization of carbohydrates using organocatalysts, including achiral catalysts, chiral nucleophilic bases, chiral N-heterocyclic carbenes, and chiral phosphoric acids, with an emphasis on the catalytic nature in each case...
November 23, 2018: Carbohydrate Research
Zeming Huang, Shaowu Wang, Xiancui Zhu, Qingbing Yuan, Yun Wei, Shuangliu Zhou, Xiaolong Mu
Four amidate-functionalized N-heterocyclic carbene (NHC) rare-earth metal amido complexes [(κ2 -N,O-κ1 -L)2 REN(SiMe3 )2 ] (L = 1-(C6 H5 C═ONCH2 CH2 )-3-(CH3 )3 C6 H2 (N(CH)2 NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(C6 H5 C═ONHCH2 CH2 )-3-(CH3 )3 C6 H2 -(N(CH)2 NCH))Br (H2 LBr) with 5 equiv of KN(SiMe3 )3 followed by treatment with 1 equiv of RECl3 in tetrahydrofuran at -40 °C. These complexes were fully characterized, and their catalytic activities toward hydroboration of unactivated imines and nitriles were investigated, and it was found that these complexes displayed excellent activities as well as remarkable functional group compatibility for imine and nitrile substrates such as halo-, alkyl-, hydroxyl-, N, N-dimethylamino-, and nitro- substituents...
December 3, 2018: Inorganic Chemistry
Dongyang Wang, Qi Chen, Xuebing Leng, Liang Deng
Aiming to get knowledge on the reactivity of low-coordinate cobalt(0) species toward primary phosphines, the reactions of [(IPr)Co(vtms)2 ] and [(ICy)2 Co(vtms)] (IPr = 1,3-bis(2',6'-diisopropylphenyl)imidazol-2-ylidene, ICy = 1,3-dicyclohexylimidazol-2-ylidene, and vtms = vinyltrimethylsilane) with several primary aryl phosphines have been examined. The reactions of [(IPr)Co(vtms)2 ] and [(ICy)2 Co(vtms)] with H2 PDmp (Dmp = 2,6-dimesitylphenyl) at 80 °C furnish the diamagnetic cobalt(I) phosphido complexes [(NHC)Co(PHDmp)] (NHC = IPr, 1; ICy, 2) that feature the Co-(η6 -mesityl) interaction...
December 3, 2018: Inorganic Chemistry
Hiroki Haruki, Shigeo Yasuda, Kazunori Nagao, Hirohisa Ohmiya
Dehydrative allylation between widely available aldehydes and allylic alcohols to afford β,γ-unsaturated ketones was enabled by a synergistic merger of a thiazolium N-heterocyclic carbene catalyst and a palladium-bisphosphine catalyst.
November 30, 2018: Chemistry: a European Journal
Yifan Ping, Taiwei Chang, Kang Wang, Jingfeng Huo, Jianbo Wang
A palladium-catalyzed oxidative borylation reaction of conjugated enynones is developed. This reaction represents a new method for the synthesis of furyl-substituted alkenylboronates. The reaction works well with a series of conjugated enynones. Boryl migratory insertion of the palladium carbene intermediate is proposed as the key step in these transformations.
December 3, 2018: Chemical Communications: Chem Comm
Shi-Ya Zhu, Hua Zhang, Qing-Wei Ma, Dou Liu, Xin-Ping Hui
The first activation of saturated acid chlorides by oxidative N-heterocyclic carbene catalysis has been successfully utilized to synthesize enantio-enriched spirooxindole lactones and δ-lactones. The reaction involves the transformation of the β sp3 carbon of saturated acid chlorides into an electrophilic carbon as a key step. The product was obtained in excellent yield and stereoselectivity.
December 3, 2018: Chemical Communications: Chem Comm
Mengru Mira Zhang, Don L Rempel, Michael L Gross
Fast Photochemical Oxidation of Protein (FPOP), based on a pulsed KrF laser (248nm) for free-radical generation, is a biophysical method that utilizes hydroxyl radicals to footprint proteins in solution. FPOP has been recognized for structural proteomics investigations, including epitope mapping, protein-aggregation characterization, protein-folding monitoring, and binding-affinity determination. The distinct merits of the platform are: i) the use of a scavenger to control radical lifetime and allow fast ("snapshot") footprinting of solvent-accessible residues in a protein; ii) the employment of a flow system to enable single-shot irradiation of small plugs of the targeted sample; iii) the use of methionine and catalase after radical oxidation chemistry to prevent post-oxidation with residual oxidizing species; and iv) the utilization of mature mass spectrometry-based proteomic methods to afford detailed analysis...
November 28, 2018: Free Radical Biology & Medicine
Marco V Mijangos, Luis D Miranda
Aspidospermidine, vincadifformine, 1,2-dehydroaspidospermidine, goniomitine, and quebrachamine, five Aspidosperma alkaloids distributed within three structurally diverse topologies, were synthesized from a single molecular scaffold, namely indole-valerolactam 6. This common intermediate can be divergently manipulated, through the incorporation of conformational and electronic constraints that influence the chemo-selectivity of the iminium ion derived therefrom, between three different reaction paths: N(1) vs...
November 30, 2018: Organic & Biomolecular Chemistry
Kun-Quan Chen, Zhong-Hua Gao, Song Ye
The enantioselective N-heterocyclic carbene-catalyzed [3+3] annulation of α-bromoenals via dynamic kinetic resolution (DKR) of enamines and normal resolution of α,α-disubstituted imines were developed. The corresponding substituted dihydropyridones in good yields with excellent diastereo- and enantioselectivities, and high selective factor (up to 83) was realized for the resolution of α,α-disubstituted imines.
November 30, 2018: Angewandte Chemie
Wei Xu, Jidong Zhao, Xiangdong Li, Yuanhong Liu
Benzo[d]isoxazoles are found to act as novel nucleophiles to undergo gold-catalyzed [5+1] or [5+2] cycloaddition reactions with ynamides. The reaction provides a concise and chemoselective access to polysubstituted 2H-benzo[e][1,3]oxazines or benzo[f][1,4]oxazepines. In addition, benzo[d]isoxazoles can also react with gold-carbene intermediates derived from propargyl esters to afford [5+1] annulation products.
November 30, 2018: Journal of Organic Chemistry
Yang Wang, Ling-Bo Qu, Donghui Wei
The novel base-controlled mechanisms for N-heterocyclic carbene (NHC)-catalyzed divergent [3 + 3] and [3 + 2] annulation reactions were examined by using DFT method. The reaction initiates with the complexation of NHC and enal to give the Breslow intermediate, which diverges afterward. Then, the azomethine imine can either react with Breslow intermediate to give six-membered ring product, or the β-carbon protonation happens for forming the enolate intermediate controlled by different bases. The formed enolate intermediate reacts with azomethine imine to afford five-membered ring product...
November 29, 2018: Chemistry, An Asian Journal
Kasper Skov Kjær, Nidhi Kaul, Om Prakash, Pavel Chábera, Nils W Rosemann, Alireza Honarfar, Olga Gordivska, Lisa A Fredin, Karl-Erik Bergquist, Lennart Häggström, Tore Ericsson, Linnea Lindh, Arkady Yartsev, Stenbjörn Styring, Ping Huang, Jens Uhlig, Jesper Bendix, Daniel Strand, Villy Sundström, Petter Persson, Reiner Lomoth, Kenneth Wärnmark
Iron's abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer (CT) states of most Fe complexes are limited by picosecond or sub-picosecond deactivation through low-lying metal centered (MC) states, resulting in inefficient electron transfer reactivity and complete lack of photoluminescence. Here we show that octahedral coordination of Fe(III) by two mono-anionic facial tris -carbene ligands can suppress such deactivation dramatically...
November 29, 2018: Science
Zijun Wu, Jian Wang
An unprecedented example of NHC-catalyzed chemoselective S-O bond cleavage of dinitrobenzenesulfonic carbamates is described. This protocol features several advantages, including mild reaction conditions, broad substrate scope, and operational simplicity, which allows it to be an attractive synthetic method for hydroxylamine synthesis. Notably, dinitrobenzenesulfonic carbamates not only work as "O" synthons but also serve as an efficient oxidant in this reaction.
November 29, 2018: Organic Letters
Ming Li, Jia-Hui Wang, Wei Li, Li-Rong Wen
A mild and straightforward synthetic protocol for the construction of 2-(oxazol-5-yl)phenol derivatives promoted by K2 CO3 from N-phenoxyamides and alkynylbenziodoxolones at room temperature has been developed. Importantly, this protocol involves a tandem sequence that includes [3,3]-rearrangement/alkylidene carbene insertion/Michael addition/cyclization. The metal-free conditions, broad substrate scope, and simple execution make this novel protocol very attractive.
November 29, 2018: Organic Letters
Mathias Schäfer, Albrecht Berkessel, Helmut Schwarz, Mathias Paul, Maria Schlangen, Eric Detmar, Martin Breugst, Jörg-Martin Neudörfl
N-Heterocyclic carbenes (NHCs; :C) can interact with azolium salts (CH+) by either forming an H-bonded aggregate (CHC+), or a covalent C-C bond (CCH+). In this study, intramolecular NHC-azolium salt interactions of aromatic imidazolin-2-ylidenes and saturated imidazolidin-2-ylidenes were investigated in the gas phase by travelling wave ion mobility mass spectrometry (TW IMS) and DFT calculations. The TW IMS experiments provided evidence for the formation of these important intermediates in the gas phase, and they identified the predominant aggregation mode (H-bond vs...
November 29, 2018: Chemistry: a European Journal
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