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https://www.readbyqxmd.com/read/28641007/palladium-catalyzed-sn2-cyclization-of-ambivalent-bromoalkadienyl-malonates-preparation-of-medium-to-large-membered-endocyclic-allenes
#1
Hiroaki Ichio, Hidetoshi Murakami, Yen-Chou Chen, Tamotsu Takahashi, Masamichi Ogasawara
A palladium-catalyzed reaction of preparing various endocyclic allenes was developed. The substrates for the reaction were readily available ω-(pronucleophile-tethered)-3-bromo-1,3-alkadienes, and a palladium-catalyst facilitated their unimolecular SN2'-cyclization in the presence of potassium tert-butoxide to give the corresponding 9- to 16-membered endocyclic allenes in fair yields of up to 67% together with the dimeric 16- to 32-membered endocyclic bis-allenes and other oligomeric/polymeric intermolecular reaction products...
June 22, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28640640/dialkylammonium-tert-butylmethylphosphinites-stable-intermediates-for-the-synthesis-of-p-stereogenic-ligands
#2
Ernest Salomó, Amparo Prades, Antoni Riera, Xavier Verdaguer
The preparation of shelf-stable crystalline salts of tert-butylmethylphosphinous acid borane 1 is described. X-ray analysis of diisopropylammonium tert-butylmethylphosphinite borane 6 revealed the presence of a cyclic hydrogen-bond network in the solid state which accounts for an increased melting point and stability. Dialkylammonium phosphinite boranes are convenient precursors of the chiral tert-butylmethylphosphine fragment. Compound 6 can be used directly in SN2@P reactions with various nucleophiles to yield valuable P-stereogenic intermediates and ligands...
June 22, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28631468/pyrene-tagged-ionic-liquids-separable-organic-catalysts-for-sn2-fluorination
#3
Abu Taher, Kyo Chul Lee, Hye Ji Han, Dong Wook Kim
We prepared pyrene-substituted imidazolium-based ionic liquids (PILs) as organic catalysts for the SN2 fluorination using alkali metal fluoride (MF). In this system, the PIL significantly enhanced the reactivity of MF due to the phase-transfer catalytic effect of the imidazolium moiety as well as the metal cation-π (pyrene) interactions. Furthermore, this homogeneous catalyst PIL was easily separated from the reaction mixture using reduced graphene oxide by π-π stacking with the pyrene of PIL.
June 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/28628742/acceleration-of-semiempirical-qm-mm-methods-through-mpi-hybrid-mpi-openmp-and-scf-accelerator-implementations
#4
Pedro Ojeda-May, Kwangho Nam
The present manuscript describes the strategy and implementation of scalable and efficient semiempirical (SE) QM/MM methods in CHARMM. The serial version of the code was first profiled to identify routines that require parallelization. Afterwards, the code was parallelized and accelerated with three approaches. The first approach was the parallelization of the entire QM/MM routines, including the Fock matrix diagonalization routines, using the CHARMM MPI machinery. In the second approach, two different self-consistent field (SCF) energy convergence accelerators were implemented using density and Fock matrices as targets for their extrapolations in the SCF procedure...
June 19, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28628183/an-unprecedented-stereoselective-base-induced-trimerization-of-an-%C3%AE-bromovinylsulfone
#5
Brendan Fisher, Romain J Lepage, Jonathan M White, Young Ye, Elizabeth H Krenske, Mark A Rizzacasa
A unprecedented base-induced trimerization of bromovinylsulfone 1 afforded the cyclohexene 6 as a single diastereoisomer. Optimization of this reaction gave the adduct 6 in 49% yield. A mechanistic rationale for the trimerization involving consecutive SN2' additions and [3,3]-rearrangements and a final stereoselective intramolecular conjugate addition is proposed and supported by M06-2X density functional theory calculations.
June 19, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28613075/syntheses-of-tetrahydrobenzoazepinoindoles-and-dihydrobenzodiazepinoindoles-via-ring-opening-cyclization-of-activated-aziridines-with-2-2-bromophenyl-1h-indoles
#6
Sajan Pradhan, Chandan Kumar Shahi, Aditya Bhattacharyya, Navya Chauhan, Manas K Ghorai
Two efficient, modular, step- and pot-economic strategies to access various 5,6,7,12-tetrahydrobenzo[2,3]azepino[4,5-b]indoles and 6,7-dihydro-5H-benzo[5,6][1,4]diazepino[1,7-a]indoles are disclosed that advance via SN2-type regioselective ring opening of enantiopure aziridines with 2-(2-bromophenyl)-1H-indoles at their C3 and indolyl N centers, respectively, followed by Cu-mediated C-N cyclization which furnishes the products in excellent yields with outstanding enantiomeric excesses (up to >99%).
June 14, 2017: Organic Letters
https://www.readbyqxmd.com/read/28608622/sn2-reactions-at-tertiary-carbon-centers-in-epoxides
#7
Andreas Gansäuer, Stefan Grimme, Yong-Qiang Zhang, Christina Poppel, Anastasia Panfilova, Fabian Bohle
We describe a novel concept for SN2 reactions at tertiary carbon centers in epoxides without activation of the leaving group. Quantum chemical calculations show why SN2 reactions at tertiary carbon centers are proceeding in these systems. Our reaction allows a flexible synthesis of 1,3-diol building blocks for natural product synthesis with excellent control of relative and absolute configuration.
June 13, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28604855/metal-free-formal-carbon-halogen-bond-insertion-facile-syntheses-of-3-halo-3-3-disubstituted-oxindoles-and-spirooxindole-%C3%AE-butyrolactones
#8
Rong Zhou, Rongfang Liu, Kai Zhang, Ling Han, Honghui Zhang, Wenchao Gao, Ruifeng Li
A novel P(NMe2)3-mediated formal carbon-halogen bond insertion of isatins into allylic and benzylic bromides/chlorides has been realized, leading to a facile synthesis of 3-halo 3,3'-disubstituted oxindoles. This reaction relies on the unique dual nucleophilic-electrophilic reactivity pattern of the Kukhtin-Ramirez adduct via a cascade SN2-SN2 process. It also represents a rare metal-free approach for carbon-halogen bond insertion. Upon treatment with trifluoroacetic acid, spirooxindole-γ-butyrolactones have been efficiently prepared from the corresponding insertion products...
June 22, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28604696/a-front-face-sni-synthase-engineered-from-a-retaining-double-sn2-hydrolase
#9
Javier Iglesias-Fernández, Susan M Hancock, Seung Seo Lee, Maola Khan, Jo Kirkpatrick, Neil J Oldham, Katherine McAuley, Anthony Fordham-Skelton, Carme Rovira, Benjamin G Davis
SNi-like mechanisms, which involve front-face leaving group departure and nucleophile approach, have been observed experimentally and computationally in chemical and enzymatic substitution at α-glycosyl electrophiles. Since SNi-like, SN1 and SN2 substitution pathways can be energetically comparable, engineered switching could be feasible. Here, engineering of Sulfolobus solfataricus β-glycosidase, which originally catalyzed double SN2 substitution, changed its mode to SNi-like. Destruction of the first SN2 nucleophile through E387Y mutation created a β-stereoselective catalyst for glycoside synthesis from activated substrates, despite lacking a nucleophile...
June 12, 2017: Nature Chemical Biology
https://www.readbyqxmd.com/read/28598635/deciphering-front-side-complex-formation-in-sn2-reactions-via-dynamics-mapping
#10
István Szabó, Balázs Olasz, Gábor Czakó
Due to their importance in organic chemistry, the atomistic understanding of bimolecular nucleophilic substitution (SN2) reactions shows exponentially growing interest. In this publication, the effect of front-side complex (FSC) formation is uncovered via quasi-classical trajectory computations combined with a novel analysis method called trajectory orthogonal projection (TOP). For both F(-) + CH3Y [Y = Cl,I] reactions, the lifetime distributions of the F(-)···YCH3 front-side complex revealed weakly trapped nucleophiles (F(-))...
June 14, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28589629/observation-of-various-and-spontaneous-magnetic-skyrmionic-bubbles-at-room-temperature-in-a-frustrated-kagome-magnet-with-uniaxial-magnetic-anisotropy
#11
Zhipeng Hou, Weijun Ren, Bei Ding, Guizhou Xu, Yue Wang, Bing Yang, Qiang Zhang, Ying Zhang, Enke Liu, Feng Xu, Wenhong Wang, Guangheng Wu, Xixiang Zhang, Baogen Shen, Zhidong Zhang
The quest for materials hosting topologically protected skyrmionic spin textures continues to be fueled by the promise of novel devices. Although many materials have demonstrated the existence of such spin textures, major challenges remain to be addressed before devices based on magnetic skyrmions can be realized. For example, being able to create and manipulate skyrmionic spin textures at room temperature is of great importance for further technological applications because they can adapt to various external stimuli acting as information carriers in spintronic devices...
June 7, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28580951/enantioselective-decarboxylative-chlorination-of-%C3%AE-ketocarboxylic-acids
#12
Kazutaka Shibatomi, Kazumasa Kitahara, Nozomi Sasaki, Yohei Kawasaki, Ikuhide Fujisawa, Seiji Iwasa
Stereoselective halogenation is a highly useful organic transformation for multistep syntheses because the resulting chiral organohalides can serve as precursors for various medicinally relevant derivatives. Even though decarboxylative halogenation of aliphatic carboxylic acids is a useful and fundamental synthetic method for the preparation of a variety of organohalides, an enantioselective version of this reaction has not been reported. Here we report a highly enantioselective decarboxylative chlorination of β-ketocarboxylic acids to obtain α-chloroketones under mild organocatalytic conditions...
June 5, 2017: Nature Communications
https://www.readbyqxmd.com/read/28574703/direct-formation-of-carbon-sp-3-heteroatom-bonds-from-rh-iii-to-produce-methyl-iodide-thioethers-and-alkylamines
#13
Tyler E Stevens, Karena A Smoll, Karen I Goldberg
Thermolysis of the Rh(III)-Me complex (DPEphos)RhMeI2 (1) results in reductive elimination of MeI. Mechanistic studies are consistent with SN2 attack by I(-) at the Rh(III)-Me group via two separate competing paths. Addition of sulfur and nitrogen nucleophiles allows effective competition and formation of C(sp(3))-S and C(sp(3))-N coupled products in high yields. C(sp(3))-N bond formation is second-order in amine, consistent with amine substitution of iodide at the metal followed by nucleophilic attack at carbon by a second amine...
June 2, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28567264/multi-electron-reactivity-of-a-cofacial-di-tin-ii-cryptand-partial-reduction-of-sulfur-and-selenium-and-reversible-generation-of-s3%C3%AB
#14
Julia M Stauber, Peter Müller, Yizhe Dai, Gang Wu, Daniel G Nocera, Christopher C Cummins
Cofacial bimetallic tin(ii) ([Sn2(mBDCA-5t)](2-), 1) and lead(ii) ([Pb2(mBDCA-5t)](2-), 2) complexes have been prepared by hexadeprotonation of hexacarboxamide cryptand mBDCA-5t-H6 together with double Sn(ii) or Pb(ii) insertion. Reaction of 1 with elemental sulfur or selenium generates di-tin polychalcogenide complexes containing μ-E and bridging μ-E5 ligands where E = S or Se, and the Sn(ii) centers have both been oxidized to Sn(iv). Solution and solid-state UV-Vis spectra of [(μ-S5)Sn2(μ-S)(mBDCA-5t)](2-) (4) indicate that the complex acts reversibly as a source of S3˙(-) in DMF solution with a Keq = 0...
December 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/28559581/synthesis-and-structure-activity-relationships-of-novel-lincomycin-derivatives-part-4-synthesis-of-novel-lincomycin-analogs-modified-at-the-6-and-7-positions-and-their-potent-antibacterial-activities
#15
Yoshinari Wakiyama, Ko Kumura, Eijiro Umemura, Kazutaka Ueda, Takashi Watanabe, Keiko Yamada, Takafumi Okutomi, Keiichi Ajito
To modify lincomycin (LCM) at the C-6 and the C-7 positions, we firstly prepared various substituted proline intermediates (7, 11-15 and 17). These proline intermediates were coupled with methyl 1-thio-α-lincosamide and tetrakis-O-trimethylsilylation followed by selective deprotection of the TMS group at the 7-position gave a wide variety of key intermediates (23-27, 47 and 50). Then, we synthesized a variety of novel LCM analogs modified at the 7-position in application of the Mitsunobu reaction, an SN2 reaction, and a Pd-catalyzed cross-coupling reaction...
May 31, 2017: Journal of Antibiotics
https://www.readbyqxmd.com/read/28553477/the-influence-of-acceptor-nucleophilicity-on-the-glycosylation-reaction-mechanism
#16
S van der Vorm, T Hansen, H S Overkleeft, G A van der Marel, J D C Codée
A set of model nucleophiles of gradually changing nucleophilicity is used to probe the glycosylation reaction mechanism. Glycosylations of ethanol-based acceptors, bearing varying amounts of fluorine atoms, report on the dependency of the stereochemistry in condensation reactions on the nucleophilicity of the acceptor. Three different glycosylation systems were scrutinized, that differ in the reaction mechanism, that - putatively - prevails during the coupling reaction. It is revealed that the stereoselectivity in glycosylations of benzylidene protected glucose donors are very susceptible to acceptor nucleophilicity whereas condensations of benzylidene mannose and mannuronic acid donors represent more robust glycosylation systems in terms of diastereoselectivity...
March 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28537068/regio-and-diastereoselective-synthesis-of-dihydropyridopyrimidines-via-cascade-reactions-of-2-aminopyridines-with-morita-baylis-hillman-bromides-of-nitroalkenes
#17
Lakshminarayana Satham, Irishi N N Namboothiri
The Morita-Baylis-Hillman (MBH) bromides of nitroalkenes have been employed as bielectrophiles for the first time. The 1,3-bielectrophilic reactivity of the MBH bromides has been demonstrated in the synthesis of 3,4-dihydro-2H-pyrido[1,2-a]pyrimidines. The reaction of MBH bromides with 2-aminopyridines takes place in the absence of any reagent in a cascade SN2'-6-endo-trig fashion and is completely regioselective and highly stereoselective. The products, in their hydrobromide salt form, could be conveniently isolated and purified by crystallization...
June 7, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28528446/microsolvation-effects-on-the-reactivity-of-oxy-nucleophiles-the-case-of-gas-phase-sn2-reactions-of-yo-ch3oh-n-1-2-towards-ch3cl
#18
Liu Yun-Yun, Qiu Fang-Zhou, Zhu Jun, Ren Yi, Lau Kai-Chung
The modified G4(MP2) method was applied to explore microsolvation effects on the reactivity of four solvated normal oxy-nucleophiles YO(-)(CH3OH) n=1,2 (Y = CH3, C2H5, FC2H4, ClC2H4), and five α-oxy-nucleophiles YO(-)(CH3OH) n=1,2 (Y = HO, CH3O, F, Cl, Br), in gas-phase SN2 reactions towards the substrate CH3Cl. Based on a Brønsted-type plot, our calculations reveal that the overall activation barriers of five microsolvated α-oxy-nucleophiles are obviously smaller than the prediction from the correlation line constructed by four normal microsolvated ones to different degrees, and clearly demonstrate the existence of an α-effect in the presence of one or two methanol molecule(s)...
June 2017: Journal of Molecular Modeling
https://www.readbyqxmd.com/read/28527381/enantioselectivity-of-haloalkane-dehalogenase-linb-on-the-degradation-of-1-2-dichloropropane-a-qm-mm-study
#19
Xiaowen Tang, Ruiming Zhang, Yanwei Li, Qingzhu Zhang, Wenxing Wang
The hydrolysis dechlorination mechanism of a chiral organochlorinepollutant, 1,2-dichloropropane (DCP), catalyzed by haloalkane dehalogenase LinB has been investigated by using a combined quantum mechanics/molecular mechanics method. LinB was confirmed to be enantioselective towards the catabolism of the racemic mixture. Based on the SN2 nucleophilic substitution mechanism, the dechlorination process was identified as the rate-determining step in LinB-catalyzed degradation of 1,2-dichloropropane, the Boltzmann-weighted average potential barrier of which is 18...
May 12, 2017: Bioorganic Chemistry
https://www.readbyqxmd.com/read/28508468/photocatalytic-self-doped-sno2-x-nanocrystals-drive-visible-light-responsive-color-switching
#20
Dan Han, Baolai Jiang, Ji Feng, Yadong Yin, Wenshou Wang
Visible-light-responsive reversible color-switching systems are attractive to many applications because visible light has superior penetration and causes far less damage to organic molecules than UV. Herein, we report that self-doping of SnO2-x nanocrystals with Sn(2+) red-shifts their absorption to the visible region and simultaneously produces oxygen vacancies, which can effectively scavenge photogenerated holes and thus enable the color switching of redox dyes using visible light. Wavelength-selective switching can also be achieved by coupling the photocatalytic activity of the SnO2-x NCs with the color-switching kinetics of different redox dyes...
June 26, 2017: Angewandte Chemie
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