| 1. |
- Akkarasamiyo, Sunisa, et al.
(författare)
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Tsuji-Trost Reaction of Non-Derivatized Allylic Alcohols
- 2018
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 24:14, s. 3488-3498
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Tidskriftsartikel (refereegranskat)abstract
- Palladium-catalyzed allylic substitution of non-derivatized enantioenriched allylic alcohols with a variety of uncharged N-, S-, C- and O-centered nucleophiles using a bidentate BiPhePhos ligand is described. A remarkable effect of the counter ion (X) of the XPd[kappa(2)-BiPhePhos][kappa(3)-C3H5] was observed. When ClPd[kappa(2)-BiPhePhos][eta(3)-C3H5] (complexI) was used as catalyst, non-reproducible results were obtained. Study of the complex by X-ray crystallography, (PNMR)-P-31 spectroscopy, and ESI-MS showed that a decomposition occurred where one of the phosphite ligands was oxidized to the corresponding phosphate, generating ClPd[kappa(1)-BiPhePhosphite-phosphate][eta(3)-C3H5] species (complexII). When the chloride was exchanged to the weaker coordinating OTf- counter ion the more stable Pd[kappa(2)-BiPhePhos][eta(3)-C3H5](+)+[OTf] (-) (complexIII) was formed. ComplexIII performed better and gave higher enantiospecificities in the substitution reactions. ComplexIII was evaluated in Tsuji-Trost reactions of stereogenic non-derivatized allylic alcohols. The desired products were obtained in good to excellent yields (71-98%) and enantiospecificities (73-99%) for both inter- and intramolecular substitution reactions with only water generated as a by-product. The methodology was applied to key steps in total synthesis of (S)-cuspareine and (+)-lentiginosine. A reaction mechanism involving a palladium hydride as a key intermediate in the activation of the hydroxyl group is proposed in the overall transformation.
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| 2. |
- 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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| 3. |
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| 4. |
- Eriksson, Jonas, et al.
(författare)
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Synthesis and preclinical evaluation of the CRTH2 antagonist [11C]MK-7246 as a novel PET tracer and potential surrogate marker for pancreatic beta-cell mass
- 2019
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Ingår i: Nuclear Medicine and Biology. - : Elsevier BV. - 0969-8051 .- 1872-9614. ; 71, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: MK-7246 is a potent and selective antagonist for chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). Within the pancreas CRTH2 is selectively expressed in pancreatic β-cells where it is believed to play a role in insulin release. Reduction in β-cell mass and insufficient insulin secretion in response to elevated blood glucose levels is a hallmark for type 1 and type 2 diabetes. Reported here is the synthesis of [11C]MK-7246 and initial preclinical evaluation towards CRTH2 imaging. The aim is to develop a method to quantify β-cell mass with PET and facilitate non-invasive studies of disease progression in individuals with type 2 diabetes.Methods: The precursor N-desmethyl-O-methyl MK-7246 was synthesized in seven steps and subjected to methylation with [11C]methyl iodide followed by hydrolysis to obtain [11C]MK-7246 labelled in the N-methyl position. Preclinical evaluation included in vitro radiography and immune-staining performed in human pancreatic biopsies. Biodistribution studies were performed in rat by PET-MRI and in pig by PET-CT imaging. The specific tracer uptake was examined in pig by scanning before and after administration of MK-7246 (1 mg/kg). Predicted dosimetry of [11C]MK-7246 in human males was estimated based on the biodistribution in rat.Results: [11C]MK-7246 was obtained with activities sufficient for the current investigations (270±120 MBq) and a radiochemical purity of 93±2%. The tracer displayed focal binding in areas with insulin positive islet of Langerhans in human pancreas sections. Baseline uptake in pig was significantly reduced in CRTH2-rich areas after administration of MK-7246; pancreas (66% reduction) and spleen (88% reduction). [11C]MK-7246 exhibited a safe human predicted dosimetry profile as extrapolated from the rat biodistribution data.Conclusions: Initial preclinical in vitro and in vivo evaluation of [11C]MK-7246 show binding and biodistribution properties suitable for PET imaging of CRTH2. Further studies are warranted to assess its potential in β-cell mass imaging and CRTH2 drug development.
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| 5. |
- Galkin, Maxim V., et al.
(författare)
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Mild Heterogeneous Palladium-Catalyzed Cleavage of beta-O-4 '-Ether Linkages of Lignin Model Compounds and Native Lignin in Air
- 2014
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 6:1, s. 179-184
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Tidskriftsartikel (refereegranskat)abstract
- A mild and robust heterogeneous palladium-catalyzed CO bond cleavage of 2-aryloxy-1-arylethanols using formic acid as reducing agent in air was developed. The cleaved products were isolated in 92-98% yield; and by slightly varying the reaction conditions, a ketone, an alcohol, or an alkane can be generated in near-quantitative yield. This reaction is applicable to cleaving the -O-4-ether bond found in lignin polymers of different origin. The reaction was performed on a lignin polymer model to generate either the monomeric aryl ketone or alkane in a quantitative yield. Moderate depolymerization was achieved with native lignin at similar reaction conditions. Mechanistic studies under kinetic control indicate that an initial palladium-catalyzed dehydrogenation of the alcohol is followed by insertion of palladium to an enol equivalent. A palladium-formato complex reductively cleaves the palladium-enolate complex to generate the ketone.
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| 6. |
- Howard, Fredrick, et al.
(författare)
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A chemoselective route to either 4-methyl-2,4-diphenyl-2-pentene or 1,1,3-trimethyl-3-phenylindane from 2-phenylpropan-2-ol mediated by BiBr3 : a mechanistic study
- 2010
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Ingår i: Tetrahedron Letters. - : Elsevier BV. - 0040-4039 .- 1359-8562. ; 51:32, s. 4208-4210
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of 2-phenylpropan-2-ol mediated by BiBr3 can, through control of the temp., yield selectively either 4-methyl-2,4-diphenyl-2-pentene or 1,1,3-trimethyl-3-phenylindane. A reaction mechanism that proceeds via 1-methylstyrene is disclosed.
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| 7. |
- Olsen, Peter, et al.
(författare)
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Cyclic allylic carbonates as a renewable platform for protecting chemistry in water
- 2018
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 20:14, s. 3186-3190
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Tidskriftsartikel (refereegranskat)abstract
- The present work explores different cyclic allylic carbonates as a potential class of allylcarbamate precursors. The 5-membered carbonate formed a carbamate with very good thermal and pH stability, which could be cleanly deprotected in aqueous solution, in just 30 min with 2 mol% Pd(OAc)(2) as catalyst. The polar nature of the installed motif made it possible to deprotect highly unpolar substrates in water as solvent.
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| 8. |
- 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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| 9. |
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| 10. |
- Sawadjoon, Supaporn, et al.
(författare)
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An atom efficient route to N-aryl and N-alkyl pyrrolines by transition metal catalysis
- 2011
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Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 9:7, s. 2548-2554
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of N-aryl, N-tosyl, and N-alkyl pyrrolines from allyl alcohols and amines has been developed. The reaction sequence includes a palladium-catalyzed allylation step in which non-manipulated allyl alcohol is used to generate the diallylated amine in good to excellent yield. An excess of allyl alcohol was necessary for efficient diallylation of the amine, where the excess alcohol could be recycled three times. For aryl and tosyl amines, Pd[P(OPh)(3)](4) was used and for benzyl and alkyl amines a catalytic system comprising Pd(OAc)(2), (PBu3)-Bu-n, and BEt3 was used. Both the electronic properties and the steric influence of the amine affected the efficiency of the allylation. The isolated diallylated amines were transformed into their corresponding pyrrolines by ring-closing metathesis catalyzed by (H(2)IMes)(PCy3)Cl2RuCHPh in good to excellent yield. A one-pot reaction was developed in which aniline was transformed into the corresponding pyrroline without isolating the diallylated intermediate. This one-pot reaction was successfully scaled-up to 1 mL of aniline in which the N-phenyl pyrroline was isolated in 95% yield. The versatility of the reaction in which 3-methyl-1-phenyl pyrroline was prepared in two-steps was demonstrated.
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