| 1. |
- Al-Smadi, Derar, 1983-, et al.
(författare)
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Chemical and Biochemical Approaches for the Synthesis of Substituted Dihydroxybutanones and Di-, and Tri-Hydroxypentanones
- 2019
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:11, s. 6982-6991
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Tidskriftsartikel (refereegranskat)abstract
- Polyhydroxylated compounds are building blocks for the synthesis of carbohydrates and other natural products. Their synthesis is mainly achieved by different synthetic versions of aldol-coupling reactions, catalyzed either by organocatalysts, enzymes or metal-organic catalysts. We have investigated the formation of 1,4-substituted 2,3-dihydroxybutan-1-one derivatives from para- and meta-substituted phenylacetaldehydes by three distinctly different strategies. The first involved a direct aldol reaction with hydroxyacetone, dihydroxyacetone or 2-hydroxyacetophenone, catalyzed by the cinchona derivative cinchonine. The second was reductive cross-coupling with methyl or phenyl glyoxal promoted by SmI2 resulting in either 5-substituted 3,4-dihydroxypentan-2-ones or 1,4 bis-phenyl substituted butanones, respectively. Finally, in the third case, aldolase catalysis was employed for synthesis of the corresponding 1,3,4-trihydroxylated pentan-2-one derivatives. The organocatalytic route with cinchonine generated distereomerically enriched syn products (de = 60−99 %), with moderate enantiomeric excesses (ee = 43−56%), but did not produce aldols with either hydroxyacetone or dihydroxyacetone as donor ketones. The SmI2-promoted reductive cross-coupling generated product mixtures with diastereomeric and enantiomeric ratios close to unity. This route allowed for the production of both 1-methyl- and 1-phenylsubstituted 2,3-dihydroxybutanones, at yields between 40−60%. Finally, the biocatalytic approach resulted in enantiopure syn (3R,4S) 1,3,4-trihydroxypentan-2-ones.
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| 2. |
- Andersson, Hanna, 1979, et al.
(författare)
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Photochemically Induced Aryl Azide Rearrangement: Solution NMR Spectroscopic Identification of the Rearrangement Product
- 2017
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:3, s. 1812-1816
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Tidskriftsartikel (refereegranskat)abstract
- Photolysis of ethyl 3-azido-4,6-difluorobenzoate at room temperature in the presence of oxygen results in the regioselective formation of ethyl 5,7-difluoro-4-azaspiro[2.4]hepta-1,4,6-triene-1-carboxylate, presumably via the corresponding ketenimine intermediate which undergoes a photochemical four-electron electrocyclization followed by a rearrangement. The photorearrangement product was identified by multinuclear solution NMR spectroscopic techniques supported by DFT calculations.
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| 3. |
- Angles d'Ortoli, Thibault, et al.
(författare)
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Structure-Reactivity Relationships of Conformationally Armed Disaccharide Donors and Their Use in the Synthesis of a Hexasaccharide Related to the Capsular Polysaccharide from Streptococcus pneumoniae Type 37
- 2017
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:15, s. 8123-8140
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Tidskriftsartikel (refereegranskat)abstract
- To advance the field of glycobiology, efficient synthesis methods of oligosaccharides and glycoconjugates are a requisite. In glycosylation reactions using superarmed donors, both selectivity and reactivity issues must be considered, and we herein investigate these aspects for differently protected beta-linked 2-O-glycosylated glucosyl donors carrying bulky tert-butyldimethylsilyl groups to different extents. The acceptors in reactions being secondary alcohols presents a challenging situation with respect to steric crowding. Conformational pyranose ring equilibria of the superarmed disaccharide donors with axial-rich substituents contained skew and boat conformations, and three-state models were generally assumed. With NIS/TfOH as the promotor, 2,6-di-tert-butyl-4-methylpyridine as the base, and a dichloromethane/toluene solvent mixture, ethyl 1-thio-beta-d-glucosyl disaccharide donors having 6-O-benzyl group(s) besides tert-butyldimethylsilyl groups were efficiently coupled at -40 degrees C to the hydroxyl group at position 3 of glucopyranosyl acceptors to form beta-(1 -> 2),beta-(1 -> 3)-linked trisaccharides, isolated in excellent 95% yield. The more axial-rich donors in skew and boat conformations are thus preorganized closer to the assumed transition state in these glycosylation reactions. The developed methodology was subsequently applied in the synthesis of a multibranched hexasaccharide related to the capsular polysaccharide from Streptococcus pneumoniae type 37, which consists of a beta-(1 -> 3)-linked backbone and a beta-(1 -> 2)-linked side chain of D-glucosyl residues in disaccharide repeating units.
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| 4. |
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| 5. |
- Ayub, Rabia, et al.
(författare)
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Can Baird's and Clar's Rules Combined Explain Triplet State Energies of Polycyclic Conjugated Hydrocarbons with Fused 4nπ- and (4n + 2)π-Rings?
- 2017
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society. - 0022-3263 .- 1520-6904. ; 82:12, s. 6327-6340
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Tidskriftsartikel (refereegranskat)abstract
- Compounds that can be labeled as "aromatic chameleons" are π-conjugated compounds that are able to adjust their π-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T1) of the compounds. Decreases in T1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or trans-bent connectivities. The T1 energies decreased down to those of the parent (isolated) 4nπ-electron units. Simultaneously, we observe an increased influence of triplet state aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of triplet state aromaticity in the central 4nπ-electron units, the most stabilized compounds retain the triplet excitation in Baird π-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar π-sextet character. Interestingly, the T1 energies go down as the total number of aromatic cycles within a molecule in the T1 state increases.
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| 6. |
- Bornhof, Anna-Bea, et al.
(författare)
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Rational Synthesis of 2-Bromoporphyrins and 2,12-Dibromoporphyrins
- 2017
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:23, s. 12908-12913
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Tidskriftsartikel (refereegranskat)abstract
- Bromoporphyrins were prepared by the metal-mediated self-condensation of brominated 1-formyldipyrromethanes. Depending on the conditions, Mg(II)-2,12-dibromoporphyrin and Mg(II)-2-bromoporphyrin could be obtained in up to 11% and 17% isolated yield, respectively. Zn(II) was also a viable templating metal. The positions of the bromine substituents were confirmed by 2D-NMR spectroscopic analysis and the X-ray crystal structure of a derivative. Suzuki and Sonogashira reactions of the bromoporphyrins yielded 2-substituted or 2,12-disubstituted porphyrins with red-shifted absorption and emission spectra. This method provides access to the minimalist core of beta-mono- and beta,beta'-disubstituted porphyrins from readily available starting materials.
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| 7. |
- Brea, Oriana, et al.
(författare)
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Modeling Decomposition of N-Nitrosoamides in a Self-Assembled Capsule
- 2019
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:11, s. 7354-7361
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations are employed to investigate the mechanism and energies of the decomposition of N-nitrosoamides in the presence of a resorcinarene-based self-assembled nanocapsule. From experiments, it is known that confinement in the capsule inhibits the thermal decomposition of these compounds. N-Nitrosoamides with both aromatic and aliphatic substituents are considered here and the calculations show that, for both kinds, binding to the capsule leads to a significant increase in the energy barrier of the rate-determining step, the 1,3 N -> O acyl transfer reaction. A distortion-interaction analysis is conducted to probe the reasons behind the inhibition of the reaction. In addition, we characterized hypothetical intermediates that might be involved in the formation of the decomposition products inside the capsule. Interestingly, it is found that the capsule stabilizes ion-pair species that are unstable in mesitylene solution. Finally, a possible explanation is proposed for the observed encapsulation of the decomposition product of only one of the substrates.
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| 8. |
- Bunrit, Anon, et al.
(författare)
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A General Route to beta-Substituted Pyrroles by Transition-Metal Catalysis
- 2016
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:4, s. 1450-1460
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Tidskriftsartikel (refereegranskat)abstract
- An atom-efficient route to pyrroles substituted in the beta-position has been achieved in four high yielding steps by a combination of Pd, Ru, and Fe catalysis with only water and ethene as side-products. The reaction is general and gives pyrroles substituted in the beta-position with linear and branched alkyl, benzyl, or aryl groups in overall good yields. The synthetic route includes a Pd-catalyzed monoallylation step of amines with substituted allylic alcohols that proceeds to yield the monoallylated products in moderate to excellent yields. In a second step, unsymmetrical diallylated aromatic amines are generated from the reaction of a second allylic alcohol with high selectivity in moderate to good yields by control of the reaction temperature. Ru-catalyzed ring-closing metathesis performed on the diallylated aromatic amines yields the pyrrolines substituted in the beta-position in excellent yields. By addition of ferric chloride to the reaction mixture, a selective aromatization to yield the corresponding pyrroles substituted in the beta-position was achieved. A reaction mechanism involving a palladium hydride, generated from insertion of palladium to O-H of an allyl alcohol, that is responsible for the C-O bond cleavage to generate the pi-allyl intermediate is proposed.
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| 9. |
- Chinthakindi, PK, et al.
(författare)
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On-Water Synthesis of Biaryl Sulfonyl Fluorides
- 2016
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Ingår i: The Journal of organic chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 81:6, s. 2618-2623
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Chow, Shiao, et al.
(författare)
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Sulfonyl Azides as Precursors in Ligand-free Palladium-Catalyzed Synthesis of Sulfonyl Carbamates and Sulfonyl Ureas and Synthesis of Sulfonamides
- 2016
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:7, s. 2681-2691
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Tidskriftsartikel (refereegranskat)abstract
- An efficient synthesis of sulfonyl carbamates and sulfonyl ureas from sulfonyl azides employing a palladium-catalyzed carbonylation protocol has been developed. Using a two-chamber system, sulfonyl azides, PdCl2, and CO gas, released ex situ from Mo(CO)(6), were assembled to generate sulfonyl isocyanates in situ, and alcohols and aryl amines were exploited as nucleophiles to afford a broad range of sulfonyl carbamates and sulfonyl ureas. A protocol for the direct formation of substituted sulfonamides from sulfonyl azides and amines via nucleophilic substitution was also developed.
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| 11. |
- Chow, Shiao Y., et al.
(författare)
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Synthesis of N-Sulfonyl Amidines and Acyl Sulfonyl Ureas from Sulfonyl Azides, Carbon Monoxide, and Amides
- 2017
-
Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 82:5, s. 2515-2522
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Tidskriftsartikel (refereegranskat)abstract
- A Pd-catalyzed and ligand-free carbonylation/cycloaddition/decarboxylation cascade synthesis of sulfonyl amidines from sulfonyl azides and substituted amides at low CO pressure is reported. The reaction proceeds via an initial Pd-catalyzed carbonylative generation of sulfonyl isocyanates from sulfonyl azides, followed by a [2 + 2] cycloaddition with amides and subsequent decarboxylation, which liberates the desired sulfonyl amidines, generating N-2 and CO2 as the only reaction byproducts. Using this simple protocol, a diverse range of sulfonyl amidines was obtained in moderate to excellent yields. In addition, the reaction can also be directed through a more conventional amidocarbonylation pathway by employing N-monosubstituted amide nucleophiles to afford acyl sulfonyl ureas in good yields.
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| 12. |
- Dawaigher, Sami, et al.
(författare)
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A Protocol for the exo-Mono and exo,exo-Bis Functionalization of the Diazocine Ring of Tröger's Base.
- 2015
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 80:24, s. 12006-12014
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Tidskriftsartikel (refereegranskat)abstract
- An efficient protocol has been developed for the exo-mono and exo,exo-bis functionalization of Tröger's base in the benzylic 6 and 12 positions of the diazocine ring. The lithiation of Tröger's base using s-BuLi/TMEDA followed by electrophilic quench affords exo-mono- and exo,exo-bis-substituted derivatives of Tröger's base in good to excellent yields. The variation of the number of equivalents of s-BuLi/TMEDA and the order of addition of the electrophile strongly govern the outcome of the reaction for each electrophile.
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| 13. |
- Deng, Hong-Ping, et al.
(författare)
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Direct Allylation of Quinones with Allylboronates
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:6, s. 3343-3348
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Tidskriftsartikel (refereegranskat)abstract
- Allylboronates undergo C-H allylation of unsubstituted or monosubstituted benzoquinone and naphthoquinone substrates. In the case of 2,5- or 2,6-disubstituted quinones addition involving the substituted carbon takes place. Allylation with stereodefined allylboronates occurs with retention of the configuration.
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| 14. |
- Devaraj, Karthik, et al.
(författare)
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Arynes and Their Precursors from Arylboronic Acids via Catalytic C-H Silylation
- 2019
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Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 84:9, s. 5863-5871
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Tidskriftsartikel (refereegranskat)abstract
- A new, operationally simple approach is presented to access arynes and their fluoride-activated precursors based on Ru-catalyzed C-H silylation of arylboronates. Chromatographic purification may be deferred until after aryne capture, rendering the arylboronates de facto precursors. Access to various new arynes and their derivatives is demonstrated, including, for the first time, those based on a 2,3-carbazolyne and 2,3-fluorenyne core, which pave the way for novel derivatizations of motifs relevant to materials chemistry.
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| 15. |
- Freeman, N.S., et al.
(författare)
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Chromophoric Nucleoside Analogues: Synthesis and Characterization of 6-Aminouracil-Based Nucleodyes
- 2016
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:11, s. 4530-4539
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Tidskriftsartikel (refereegranskat)abstract
- Nucleodyes, visibly colored chromophoric nucleoside analogues, are reported. Design criteria are outlined and the syntheses of cytidine and uridine azo dye analogues derived from 6-aminouracil are described. Structural analysis shows that the nucleodyes are sound structural analogues of their native nucleoside counterparts, and photophysical studies demonstrate that the nucleodyes are sensitive to microenvironmental changes. Quantum chemical calculations are presented as a valuable complementary tool for the design of strongly absorbing nucleodyes, which overlap with the emission of known fluorophores. Förster critical distance (R0) calculations determine that the nucleodyes make good FRET pairs with both 2-aminopurine (2AP) and pyrrolocytosine (PyC). Additionally, unique tautomerization features exhibited by 5-(4-nitrophenylazo)-6-oxocytidine (8) are visualized by an extraordinary crystal structure.
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| 16. |
- Gigant, Nicolas, et al.
(författare)
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Preparation of Tetrasubstituted Olefins Using Mono or Double Aerobic Direct C-H Functionalization Strategies : Importance of Steric Effects
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:5, s. 2796-2803
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Tidskriftsartikel (refereegranskat)abstract
- A novel protocol for the synthesis of tetrasubstituted olefins through a biomimetic approach has been explored. Both mono- and diarylations were performed under ambient oxygen pressure, giving a range of highly hindered tetrasubstituted alkenes. For diarylation of disubstituted substrates, it was demonstrated that the second arylation is the rate-limiting step of the overall transformation.
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| 17. |
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| 18. |
- Hoang, Anita, et al.
(författare)
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An Efficient Synthesis of (±)-Dehaloperophoramidine
- 2017
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:4, s. 2171-2176
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Tidskriftsartikel (refereegranskat)abstract
- Perophoramidine and communesin F are structurally related indole alkaloids with an intriguing polycyclic core containing vicinal all-carbon quaternary stereocenters. Dehaloperophoramidine is a dehalogenated synthetic analogue of perophoramidine. Synthetic studies toward the total synthesis of dehaloperophoramidine have led to the discovery of two novel domino processes, the first encompassing four steps and resulting in the formation of an ortho-amide. A thorough study of the reactivity of the ortho-amide functionality revealed the second domino reaction and ultimately yielded the target molecule. The vicinal all-carbon quaternary stereocenters having trans relative stereochemistry are constructed early in the reaction sequence by employing Overman's samarium mediated reductive dialkylation procedure. Described are the synthetic studies that led to the final eight-step synthesis of dehaloperophoramidine.
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| 19. |
- Hu, Lei, et al.
(författare)
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Chirality Control in Enzyme-Catalyzed Dynamic Kinetic Resolution of 1,3-Oxathiolanes
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:16, s. 8478-8481
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Tidskriftsartikel (refereegranskat)abstract
- The origin of enantioenrichment in enzyme-catalyzed dynamic kinetic resolution of 1,3-oxathiolane derivatives, key intermediates for asymmetric lamivudine synthesis, was elucidated. The chirality control could be determined by chiral HPLC and NOE NMR spectroscopy using a modified 1,3-oxathiolane compound obtained through enzyme-catalyzed selective hydrolysis. Solvent-dependent stereoselectivity was observed under biphasic conditions using different organic solvents with phosphate buffer.
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| 20. |
- Kerdphon, Sutthichat, et al.
(författare)
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C-N Coupling of Amides with Alcohols Catalyzed by N-Heterocyclic Carbene-Phosphine Iridium Complexes
- 2015
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:22, s. 11529-11537
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Tidskriftsartikel (refereegranskat)abstract
- N-heterocyclic carbene-phosphine iridium complexes (NHC-Ir) were developed/found to be a highly reactive catalyst for N-monoalkylation of amides with alcohols via hydrogen transfer. The reaction produced the desired product in high isolated yields using a wide range of substrates with low catalyst loading and short reaction times.
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| 21. |
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| 22. |
- Lee, J. M., et al.
(författare)
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Stereoselectivity in (Acyloxy)borane-Catalyzed Mukaiyama Aldol Reactions
- 2016
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:13, s. 5314-5321
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Tidskriftsartikel (refereegranskat)abstract
- The origin of diastereo- and enantioselectivity in a Lewis acid catalyzed Mukaiyama aldol reaction is investigated using a combination of dispersion corrected DFT calculations and transition state force fields (TSFF) developed using the quantum guided molecular mechanics (Q2MM) method. The reaction proceeds via a closed transition structure involving a nontraditional hydrogen bond that is 3.3 kJ/mol lower in energy than the corresponding open transition structure. The correct prediction of the diastereoselectivity of a Mukaiyama aldol reaction catalyzed by the conformationally flexible Yamamoto chiral (acyloxy) borane (CAB) requires extensive conformational sampling at the transition structure, which is achieved using a Q2MM-derived TSFF, followed by DFT calculations of the low energy conformational clusters. Finally, a conceptual model for the rationalization of the observed diastereo-and enantioselectivity of the reaction using a closed transition state model is proposed.
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| 23. |
- Lindstedt, Erik, et al.
(författare)
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One-Pot Synthesis of Unsymmetric Diaryliodonium Salts from Iodine and Arenes
- 2017
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:22, s. 11909-11914
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Tidskriftsartikel (refereegranskat)abstract
- The first synthesis of unsymmetric diaryliodonium salts directly from iodine and arenes is presented. The methodology provides diaryliodonium salts with the trimethoxyphenyl (TMP) moiety as dummy group. The protocol avoids the customary use of iodoarenes, which can be both expensive and toxic. Excess reagents are not required, and the reactions are performed under mild conditions. O-Arylations with these TMP salts were demonstrated to be highly chemoselective.
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| 24. |
- Liu, Jian Quan, et al.
(författare)
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Silver-Mediated Synthesis of Substituted Benzofuran- and Indole-Pyrroles via Sequential Reaction of ortho-Alkynylaromatics with Methylene Isocyanides
- 2019
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:14, s. 8998-9006
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Tidskriftsartikel (refereegranskat)abstract
- A silver-mediated reaction between 2-ethynyl-3-(1-hydroxyprop-2-yn-1-yl)phenols or 2-ethyn-yl-3-(1-hydroxy-prop-2-yn-1-yl)anilines and methylene isocyanides has been developed. A sequential 5-endo-dig cyclization and [3 + 2] cycloaddition process is proposed. This synthetic strategy is atom- and step-efficient and applicable to a broad scope of substrates, allowing the synthesis of valuable substituted benzofuran- and indole-pyrroles in moderate to high yields.
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| 25. |
- Manojveer, Seetharaman, et al.
(författare)
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Ru-Catalyzed Cross-Dehydrogenative Coupling between Primary Alcohols to Guerbet Alcohol Derivatives : With Relevance for Fragrance Synthesis
- 2018
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 83:18, s. 10864-10870
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Tidskriftsartikel (refereegranskat)abstract
- A simple method has been developed for the cross dehydrogenative coupling between two different primary alcohols using readily available RuCl2(PPh3)3 as a precatalyst through the borrowing-hydrogen approach. The present methodology is applicable to a large variety of alcohol derivatives including long chain aliphatic alcohols and heteroaryl alcohols. In addition, the methodology was applied in a straightforward protocol to synthesize commercially available fragrances such as Rosaphen and Cyclamenaldehyde in good yields.
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| 26. |
- Margalef, Jessica, et al.
(författare)
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High-Atom Economic Approach To Prepare Chiral alpha-Sulfenylated Ketones
- 2019
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:17, s. 11219-11227
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Tidskriftsartikel (refereegranskat)abstract
- Chiral alpha-sulfenylated ketones are versatile building blocks, although there are still several limitations with their preparation. Here we report a new two-step procedure, consisting of Pd-catalyzed hydrothiolation of propargylic alcohols followed by an enantioselective Rh isomerization of allylic alcohols. The isomerization reaction is the key step for obtaining the ketones in their enantioenriched form. The new methodology has a high atom economy and induces good to high levels of enantioselectivity; no waste is produced. A mechanism involving a Rh-hydride-enone intermediate is proposed for the isomerization reaction.
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| 27. |
- Massaro, Luca, et al.
(författare)
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Stereodivergent Synthesis of Trisubstituted Enamides : Direct Access to Both Pure Geometrical Isomers
- 2019
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:21, s. 13540-13548
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Tidskriftsartikel (refereegranskat)abstract
- A stereodivergent strategy has been developed to access either (E)- or (Z)-isomers of trisubstituted enamides. Starting from an extensive range of ketones, it was possible to synthesize and isolate the desired pure isomer by switching the reaction conditions. Lewis acid activation enables the formation of the (E)-isomers in high stereoselectivity (>90:10) and good yields. On the other hand, the use of a Bronsted acid allows the preparation of the (Z)-isomers, again in high selectivity (up to 99:1), with moderate yields.
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| 28. |
- Messersmith, Reid E., et al.
(författare)
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Benzo[b]thiophene Fusion Enhances Local Borepin Aromaticity in Polycyclic Heteroaromatic Compounds
- 2017
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:24, s. 13440-13448
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Tidskriftsartikel (refereegranskat)abstract
- This report documents the synthesis, characterization, and computational evaluation of two isomeric borepin-containing polycyclic aromatics. The syntheses of these two isomers involved symmetrical disubstituted alkynes that were reduced to Z-olefins followed by borepin formation either through an isolable stannocycle intermediate or directly from the alkene via the trapping of a transient dilithio intermediate. Comparisons of their magnetic, crystallographic, and computational characterization to literature compounds gave valuable insights about the aromaticity of these symmetrically fused [b,f]borepins. The fusion of benzo[b]thiophene units to the central borepin cores forced a high degree of local aromaticity within the borepin moieties relative to other known borepin-based polycyclic aromatics. Each isomer had unique electronic responses in the presence of fluoride anions. The experimental data demonstrate that the local borepin rings in these two compounds have a relatively high amount of aromatic character. Results from quantum chemical calculations provide a more comprehensive understanding of local and global aromatic characters of various rings in fused ring systems built upon boron heterocycles.
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| 29. |
- Moriou, Celine, et al.
(författare)
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A Minute Amount of S-Puckered Sugars Is Sufficient for (6-4) Photoproduct Formation at the Dinucleotide Level
- 2015
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:1, s. 615-619
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Tidskriftsartikel (refereegranskat)abstract
- The di-2'-alpha-fluoro analogue of thymidylyl(3',5')thymidine, synthesized to probe the effect of a minimum amount of S conformer on the photoreactivity of dinucleotides, is endowed with only 3% and 8% of S sugar conformation at its 5'- and 3'-end, respectively. This analogue gives rise to the (6-4) photoproduct as efficiently as the dithymine dinucleotide (74% and 66% at the 5'- and 3'-end, respectively) under 254 nm. Our results suggest that the 5'-N, 3'-S conformer gives rise to the (6-4) photoproduct.
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| 30. |
- Moriou, Céline, et al.
(författare)
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C2 '-F Stereoconfiguration As a Puckering Switch for Base Stacking at the Dinucleotide Level
- 2018
-
Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 83:4, s. 2473-2478
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Tidskriftsartikel (refereegranskat)abstract
- Fluorine configuration at C2′ of the bis(2′-fluorothymidine) dinucleotide is demonstrated to drive intramolecular base stacking. 2′-β F-Configuration drastically reduces stacking compared to the 2′-α series. Hence, base stacking emerges as being tunable by the C2′-F stereoconfiguration through dramatic puckering variations scrutinized by NMR and natural bond orbital analysis. Accordingly, 2′-β F-isomer photoreactivity is significantly reduced compared to that of the 2′-α F-isomer.
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| 31. |
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| 32. |
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| 33. |
- Obermeier, Martin, et al.
(författare)
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Phospholones from Diacetylenic Ketones : Synthesis, Properties, and Reactivity
- 2019
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:6, s. 3491-3499
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity of phosphanyl phosphonates toward diacetylenic ketones was studied. Reactions resulted in the selective formation of phospholones via phosphaalkene intermediates. Phospholones were obtained in yields of 37-96% depending on the substituent on the acetylenic unit. Reduction of the phenyl-substituted phospholone resulted in the formation of a persubstituted phosphole bearing a hydroxyl group in position 3 in 64% yield, and its oxidation led to oxaphospholone in 77% yield. Both of these modifications led to substantial changes in the optoelectronic properties of the compounds and bathochromic shifts of the longest wavelength absorption maximum.
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| 34. |
- Osmialowski, Borys, et al.
(författare)
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Influence of Substituent and Benzoannulation on Photophysical Properties of 1-Benzoylmethyleneisoquinoline Difluoroborates
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:4, s. 2072-2080
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Tidskriftsartikel (refereegranskat)abstract
- A series of 1-benzoylmethyleneisoquinoline difluoroborates were synthesized, and their photophysical properties were determined. The effect of the substituent and benzoannulation on their properties was investigated to make a comparison with recently published results focused on related quinolines. The photophysical properties of isoquinoline derivatives differ from those of quinolines, and the most pronounced differences are found for the fluorescence quantum yields. Both experimental and theoretical approaches were used to explain the observed photophysical properties.
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| 35. |
- Poon, Jia-fei, et al.
(författare)
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Regenerable Radical-Trapping Tellurobistocopherol Antioxidants
- 2016
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:24, s. 12540-12544
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Tidskriftsartikel (refereegranskat)abstract
- Tellurobistocopherols 9–11 were prepared by lithiation of the corresponding bromotocopherols, reaction with tellurium tetrachloride and reductive workup. Compounds 9–11 quenched linoleic-acid-derived peroxyl radicals much more efficiently than α-tocopherol in a chlorobenzene/water two-phase system. N-Acetylcysteine or tris(2-carboxylethyl)phosphine as co-antioxidants in the aqueous phase could regenerate the tellurobistocopherols and increase their inhibition times. Antioxidant 11 inhibited peroxidation for 7-fold longer than that recorded with α-tocopherol. Thiol consumption in the aqueous phase was monitored and found to be inversely related to the inhibition time.
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| 36. |
- Popov, Kirill, et al.
(författare)
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Synthesis of Imidates : TFA-Mediated Regioselective Amide Alkylation Using Meerwein's Reagent
- 2016
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:8, s. 3470-3472
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Tidskriftsartikel (refereegranskat)abstract
- Regioselective O-alkylation of an amide to form the corresponding imidate is a common synthetic problem, often resulting in varying amounts of N-alkylation. Screening existing methods for converting amides to imidates gave inconsistent or irreproducible results, sometimes affording N-alkylamide as the major product. A simple and reliable protocol for amide O-alkylation with complete regioselectivity has been designed, and its scope and efficiency demonstrated on a number of substrates.
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| 37. |
- Rukkijakan, Thanya, et al.
(författare)
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Pd-Catalyzed Substitution of the OH Group of Nonderivatized Allylic Alcohols by Phenols
- 2018
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 83:7, s. 4099-4104
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Tidskriftsartikel (refereegranskat)abstract
- Nonactivated phenols have been employed as nucleophiles in the allylation of nonderivatized allylic alcohols to generate allylated phenolic ethers with water as the only byproduct. A Pd[BiPhePhos] catalyst was found to be reactive to give the O-allylated phenols in good to excellent yields in the presence of molecular sieves. The reactions are chemo-selective in which the kinetically favored O-allylated products are formed exclusively over the thermodynamically favored C-allylated products.
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| 38. |
- Runarsson, Ögmundur, et al.
(författare)
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Resolution and Determination of the Absolute Configuration of a Twisted Bis-Lactam Analogue of Tröger's Base: A Comparative Spectroscopic and Computational Study.
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 1520-6904 .- 0022-3263. ; 80:16, s. 8142-8149
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Tidskriftsartikel (refereegranskat)abstract
- The first reported twisted bis-lactam, a racemic Tröger's base (TB) analogue (2), was resolved into its enantiomers on a chiral stationary phase HPLC column. The absolute configuration of (+)-2 was determined to be (R,R)-2 by comparing experimental and calculated vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra. The absolute configuration of (-)-2 was determined by comparing experimental and calculated electronic circular dichroism (ECD) spectra. The corresponding theoretical spectra were calculated using the lowest energy conformation of (R,R)-2 and (S,S)-2 at the B3LYP/6-31G(d,p) level of theory. The absolute configuration of (+)-2 was also determined to (R,R)-2 by anomalous X-ray diffraction (AXRD) in a chiral space group P212121 using Cu-irradiation resulting in a very low Flack parameter of -0.06(3), despite the heaviest element being an oxygen atom, thus unambiguously confirming the results from the spectroscopic studies. We conclude that, for the Tröger's base (TB) analogue (2), we may rank the reliability of the individual methods for AC determination as AXRD ≫ VCD > ECD, while the synergy of all three methods provides very strong confidence in the assigned ACs of (+)-(R,R)-2 and (-)-(S,S)-2.
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| 39. |
- Santoro, Stefano, et al.
(författare)
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Theoretical Study of Mechanism and Stereoselectivity of Catalytic Kinugasa Reaction
- 2015
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 80:5, s. 2649-2660
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the catalytic Kinugasa reaction is investigated by means of density functional theory calculations. Different possible mechanistic scenarios are presented using phenanthroline as a ligand, and it is shown that the most reasonable one in terms of energy barriers involves two copper ions. The reaction starts with the formation of a dicopper-acetylide that undergoes a stepwise cycloaddition with the nitrone, generating a five-membered ring intermediate. Protonation of the nitrogen of the metalated isoxazoline intermediate results in ring opening and the formation of a ketene intermediate. This then undergoes a copper-catalyzed cyclization by an intramolecular nucleophilic attack of the nitrogen on the ketene, affording a cyclic copper enolate. Catalyst release and tautomerization gives the final beta-lactamic product. A comprehensive study of the enantioselective reaction was also performed with a chiral bis(azaferrocene) ligand. In this case, two different reaction mechanisms, involving either the scenario with the two copper ions or a direct cycloaddition of the parent alkyne using one copper ion, were found to have quite similar barriers. Both mechanisms reproduced the experimental enantioselectivity, and the current calculations can therefore not distinguish between the two possibilities.
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| 40. |
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| 41. |
- Sau, Abhijit, et al.
(författare)
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Substrate-Controlled Direct α-Stereoselective Synthesis of Deoxyglycosides from Glycals Using B(C6F5)3 as Catalyst
- 2019
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:5, s. 2415-2424
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Tidskriftsartikel (refereegranskat)abstract
- B(C6F5)3 enables the metal-free unprecedented substrate-controlled direct α-stereoselective synthesis of deoxyglycosides from glycals. 2,3-Unsaturated α-O-glycoside products are obtained with deactivated glycals at 75 °C in the presence of the catalyst, while 2-deoxyglycosides are formed using activated glycals that bear no leaving group at C-3 at lower temperatures. The reaction proceeds in good to excellent yields via concomitant borane activation of glycal donor and nucleophile acceptor. The method is exemplified with the synthesis of a series of rare and biologically relevant glycoside analogues.
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| 42. |
- Schembri, Luke S, et al.
(författare)
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Palladium(0)-Catalyzed Carbonylative Synthesis of N-Acylsulfonamides via Regioselective Acylation
- 2019
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:11, s. 6970-6981
-
Tidskriftsartikel (refereegranskat)abstract
- N-Acylsulfonamides represent an important bioisostere of carboxylic acids that allow for greater molecular elaboration and enhanced hydrogen bonding capabilities. Herein, we present a mild and convenient palladium(0)-catalyzed synthesis of N-acylsulfonamides via the carbonylative coupling of sulfonyl azides and electron-rich heterocycles. The reaction proceeds via in situ generation of a sulfonyl isocyanate followed by regioselective acylation of an indole or pyrrole nucleophile. This approach has been used to synthesize 34 indole- and pyrrole-substituted N-acylsulfonamides in yields of up to 95%. Importantly, this process is ligand-free and compatible with an ex situ solid CO source and requires only slightly elevated temperatures, making it a highly attractive method for the preparation of this important class of compounds. This study further investigated the possibility of labeling N-acylsulfonamides with carbon-11 to facilitate biological evaluation and in vivo studies with positron emission tomography.
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| 43. |
- Schulz, Nils, et al.
(författare)
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NMR Determination of the Binding Constant of Ionic Species : A Caveat
- 2018
-
Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 83:18, s. 10881-10886
-
Tidskriftsartikel (refereegranskat)abstract
- Determination of the dissociation constant of ionic complexes with the standard NMR titration and NMR dilution techniques may yield a severely compromised result, due to the typically unconsidered chemical shift alteration induced by the gradual change of the ionic strength during the experiment. We show that the reliability of an NMR titration experiment is markedly improved upon keeping the overall ionic strength constant.
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| 44. |
- Shen, Zhengnan, et al.
(författare)
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Synthesis of β-(1→2)-Linked 6-Deoxy-L-altropyranose Oligosaccharides via Gold(I)-Catalyzed Glycosylation of an ortho-Hexynylbenzoate Donor
- 2017
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:6, s. 3062-3071
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Tidskriftsartikel (refereegranskat)abstract
- The ss-(1 -> 2)-linked 6-deoxy-L-altropyranose di- to pentasaccharides 2-5, relevant to the O-antigen of the infectious Yersinia enterocolitica 0:3, were synthesized for the first time. The challenging 1,2-cis-altropyranosyl linkage was assembled effectively via glycosylation with 2-O-benzyl-3,4-di-O-benzoyl-6-deoxy-L-altropyranosyl ortho-hexynylbenzoate (7) under the catalysis of PPh3AuNTf2. NMR and molecular modeling studies showed that the pentasaccharide (5) adopted a left-handed helical conformation. [GRAPHICS]
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| 45. |
- Shukla, Lakshmi, et al.
(författare)
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Synthesis and Spectroscopic Properties of Fluorinated Coumarin Lysine Derivatives
- 2018
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 83:8, s. 4792-4799
-
Tidskriftsartikel (refereegranskat)abstract
- The site-selective incorporation of fluorescent amino acids into proteins has emerged as a valuable alternative to expressible protein reporters. For successful application, a robust and scalable, yet flexible, route to non-natural amino acids is required. This work describes an improved synthesis of coumarin-conjugated lysine derivatives where fluorinated variants are accessed. These analogues can be utilized at low pH and should find application probing biological processes that operate under acidic conditions.
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| 46. |
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| 47. |
- Singh, Vijay P, et al.
(författare)
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Effect of a Bromo Substituent on the Glutathione Peroxidase Activity of a Pyridoxine-like Diselenide
- 2015
-
Ingår i: The Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 50:15, s. 7385-7395
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Tidskriftsartikel (refereegranskat)abstract
- In search for better mimics of the glutathioneperoxidase enzymes, pyridoxine-like diselenides 6 and 11,carrying a 6-bromo substituent, were prepared. Reaction of2,6-dibromo-3-pyridinol 5 with sodium diselenide provided 6via aromatic nucleophilic substitution of the 2-bromosubstituent. LiAlH4 caused reduction of all four ester groupsand returned 11 after acidic workup. The X-ray structure of 6showed that the dipyridyl diselenide moiety was kept in analmost planar, transoid conformation. According to NBOanalysis,this was due to weak intramolecular Se···O (1.1 kcal/mol) and Se···N-interactions (2.5 kcal/mol). That the 6-bromo substituent increased the positive charge on seleniumwas confirmed by NPA-analysis and seen in calculated andobserved 77Se NMR-shifts. Diselenide 6 showed a more than 3-fold higher reactivity than the corresponding des-bromocompound 3a and ebselen when evaluated in the coupled reductase assay. Experiments followed for longer time (2 h) confirmedthat diselenide 6 is a better GPx-catalyst than 11. On the basis of 77Se-NMR experiments, a catalytic mechanism for diselenide 6was proposed involving selenol, selenosulfide and seleninic acid intermediates. At low concentration (10 μM) where it showedonly minimal toxicity, it could scavenge ROS produced by MNC- and PMNC-cells more efficiently than Trolox.
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| 48. |
- Singh, Vijay P., et al.
(författare)
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Nitro-, Azo-, and Amino Derivatives of Ebselen : Synthesis, Structure, and Cytoprotective Effects
- 2017
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:1, s. 313-321
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Tidskriftsartikel (refereegranskat)abstract
- Novel azo-bis-ebselen compounds 7 were prepared by reduction of 7-nitro-2-aryl-1,2-benzisoselenazol-3(2H)ones 3 and 6 with sodium benzenetellurolate; NaTeC6H5, and by reaction of 2-bromo-3-nitrobenzamides with Na2Se2. The X-ray structure of 7b showed that the molecule, due to strong intramolecular secondary Se center dot center dot center dot N interactions, is completely planar. Azo-compounds 7 upon further reaction with NaTeC6H5 were reductively cleaved to provide 2 equiv of the corresponding aromatic amine. The weak Se-N bond was not stable enough to survive the reaction conditions, and diselenides 8 were isolated after workup. Whereas azo-bis-ebselens 7 were poor mimics of the glutathione peroxidase (GPx)-enzymes, nitroebselens 3, 6, and 11b and diselenides 8 were 3-6-fold more active than ebselen. Based on Se-77 NMR. spectroscopy, a catalytic cycle for diselenide 8b, involving aminoebselen 14, was proposed. As assessed by chemiluminescence measurements, the good GPx-mimics could reduce production of reactive oxygen species (ROS) in stimulated human mononuclear cells more efficiently than Trolox. No toxic effects of the, compounds were seen in MC3T3-cells at 25 mu M.
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| 49. |
- Stenlid, Joakim H., et al.
(författare)
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Nucleophilic Aromatic Substitution Reactions Described by the Local Electron Attachment Energy
- 2017
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 82:6, s. 3072-3083
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Tidskriftsartikel (refereegranskat)abstract
- A local multiorbital electrophilicity descriptor, the local electron attachment energy [E(r)], is used to study the nucleophilic aromatic substitution reactions of SNAr and VNS (vicarious nucleophilic substitution). E(r) considers all virtual orbitals below the free electron limit and is determined on the molecular isodensity contour of 0.004 atomic units. Good (R-2 = 0.83) to excellent (R-2 = 0.98) correlations are found between descriptor values and experimental reactivity data for six series of electron deficient arenes. These include homo- and heteroarenes, rings of five to six atoms, and a variety of fluorine, bromine, and hydride leaving groups. The solvent, temperature, and nucleophile are in addition varied across the series. The surface E(r) [E-s(r)] is shown to provide reactivity predictions better than those of transition-state calculations for a concerted SNAr reaction with a bromine substantially stronger than those of LUMO energies, and is overall more reliable than the molecular electrostatic potential. With the use of E-s(r), one can identify the various electrophilic sites within a molecule and correctly predict isomeric distributions. Since the calculations of E-s(r) are computationally inexpensive, the descriptor offers fast but accurate reactivity predictions for the important nucleophilic aromatic substitution class of reactions. Applications in, e.g., drug discovery, synthesis, and toxicology studies are envisaged.
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| 50. |
- Syrén, Per-Olof
(författare)
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Enzymatic Hydrolysis of Tertiary Amide Bonds by anti Nucleophilic Attack and Protonation
- 2018
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 83:21, s. 13543-13548
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Tidskriftsartikel (refereegranskat)abstract
- The molecular mechanisms conferring high resistance of planar tertiary amide bonds to hydrolysis by most enzymes have remained elusive. To provide a chemical explanation to this unresolved puzzle, UB3LYP calculations were performed on an active site model of Xaa-Pro peptidases. The calculated reaction mechanism demonstrates that biocatalysts capable of tertiary amide bond hydrolysis capitalize on anti nucleophilic attack and protonation of the amide nitrogen, in contrast to the traditional syn displayed by amidases and proteases acting on secondary amide bonds.
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