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Journal of Organic Chemistry

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https://www.readbyqxmd.com/read/27813414/switching-selectivity-of-alpha-enolic-dithioesters-one-pot-access-to-functionalized-1-2-and-1-3-dithioles
#1
Suvajit Koley, Tanmoy Chanda, Subhasis Samai, Maya Shankar Singh
An operationally simple cascade protocol has been developed for the construction of 1,2- and 1,3-dithiole derivatives from α-enolic dithioesters. 1,2-Dithioles are achieved by the reaction of dithioesters with elemental sulfur in the presence of InCl3 under solvent-free conditions. 1,3-Dithioles have been constructed via DABCO mediated self-coupling of dithioesters in open air enabling the formation of two new CS bonds and one ring in a single operation in contiguous fashion. The reactions proceeded smoothly affording the desired sulfur-rich heterocycles in good to excellent yields, exhibiting gram-scale ability and broad functional groups tolerance utilizing easy to handle cheap and easily available reagents...
November 4, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27813413/construction-of-9h-pyrrolo-1-2-a-indoles-by-a-copper-catalyzed-friedel-crafts-alkylation-annulation-cascade-reaction
#2
Yongqing Sun, Yu Qiao, Haiying Zhao, Baoguo Li, Shufeng Chen
An efficient and concise Cu(OTf)2-catalyzed Friedel-Crafts alkylation/annulation cascade reaction of substituted indoles with 1,2-dicarbonyl-3-enes has been established. This reaction uses readily available starting materials and is operationally simple, thus representing a practical method for the construction of diverse 9H-pyrrolo[1,2-a]indoles bearing a carbonyl group.
November 4, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27813410/total-synthesis-of-the-proposed-structure-for-aromin-and-its-structural-revision
#3
Shunya Takahashi, Daisuke Satoh, Misato Hayashi, Kohta Takahashi, Kazunori Yamaguchi, Takemichi Nakamura, Hiroyuki Koshino
This paper describes the first total synthesis of the proposed structure for aromin, an annonaceous acetogenin possessing an unusual bis-THF ring system, and its 4S,7R-isomer. The key steps involve an oxidative cyclization of a couple of terminal-diene alcohols and an intermolecular metathesis of an alkenyl tetrahydrofuran with an enone carrying a tetrahydrofuranyl lactone. The spectral data of both samples did not match those of aromin. Re-examination of the NMR data using the CAST/CNMR Structure Elucidator and chemical derivations suggested that the real structure of aromin should be revised to be a tetrahydropyran acetogenin, montanacin D...
November 4, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809543/synthesis-of-molecular-seesaw-balances-and-the-evaluation-of-pyridinium-pi-interactions
#4
Shinji Yamada, Natsuo Yamamoto, Eri Takamori
A series of molecular seesaw balances 1-5 have been developed to measure the relative strength of pyridinium-pi (cation-pi) interactions. The cycloaddition of 1-azaanthracene and o-quinodimethane under microwave irradiation afforded the efficient synthesis of 1 and 5. Introduction of substituents to the pyridine ring of balance 1 was achieved to produce 2-4 in good yields. Anion exchange of 1.MeI afforded 1.MeX with a variety of counteranions (X = Cl, Br, I, BF4, PF6, OAc). These balances adopt two distinct conformers, A and B, which are stabilized by a cation-pi interaction and a pi-pi interaction, respectively...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809531/computational-investigation-of-the-aminolysis-of-raft-macromolecules
#5
Gilles B Desmet, Dagmar R D'hooge, Maarten K Sabbe, Marie-Françoise Reyniers, Guy B Marin
This work presents a detailed computational study and kinetic analysis of the aminolysis of dithioates, dithiobenzoates, trithiocarbonates, xanthates and thiocarbamates, which are frequently used as chain transfer agents for reversible addition-fragmentation chain transfer (RAFT) polymerization. Rate coefficients were obtained from ab initio calculations taking into account a diffusional contribution according to the encounter pair model. A kinetic model was constructed and reveals a reaction mechanism of four elementary steps: i) formation of a zwitterionic intermediate, ii) formation of a complex intermediate in which an assisting amine molecule takes over the proton from the zwitterionic intermediate, iii) breakdown of the complex into a neutral tetrahedral intermediate with release of the assisting amine molecule and iv) amine assisted breakdown of the neutral intermediate to the products...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809529/spin-delocalization-in-a-helical-open-shell-hydrocarbon
#6
Prince Ravat, Peter Ribar, Michel Rickhaus, Daniel Häussinger, Markus Neuburger, Michal Juricek
Neutral open-shell molecules, in which spin density is delocalized through a helical conjugated backbone, hold promise as models for investigating phenomena arising from the interplay of magnetism and chirality. Apart from a handful of examples, however, the chemistry of these compounds remains largely unexplored. Here, we examine the prospect of extending spin-delocalization over a helical backbone in a model compound naphtho[3,2,1-no]tetraphene, the first helically chiral open-shell hydrocarbon, in which one benzene ring is fused to [5]helicene, forming a phenalenyl subunit...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809524/photochemistry-of-1-and-2-methyl-5-aminotetrazoles-structural-effects-on-reaction-pathways
#7
Amin Ismael, Rui Fausto, Maria Lurdes Santos Cristiano
The influence of the position of the methyl substituent in 1- and 2-methyl-substituted 5-aminotetrazoles on the photochemistry of these molecules is evaluated. The two compounds were isolated in an argon matrix (15 K) and the matrix was subjected to in situ narrowband UV excitation at different wavelengths, which induce selectively photochemical transformations of different species (reactants and initially-formed photoproducts). The progress of the reactions was followed by infrared spectroscopy, supported by quantum chemical calculations...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809518/ruthenium-catalyzed-selective-hydroboration-of-nitriles-and-imines
#8
Akash Kaithal, Basujit Chatterjee, Chidambaram Gunanathan
Ruthenium-catalyzed hydroboration of nitriles and imines is attained using pinacolborane with unprecedented catalytic efficiency. Chemoselective hydroboration of nitriles over esters is also demonstrated. A simple [Ru(p-cymene)Cl2]2 complex (1) is used as a catalyst precursor, which upon reaction with pinacolborane in situ generates the monohydrido-bridged complex [{(η(6)-p-cymene)RuCl}2(μ-H-μ-Cl)] 2. Further oxidative addition of pinacolborane to intermediate 2 leading to the formation of mononuclear ruthenium hydride species is suggested...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809516/synthesis-of-hydroxysumanene-and-substituent-effect-of-hydroxy-group-on-bowl-inversion-dynamics-and-electronic-structure
#9
Niti Ngamsomprasert, Gautam Panda, Shuhei Higashibayashi, Hidehiro Sakurai
Hydroxysumanene was synthesized from acylsumanenes by Baeyer-Villiger oxidation. DFT calculation predicted the higher bowl inversion energy and deeper bowl structure of hydroxysumanene than those of pristine sumanene. The bowl inversion energy of hydroxysumanene was experimentally determined by 2D-EXSY NMR measurement as 21.2 kcal/mol. The energy was larger than that of pristine sumanene (20.3 kcal/mol), which agreed with the calculation result. Electrochemical measurement indicated the higher HOMO level of hydroxysumanene than that of sumanene, which confirmed the electron-rich character of the phenolic function in the bowl skeleton...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809510/mechanism-of-nickel-catalyzed-selective-c-n-bond-activation-in-suzuki-miyaura-cross-coupling-of-amides-a-theoretical-investigation
#10
Liu Leo Liu, Peng Chen, Ying Sun, Yile Wu, Su Chen, Jun Zhu, Yufen Zhao
In textbooks, the low reactivity of amides is attributed to the strong resonance stability. However, Garg and co-workers recently reported the Ni-catalyzed activation of robust amide C-N bonds, leading to conversions of amides into esters, ketones, and other amides with high selectivity. Among them, the Ni-catalyzed Suzuki-Miyaura coupling (SMC) of N-benzyl-N-tert-butoxycarbonyl (N-Bn-N-Boc) amides with pinacolatoboronate (PhBpin) was performed in the presence of K3PO4 and water. Water significantly enhanced the reaction...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809508/3-methyleneisoindolin-1-one-assembly-via-base-and-cui-l-proline-catalyzed-domino-reaction-mechanism-of-regioselective-anionic-cyclization
#11
Li Li, Benjamin G Janesko
Anionic cyclization of o-alkynylbenzamides is proposed as a crucial step in many heterocycle syntheses. The cyclization can produce three products: Z-3-methylenisoindolin-1-one (Z-5-exo), E-3-methylenisoindolin-1-one (E-5-exo), and isoquinolinone (6-endo). Under base catalysis, the selectivity is generally poor. However, a copper-involved domino reaction of coupling and cyclization gives surprising selectivity for the thermodynamically disfavored Z-5-exo product (Org. Lett. 2009, 11, 1309-1312). We study the selectivity of anionic cyclization in the presence of K2CO3 and copper-l-proline, using surveys of the experimental literature and density functional theory (DFT) calculations...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27809505/homoserine-as-an-aspartic-acid-precursor-for-synthesis-of-proteoglycan-glycopeptide-containing-aspartic-acid-and-sulfated-glycan-chain
#12
Weizhun Yang, Sherif Ramadan, Bo Yang, Keisuke Yoshida, Xuefei Huang
Among many hurdles in synthesizing proteoglycan glycopeptides, one challenge is the incorporation of aspartic acid in the peptide backbone and acid sensitive O-sulfated glycan chains. To overcome this, a new strategy was developed utilizing homoserine as an aspartic acid precursor. The conversion of homoserine to aspartic acid in the glycopeptide was successfully accomplished by late stage oxidation using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and bis(acetoxy)iodobenzene (BAIB). This is the first time that a glycopeptide containing aspartic acid and O-sulfated glycans was synthesized...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27808513/carbasugar-synthesis-via-vinylogous-ketal-total-syntheses-of-mk7607-mk7607-gabosine-a-epoxydine-b-epoxydine-c-epi-gabosine-e-and-epi-mk7607
#13
Soumik Mondal, Kana M Sureshan
Carbasugars, the carbocyclic analogs of sugars, constitute an important class of natural products with more than 140 members known and have attracted much attention due to their diverse biological activities like anticancer, antibacterial, herbicidal, and various enzyme inhibitory activities. As many carbohydrates are involved in various cellular signaling pathways, there is great interest in synthesis and biological exploration of carbasugars. Herein, we have developed a methodology to install an alpha,beta-unsaturated aldehyde functionality on different inositols and derivatives by vinylogous elimination of the O-protecting group under mildly acidic condition...
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27807971/oxazoline-promoted-rh-catalyzed-c-h-amidation-of-benzene-derivatives-with-sulfonamides-and-trifluoroacetamide-a-comparative-study
#14
Tracy M M Maiden, Stephen Swanson, Panayiotis A Procopiou, Joseph P A Harrity
A Rh-catalyzed ortho-amidation of 2-aryloxazolines offers an efficient and direct route to a range of sulfonamides. The scope of the reaction is very broad with respect to sulfonamide substrate, but the position and electronic nature of the substituents on the aryl moiety of the oxazoline lead to a surprising modulation of reactivity. The reactivity of sulfonamides in comparison to trifluoroacetamide is compared, the latter undergoing Rh-catalyzed amidation more rapidly.
November 3, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27806207/radical-mediated-c-h-functionalization-a-strategy-for-access-to-modified-cyclodextrins
#15
Dimitri Alvarez-Dorta, Elisa I León, Alan R Kennedy, Angeles Martin, Ines Perez-Martin, Ernesto Suárez
A simple and efficient radical C-H functionalization to access modified cyclodextrins (CDs) has been developed. The well-defined conformation of glycosidic and aglyconic bonds in alpha-, beta-, and gamma-CDs favors the intramolecular 1,8-hydrogen atom transfer (HAT) promoted by the 6I-O-yl radical which abstracts regioselectively the hydrogen at C5II of the contiguous pyranose. The C5II-radical evolves by a polar crossover mechanism to a stable 1,3,5-trioxocane ring between two adjacent glucoses or alternatively triggers the inversion of one alpha-D-glucose into a 5-C-acetoxy-beta-L-idose unit possessing a 1C4 conformation...
November 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27806203/stereoselective-synthesis-of-5-epi-alpha-sialosides-related-to-the-pseudaminic-acid-glycosides-reassessment-of-the-stereoselectivity-of-the-5-azido-5-deacetamidosialyl-thioglycosides-and-use-of-triflate-as-nucleophile-in-the-zbiral-deamination-of-sialic-acids
#16
Bibek Dhakal, Szymon Buda, David Crich
With a view to the eventual synthesis of glycosyl donors for the stereocontrolled synthesis of pseudaminic acid glycosides, the stereocontrolled synthesis of a D-glycero-D-gulo sialic acid adamantanylthioglycoside carrying an axial azide at the 5-position is described. The synthesis employs levulinic acid as nucleophile in the oxidative deamination of an N-acetyl neuraminic acid thioglycoside leading to the formation of a 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN) derivative selectively protected as 5-O-levulinate...
November 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27806198/a-chiron-approach-to-diversity-oriented-synthesis-of-aminocyclitols-conduramine-f-4-and-polyhydroxyaminoazepanes-from-a-common-precursor
#17
Vimal Kant Harit, Namakkal Govind Ramesh
The total syntheses of aminocyclitols, (-)-conduramine F-4 and polyhydroxyaminoazepanes have been achieved from a common precursor derived from tri-O-benzyl-D-glucal through a 'Diversity-Oriented' approach. Tri-O-benzyl-D-glucal was converted into a protected 1,6-diol through a sequence of steps that include transformation to 2-tosylamidoglucose derivative, selective deprotection of primary C-6 benzyloxy group, LiAlH4 mediated one-step reduction of acetate groups and reductive ring opening of resulting hemiacetal as the key steps...
November 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27806194/fused-fluoran-leuco-dyes-with-large-color-change-derived-from-two-step-equilibrium-iso-aminobenzopyranoxanthenes
#18
Yoshinao Shirasaki, Yuta Okamoto, Atsuya Muranaka, Shinichiro Kamino, Daisuke Sawada, Daisuke Hashizume, Masanobu Uchiyama
Fluorans are popular leuco dyes that are used in various applications, such as carbonless-copy papers and thermal papers. Here, we describe unique leuco dyes in which two fluoran units are fused into a C2h structure (iso-aminobenzopyranoxanthenes; iso-ABPXs). iso-ABPXs exhibited a large two-step color-change (colorless/pink and pink/blue-green) due to opening-closing of two spirolactone rings. The two-step equilibrium among the colorless, pink and blue-green forms could be well controlled by adjusting acid concentration, solvent and/or temperature...
November 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27805820/palladium-catalyzed-synthesis-of-5-iminopyrrolones-through-isocyanide-double-insertion-reaction-with-terminal-alkynes-and-water
#19
Yan He, Ying-Chun Wang, Kun Hu, Xiao-Ling Xu, Heng-Shan Wang, Ying-Ming Pan
With the combination of Pd(dppf)Cl2 and Cu(OAc)2, a variety of 5-iminopyrrolones were synthesized in moderate to good yields from terminal alkynes, isocyanide and water via isocyanide double insertion and cycloaddition reaction. A plausible reaction mechanism for this process is depicted. Furthermore, selected compounds 3c, 3e and 3h exhibited good activities against HepG2 (human liver cancer), NCI-H460 (human lung cancer) and SK-OV-3 (human ovarian cancer) cell lines with IC50 in the range of 10.63-22.63 micromol L-1...
November 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27805813/computational-and-experimental-studies-of-regioselective-snar-halide-exchange-halex-reactions-of-pentachloropyridine
#20
Robert D J Froese, Gregory T Whiteker, Thomas H Peterson, Daniel J Arriola, James M Renga, Justin W Shearer
The Halex reaction of pentachloropyridine with fluoride ion was studied experimentally and computationally with a modified ab initio G3MP2B3 method. The G3 procedure was altered, as the anionic transition state optimizations failed due to the lack of diffuse functions in the small 6-31G* basis set. Experimental Halex regioselectivities were consistent with kinetic control at the 4-position. The reverse Halex reaction of fluoropyridines with chloride sources was demonstrated using precipitation of LiF in DMSO as a driving force...
November 2, 2016: Journal of Organic Chemistry
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