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- Moberg, C, et al.
(författare)
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Selectivity and reactivity in asymmetric allylic alkylation
- 1999
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Ingår i: Pure and Applied Chemistry. - Royal Inst Technol, Dept Chem, SE-10044 Stockholm, Sweden. Royal Danish Sch Pharm, DK-2100 Copenhagen, Denmark. Uppsala Univ, Ctr Biomed, Dept Organ Pharmaceut Chem, SE-75123 Uppsala, Sweden. Stockholm Univ, Arrhenius Lab, Dept Struct Chem, SE-10691 Stockholm, Sweden. : Walter de Gruyter GmbH. - 0033-4545 .- 1365-3075. ; 71:8, s. 1477-1483
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Tidskriftsartikel (refereegranskat)abstract
- 2-(1-Hydroxyalkyl)-6-oxazolyl-and 2-(1-alkoxyalkyl)-6-oxazolylpyridines serve as versatile ligands in the palladium-catalyzed allylic substitution of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. The enantioselectivity of the reaction is dependent on the conformation of the ligands, as deduced by NMR, X-ray crystallography and DFT calculations of palladium(II) complexes of the ligands. The reactions are slow, requiring up to four days reaction time. However, with the use of microwave flash heating, reaction times are reduced to 2 min, with only minor loss in stereoselectivity.
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- Paavola, Sari, et al.
(författare)
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Aerobic oxidation of 1-phenylethanol catalyzed by palladaheterocycles
- 2004
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Ingår i: Advanced Synthesis and Catalysis. - : Wiley. - 1615-4150 .- 1615-4169. ; 346:2-3, s. 237-244
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Tidskriftsartikel (refereegranskat)abstract
- Cyclometallated palladium compounds with pyridine were shown to serve as more efficient catalysts for the aerobic oxidation of 1-phenylethanol than a previously investigated analogue with an oxazoline ring. Substituents with different electronic properties in the phenyl ring were shown to exhibit an only minor influence on the reactivity of the catalytic system. The first step in the reaction consists of the splitting of the acetate bridge in the dimeric starting complex and coordination of a ligand to palladium. By ab initio calculations it was shown that, in the presence of solvent, a complex with pyridine was more stable than that with the alcohol, whereas the opposite situation was found in the gas phase. The complex with coordinated alcohol was stabilized by hydrogen bonding. Good agreement was found between the computed structure and the X-ray structure of the initial palladaheterocycle 1.
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- Szabo, Zoltan, et al.
(författare)
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Combinatorial multinuclear NMR and X-ray diffraction studies of uranium(VI)-nucleotide complexes
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 127:43, s. 15236-15247
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Tidskriftsartikel (refereegranskat)abstract
- The complex formation of uranium(VI) with four nucleoticles, adenosine- (AMP), guanosine(GMP), uridine- (UMP), and cyticline-monophosphate (CMP), has been studied in the alkaline pH range (8.5-12) by H-1, P-31, C-13, and O-17 NMR spectroscopy, providing spectral integral, chemical shift, homo and heteronuclear coupling, and diffusion coefficient data. We find that two and only two complexes are formed with all ligands in the investigated pH region independently of the total uranium(VI) and ligand concentrations. Although the coordination of the 5'-phosphate group and the 2'- and 3'-hydroxyl groups of the sugar unit to the uranyl ions is similar to that proposed earlier (Feldman complex), the number and the structures of the complexes are different. The uranium-to-nucleotide ratio is 6:4 in one of the complexes and 3:3 in the other one, as unambiguously determined by a combinatorial approach using a systematic variation of the ratio of two ligands in ternary uranium(VI)-nucleotide systems. The structure of the 3:3 complex has been determined by single-crystal diffraction as well, and the results confirm the structure proposed by NMR in aqueous solution. The results have important implications on the synthesis of oligonucleotides.
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