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Mónica Álvarez-Pérez, Maria Frutos Pastor, Alma Viso, Roberto Fernández de la Pradilla, Maria C De La Torre, Miguel A Sierra, Heinz Gornitzka, Catherine Hemmert
An unprecedented stereoselective domino reaction of 1,6-enynes with an aryl ring at C3-C4 in the presence of gold(I) catalysts at low temperature is described. This process involves a novel 5-exo-dig cycloisomerization-dimerization sequence to afford formal Diels-Alder adducts that undergo a smooth gold-catalyzed double bond migration at room temperature. In addition, the first examples of the gold mesoionic carbene mediated [2+2+2] cycloaddition of these enynes with benzaldehyde are reported.
June 26, 2017: Journal of Organic Chemistry
Joydev K Laha, Mandeep Kaur Hunjan, Rohan A Bhimpuria, Deepika Kathuria, Prasad V Bharatam
A palladium-catalyzed tandem oxidative annulation of primary benzamides with acrylates via intermolecular N-alkenylation followed by intramolecular C-alkenylation yielded a stereoselective synthesis of (E)-3-methyleneisoindolin-1-ones. The study unveils, for the first time, that only E-enamides could undergo intramolecular oxidative cyclization under the optimized conditions to give isoindolinones. The current strategy represents an umpolung strategy when compared to the literature approaches that use benzamides...
June 26, 2017: Journal of Organic Chemistry
Junjun Feng, Xin Li
A novel bifunctional squaramide-catalyzed vinylogous Michael-Michael cascade reaction of 3-alkylidene oxindoles with nitroolefin enoates was developed. This convenient, one-pot cascade reaction serves as a powerful tool for the enantioselective construction of potential bioactive chiral chromans, which have three continuous tertiary stereocenters, in moderate to good yields (up to 85%) with excellent stereoselectivities (up to >19:1 dr and >99% ee).
June 26, 2017: Journal of Organic Chemistry
Mª Ángeles García, Nuria Menéndez-López, Karina Boltes, María Castro-Puyana, Mª Luisa Marina
A capillary micellar electrokinetic chromatography (MEKC) method was developed enabling the stereoselective separation of the insecticide bioallethrin. The use of sodium deoxycholate bile salt and acetyl-β-cyclodextrin (acetyl-β-CD) made possible the separation of bioallethrin stereoisomers with a high enantioresolution (7.4) in a short analysis time (6.5min). The analytical characteristics of the developed method were evaluated in terms of linearity, accuracy, precision, and limits of detection (LOD) and quantitation (LOQ) showing a good performance for the quantitation of bioallethrin stereoisomers with LODs of 0...
June 19, 2017: Journal of Chromatography. A
Farid W van der Mei, Changming Qin, Ryan J Morrison, Amir H Hoveyda
A practical method for enantioselective synthesis of fluoroalkyl-substituted Z-homoallylic tertiary alcohols has been developed. Reactions may be performed with ketones containing a polylfluoro-, trifluoro-, difluoro-, and monofluoroalkyl group along with an aryl, a heteroaryl, an alkenyl, an alkynyl, or an alkyl substituent. Readily accessible unsaturated organoboron compounds serve as reagents. Transformations were performed with 0.5-2.5 mol % of a boron-based catalyst, generated in situ from a readily accessible valine-derived aminophenol and a Z- or an E-γ-substituted boronic acid pinacol ester...
June 24, 2017: Journal of the American Chemical Society
Magnus Rueping
A manganese catalyzed regio- and stereoselective hydroarylation of allenes is reported. The C-H functionalization protocol offers access to various alkenylated indoles with excellent yields. Moreover, a hydroarylation/cyclization cascade involving an unexpected C-N bond cleavage and aryl shift has been developed which provides a new synthetic approach to substituted pyrroloindolones.
June 24, 2017: Angewandte Chemie
Padam P Acharya, Kedar N Baryal, Cristin E Reno, Jianglong Zhu
Stereoselective synthesis of S-linked trisaccharide glycal of angucycline antitumor antibiotic derhodinosylurdamycin A is described. The synthesis has been accomplished employing our previously reported umpolung S-glycosylation strategy - stereoselective sulfenylation of 2-deoxy glycosyl lithium. It was found that sugar-derived thiocyanate was a better electrophile than corresponding asymmetric disulfide in this type of stereoselective sulfenylation.
June 15, 2017: Carbohydrate Research
Shao-Xia Lin, Gui-Jun Sun, Qiang Kang
We report an efficient enantioselective conjugate addition of photogenerated α-amino radicals to Michael acceptors catalyzed by a newly prepared chiral-at-metal rhodium complex. This protocol shows that a single Rh(iii) complex can serve not only as a Lewis acid but also as a photoredox catalyst to control the stereoselectivity during the bond formation.
June 23, 2017: Chemical Communications: Chem Comm
Misato Teramura, Jiro Harada, Hitoshi Tamiaki
A chlorosome is a large and efficient light-harvesting antenna system found in some photosynthetic bacteria. This system comprises self-aggregates of bacteriochlorophyll (BChl) c, d, or e possessing a chiral 1-hydroxyethyl group at the 3-position, which plays a key role in the formation of the supramolecule. Biosynthesis of chlorosomal pigments involves stereoselective conversion of 3-vinyl group to 3-(1-hydroxyethyl) group facilitated by a 3-vinyl hydratase. This 3-vinyl hydration also occurs in BChl a biosynthesis, followed by oxidation that introduces an acetyl group at the 3-position...
June 22, 2017: Photosynthesis Research
Shu-Mei Yang, Ganapuram Madhusudhan Reddy, Tzu-Ping Wang, Yu-Sheng Yeh, Min Wang, Wenwei Lin
A highly enantioselective cascade reaction for the generation of five quaternary stereocenters in one-pot operation is reported for the first time in the history of organic synthesis. Cinchona-alkaloid derived hydrogen-bonding catalyst furnished structurally complex cascade products from simple substrates in excellent yields and stereoselectivities.
June 23, 2017: Chemical Communications: Chem Comm
Liela Bayeh, Phong Q Le, Uttam K Tambar
The stereoselective oxidation of hydrocarbons is one of the most notable advances in synthetic chemistry over the past fifty years. Inspired by nature, enantioselective dihydroxylations, epoxidations and other oxidations of unsaturated hydrocarbons have been developed. More recently, the catalytic enantioselective allylic carbon-hydrogen oxidation of alkenes has streamlined the production of pharmaceuticals, natural products, fine chemicals and other functional materials. Allylic functionalization provides a direct path to chiral building blocks with a newly formed stereocentre from petrochemical feedstocks while preserving the olefin functionality as a handle for further chemical elaboration...
June 21, 2017: Nature
Shunsuke Kotani, Kosuke Kai, Masaharu Sugiura, Makoto Nakajima
An efficient method for accessing enantiomerically pure stereopentads via a catalytic asymmetric sequential aldol reaction has been developed for the first time. The enantioselective sequential aldol reaction produces a wide range of chiral stereopentad precursors in good yields with excellent enantioselectivities. The key to success is the use of the sequential catalytic system involving a chiral phosphine oxide catalyst and trichlorosilyl triflate.
June 21, 2017: Organic Letters
Ritabrata Datta, Subrata Ghosh
First asymmetric synthesis of the marine natural product (-)-gracilioether F is described from a D-mannitol derived known compound. The key step involves intramolecular 1, 4-conjugate addition of a hydroxymethyl radical generated from Ti (III) mediated ring opening of a terminal epoxy ring tethered to a butenolide to produce stereoselectively a five-membered ring fused bicyclic lactone, the core structure present in gracilioether F.
June 21, 2017: Journal of Organic Chemistry
Satoshi Takano, Takayoshi Tsuzuki, Takashi Murayama, Tomoshi Kameda, Yasuhiro Kumaki, Takashi Sakurai, Hayato Fukuda, Mizuki Watanabe, Mitsuhiro Arisawa, Satoshi Shuto
A series of 8-substituted analogues of cyclic ADP-4-thioribose (cADPtR, 3), which is a stable equivalent of Ca2+-mobilizing second messenger cyclic ADP-ribose (cADPR, 1), were designed as potential pharmacological tools for the studies on cADPR-modulated Ca2+ signaling pathways. These 8-amino analogue (8-NH2-cADPtR, 4), 8-azido analogue (8-N3-cADPtR, 5), and 8-chloro analogue (8-Cl-cADPtR, 6) were efficiently synthesized, where the stereoselective N1-β-thioribosyladenine-ring closure reaction via an α/β-equilibrium of the 1-aminothioribose derivative and construction of the characteristic 18-membered pyrophosphate ring by Ag+-promoted activation of a phenyl phosphorothioate-type substrate were the two key steps...
June 21, 2017: Journal of Medicinal Chemistry
Xi Wang, Armido Studer
The chemistry of hypervalent iodine(III) compounds has gained great interest over the past 30 years. Hypervalent iodine(III) compounds show valuable ionic reactivity due to their high electrophilicity but also express radical reactivity as single electron oxidants for carbon and heteroatom radical generation. Looking at ionic chemistry, these iodine(III) reagents can act as electrophiles to efficiently construct C-CF3, X-CF3 (X = heteroatom), C-Rf (Rf = perfluoroalkyl), X-Rf, C-N3, C-CN, S-CN, and C-X bonds...
June 21, 2017: Accounts of Chemical Research
Shi-Yong Chen, Xiang-Lei Han, Jia-Qiang Wu, Qingjiang Li, Yunyun Chen, Honggen Wang
Heteroarenes are important structural motif in functional molecules. Reported herein is a Mn(I)-catalyzed 1,2-diheteroarylation of allenes via a C-H activation/Smiles rearrangement cascade. The reaction occurred under additive-free or even solvent-free conditions which allowed the creation of two C-C and one C-N bonds in a single operation. A series of structurally diverse bicyclic or tricyclic compounds bearing an exocyclic double bond were constructed in good to excellent efficiency. The decarboxylative ring-opening of the products led to the facile synthesis of vicinal biheteroaryls...
June 20, 2017: Angewandte Chemie
Oleksandr Plashkevych, Ram Shankar Upadhayaya, Jyoti Chattopadhyaya
In light of the impressive gene-silencing properties of carba-LNA modified oligo DNA and RNA, both in antisense RNA and siRNA approaches, which have been confirmed as proof-of-concept for biochemical applications in post-transcriptional gene silencing, we envision the true potential of carba-LNA modifications to be revealed soon. Herein we provide detailed protocols for synthesis of carba-LNA-A, -G, -(5-Me) C, and -T nucleosides on a medium/large scale (gram scale), as well as important guidelines for incorporation of these modified carba-LNAs into DNA or RNA oligonucleotides...
June 19, 2017: Current Protocols in Nucleic Acid Chemistry
Pramod K Sahu, Dnyandev B Jarhad, Gyudong Kim, Lak Shin Jeong
5'-Homo-4'-selenonucleosides, a class of next-generation nucleosides, are synthesized from D-ribose via a 4-selenosugar intermediate. The key step in synthesizing this intermediate is a seleno-Michael reaction. 5'-Homo-4'-selenouridine and -adenosine are prepared using Pummerer-type and Vorbrüggen condensation, respectively. © 2017 by John Wiley & Sons, Inc.
June 19, 2017: Current Protocols in Nucleic Acid Chemistry
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
San-Ni Hong, Yang Liu, Richmond Lee, Zhiyong Jiang
A direct strategy to construct chiral secondary C-O bonds for quaternary carbon stereocenters at the nonadjacent β-position is described. Methylene 1,3-oxazolidine-2,4-diones were for the first time employed in an asymmetric reaction as viable electrophiles undergoing a tandem conjugate addition-protonation process. Using an l-amino acid-based urea-tertiary amine catalyst, the reaction with 3-substituted oxindoles gave valuable protonation adducts featuring 1,3-quaternary-tertiary (C-O) nonadjacent stereocenters in high yields and excellent stereoselectivities...
June 19, 2017: Chemical Communications: Chem Comm
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