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Organic Letters

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https://www.readbyqxmd.com/read/28445072/an-approach-to-the-core-of-lactonamycin
#1
Philip J Parsons, Daniel R Jones, Lee J Walsh, Lewis A T Allen, Ada Onwubiko, Lewis Preece, Johnathan Board, Andrew J P White
A cascade reaction has been developed for the synthesis of lactonamycin. In this paper, we demonstrate that a transition-metal-free thermal ene-diyne cyclization can be used for the construction of the entire core of the antibiotic lactonamycin and anticancer agent lactonamycin Z.
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445070/enantioselective-4-2-cycloaddition-of-o-quinone-methides-and-vinyl-sulfides-indirect-access-to-generally-substituted-chiral-chromanes
#2
Zhaobin Wang, Jianwei Sun
A catalytic asymmetric [4 + 2] cycloaddition of ortho-quinone methides (o-QMs) is described. With the readily available vinyl sulfides as the key 2π partner and a properly chosen chiral phosphoric acid catalyst, the reaction proceeded under mild conditions to form the corresponding adduct with high enantio- and diastereoselectivity. Owning to the easy removal and conversion of the sulfenyl group in the product, the present process provides indirect access to generally substituted chromanes previously lacking easy access...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445064/enantioselective-michael-addition-of-photogenerated-o-quinodimethanes-to-enones-catalyzed-by-chiral-amino-acid-esters
#3
Xiaoqian Yuan, Shupeng Dong, Zhen Liu, Guibing Wu, Chuncheng Zou, Jinxing Ye
The first example of a photoexcitated amine-catalyzed process for asymmetric Michael addition of o-quinodimethanes to enones is described. In the presence of simple chiral amino acid esters, a variety of Michael adducts were generally obtained in good yields and excellent stereoselectivities. This strategy can be successfully applied to 3-substituted-2-cyclohexenones and provides an asymmetric access to all-carbon quaternary centers. Furthermore, the high stereocontrol was explained by means of density-functional theory (DFT) calculations...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445063/role-of-configuration-at-c6-in-catalytic-activity-of-l-proline-derived-bifunctional-organocatalysts
#4
Hui Jin, Soo Min Cho, Juyeol Lee, Do Hyun Ryu
l-Proline-derived chiral bifunctional (thio)urea organocatalysts epi-PTU and epi-PU were newly synthesized, and their catalytic performances were compared with their C6 epimeric catalysts PTU and PU in various Michael reactions of nitrostyrene in terms of reactivities and stereoselectivities. The experimental results indicate that a proper relative stereochemistry at C2 and C6 in l-proline-derived bifunctional organocatalysts is important for successful catalysis and that catalysts (PTU and PU) with the 2S,6R configuration are much more efficient...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445062/regioselective-functionalization-of-enamides-at-the-%C3%AE-carbon-via-unsymmetrical-2-amidoallyl-cations
#5
Mirza A Saputra, Nitin S Dange, Alexander H Cleveland, Joshua A Malone, Frank R Fronczek, Rendy Kartika
A new method to functionalize enamides via an intermediacy of unsymmetrical 2-amidoallyl cations is reported. Generated under mild Brønsted acid catalysis, these reactive species were found to undergo addition with various nucleophiles at the less substituted α-carbon to produce highly substituted enamides in high yields with complete control of regioselectivity.
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445061/synergistic-visible-light-photoredox-nickel-catalyzed-synthesis-of-aliphatic-ketones-via-n-c-cleavage-of-imides
#6
Javad Amani, Rauful Alam, Shorouk Badir, Gary A Molander
An electrophilic, imide-based, visible-light-promoted photoredox/Ni-catalyzed cross-coupling reaction for the synthesis of aliphatic ketones has been developed. This protocol proceeds through N-C(O) bond activation, made possible through the lower activation energy for metal insertion into this bond due to delocalization of the lone pair of electrons on the nitrogen by electron-withdrawing groups. The operationally simple and mild cross-coupling reaction is performed at ambient temperature and exhibits tolerance for a variety of functional groups...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445060/asymmetric-synthesis-of-carbocyclic-propellanes
#7
Lisa M Schneider, Volker M Schmiedel, Tommaso Pecchioli, Dieter Lentz, Christian Merten, Mathias Christmann
A modular synthesis of functionalized carbocyclic propellanes was developed. Formation of the first of two quaternary bridgehead centers has been achieved by desymmetrization of prostereogenic ketones by either Hajos-Parrish-Eder-Sauer-Wiechert-type processes or Werner's catalytic asymmetric Wittig reaction. The obtained bicyclic enones were subjected to conjugate additions upon which the remaining ring was formed by olefin metathesis. All bridges are amenable to further derivatization, which renders those compounds useful as central units in fragment-based drug discovery or as ligand scaffolds...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28445059/iron-catalyzed-dehydrogenative-sp-3-sp-2-coupling-via-direct-oxidative-c-h-activation-of-acetonitrile
#8
Huimin Su, Luyao Wang, Honghua Rao, Hao Xu
An iron-catalyzed dehydrogenative sp(3)-sp(2) coupling of acetonitrile and 2-arylimidazo[1,2-a]pyridine has been realized, which can serve as a novel approach toward heteroarylacetonitriles. The merit of this strategy is illustrated by the breadth of functional groups tolerated in the transformation and the fast access to pharmaceuticals (such as zolpidem) directly from the heteroarylacetonitriles.
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28443669/pph3-catalyzed-3-2-spiroannulation-of-1c-3n-bisnucleophiles-derived-from-secondary-%C3%AE-ketoamides-with-%C3%AE-acetoxy-allenoate-a-route-to-functionalized-spiro-n-heterocyclic-derivatives
#9
Jiaojiao Xing, Yu Lei, Yu-Ning Gao, Min Shi
A [3 + 2] annulation of α-substituted secondary β-ketoamides with δ-acetoxy-modified allenoate has been developed in the presence of phosphine catalyst. In this spiroannulation reaction, β-ketoamides were used as the bis-nucleophilic partner while the γ,δ-carbon of 5-acetoxypenta-2,3-dienoate participated as a C2 synthon, affording the desired functionalized five-membered N-heterocyclic derivatives in moderate to excellent yields and diastereoselectivities under mild conditions. Preliminary attempts on the asymmetric variant of this reaction have been also examined, giving the corresponding products with moderate ee values...
April 26, 2017: Organic Letters
https://www.readbyqxmd.com/read/28441026/nam7-hydroxylase-is-responsible-for-the-formation-of-the-naphthalenic-ring-in-the-biosynthesis-of-neoansamycins
#10
Juanli Zhang, Shanren Li, Xingkang Wu, Zhixing Guo, Chunhua Lu, Yuemao Shen
Ten new benzenic ansamycins, 5,10-seco-neoansamycins A-J (1-10), were isolated from the nam7-disrupted mutant strain SR201nam1OEΔnam7. These are the benzenic counterparts of the neoansamycins, which provide direct evidence that the putative hydroxylase Nam7 is involved in the formation of naphthalenic ring in neoansamycin biosynthesis and connect benzenic and naphthalenic ansamycins for the first time.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28441024/stereoselective-synthesis-and-evaluation-of-c6%C3%A2-substituted-5a-carbasugar-analogues-of-sl0101-as-inhibitors-of-rsk1-2
#11
Mingzong Li, Yu Li, Katarzyna A Ludwik, Zachary M Sandusky, Deborah A Lannigan, George A O'Doherty
A convergent synthesis of 5a-carbasugar analogues of the n-Pr-variant of SL0101 is described. The analogues were synthesized in an effort to find compounds with potent in vivo efficacy in the inhibition of p90 ribosomal s6 kinase (RSK1/2). The synthesis derived the desired C-4 L-rhamnose stereochemistry from quinic acid and used a highly selective cuprate addition, NaBH4 reduction, Mitsunobu inversion, and alkene dihydroxylation to install the remaining stereochemistry. A Pd-catalyzed cyclitolization stereoselectively installed the aglycon at the anomeric position...
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440656/heteroannulation-of-3-nitroindoles-and-3-nitrobenzo-b-thiophenes-a-multicomponent-approach-toward-pyrrole-fused-heterocycles
#12
P V Santhini, Sheba Ann Babu, Akhil Krishnan R, E Suresh, Jubi John
A simple, efficient, and general multicomponent reaction involving an enolizable ketone, a primary amine, and an N-protected 3-nitroindole was developed for the synthesis of a range of functionalized pyrrolo[3,2-b]indoles. The methodology was efficaciously utilized for the "pyrroloindoliztion" of natural products, the pyrrolization of 3-nitrobenzo[b]thiophene, and the gram-scale synthesis of pyrroloindole. Furthermore, a "one-pot" approach for accessing indolo[3,2-b]indoles was realized.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440653/hydroxytrifluoromethylation-of-alkenes-using-fluoroform-derived-cucf3
#13
Xinkan Yang, Lisi He, Gavin Chit Tsui
Hydroxytrifluoromethylation of alkenes using the fluoroform (CF3H)-derived [CuCF3] reagent is described. In the presence of additive B2Pin2 and air, this reagent effectively facilitates the addition of hydroxy and trifluoromethyl groups across an alkene double bond, a formal hydroxytrifluoromethylation process. Various β-trifluoromethyl alcohols can be synthesized from simple alkenes where the ultimate CF3 source is the industrial byproduct fluoroform.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440651/iron-catalyzed-acyloxyalkylation-of-styrenes-using-hypervalent-iodine-reagents
#14
Zijia Wang, Motomu Kanai, Yoichiro Kuninobu
Iron-catalyzed acyloxyalkylation of styrene derivatives using hypervalent iodine reagents was achieved. The acyloxyalkylation reaction proceeded using various types of styrenes and hypervalent iodine reagents. The acyloxyalkylated products were obtained in moderate to good yields without loss of the functional groups. The reaction proceeded via the formation of radical species derived from hypervalent iodine reagents by decarboxylation.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440649/asymmetric-synthesis-of-trisubstituted-tetrahydrothiophenes-via-in-situ-generated-chiral-fluoride-catalyzed-cascade-sulfa-michael-aldol-reaction-of-1-4-dithiane-2-5-diol-and-%C3%AE-%C3%AE-unsaturated-ketones
#15
Mengying Duan, Yidong Liu, Jun Ao, Lu Xue, Shilong Luo, Yu Tan, Wenling Qin, Choong Eui Song, Hailong Yan
A chiral fluoride-catalyzed asymmetric cascade sulfa-Michael/aldol condensation reaction of 1,4-dithiane-2,5-diol and a series of α,β-unsaturated ketones is described to access chiral trisubstituted tetrahydrothiophene derivatives. The target products, including the spiro tetrahydrothiophene derivatives bearing a five-, six-, and seven-membered ring, were highly functionalized and showed high ee value. This established protocol realized a highly enantioselective reaction with a catalytic amount of KF and Song's chiral oligoEG via in situ generated chiral fluoride to construct useful heterocyclic skeletons with great complexity...
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440081/hydropyridylation-of-olefins-by-intramolecular-minisci-reaction
#16
Samuele Bordi, Jeremy T Starr
An unprecedented cheap, mild and easy methodology for an intramolecular Minisci reaction based on a hydrogen atom transfer (HAT) initiated hydrofunctionalization of olefins was developed. The method is suitable for the construction of unusual dihydropyrano-pyridine and 1,2,3,4-tetrahydronaphthiridine structures and, unlike most similar reactions, does not require exclusion of air from the reaction medium.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28440074/applications-of-synthetic-organic-tetrasulfides-as-h2s-donors
#17
Matthew M Cerda, Matthew D Hammers, Mary S Earp, Lev N Zakharov, Michael D Pluth
In an effort to expand the availability of simple polysulfides for H2S donation, we report here the synthesis and H2S release profiles of bis(aryl) and bis(alkyl) tetrasulfides. The tetrasulfide donors release H2S in a first-order dependence on reduced glutathione (GSH) and release more H2S than the commonly used trisulfide DATS.
April 25, 2017: Organic Letters
https://www.readbyqxmd.com/read/28437119/synthesis-of-naphthoquinolizinones-through-rh-iii-catalyzed-double-c-sp-2-h-bond-carbenoid-insertion-and-annulation-of-2-aryl-3-cyanopyridines-with-%C3%AE-diazo-carbonyl-compounds
#18
Beibei Zhang, Bin Li, Xinying Zhang, Xuesen Fan
An unprecedented Rh(III)-catalyzed double C(sp(2))-H bond carbenoid insertion and annulation of 2-aryl-3-cyanopyridines with α-diazo carbonyl compounds is presented. Through this cascade reaction, a series of naphthoquinolizinone derivatives with a large π-system were efficiently prepared. The reactions could selectively afford naphthoquinolizinones with either an amine or an amide unit attached on the 11-position depending on the nature of the solvent and the additive used. Compared with literature methods, this is a more efficient, convenient, and atom-economic way to provide polycyclic heteroaromatic compounds through direct π-extension of simple aromatics via inert C-H bond activation and functionalization...
April 24, 2017: Organic Letters
https://www.readbyqxmd.com/read/28437118/blue-light-photocatalytic-glycosylation-without-electrophilic-additives
#19
Peng Wen, David Crich
Photocatalytic formation of glycosidic bonds employing stable and readily accessible O-glycosyl derivatives of 2,2,6,6-tetramethylpiperidin-1-ol is presented that employs an iridium-based photocatalyst and blue LEDs. The reaction proceeds at room temperature and in the absence of additives other than 4 Å molecular sieves. Stereoselectivities are modest but nevertheless dependent on the anomeric configuration of the donor, suggesting a substantial degree of concerted character.
April 24, 2017: Organic Letters
https://www.readbyqxmd.com/read/28437113/development-and-application-of-a-recyclable-high-load-magnetic-co-c-hybrid-romp-derived-benzenesulfonyl-chloride-reagent-and-utility-of-corresponding-analogues
#20
Saqib Faisal, Qin Zang, Pradip K Maity, Agnes Brandhofer, Patrick C Kearney, Oliver Reiser, Robert N Grass, Diana Stoianova, Paul R Hanson
The development and application of high-load, recyclable magnetic Co/C hybrid ROMP-derived benzenesulfonyl chloride and analogues is reported. The regeneration and utility of these reagents in the methylation/alkylation of various carboxylic acids is demonstrated via efficient retrieval of the magnetic reagent with a neodymium magnet. Additional reactions employing the analogue sulfonic acid and in situ generated magnetic benzenesulfonyl azide are also reported.
April 24, 2017: Organic Letters
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