1,720,973 research outputs found
Regioselective Synthesis of bis α-Acyloxy 1,4- and 1,5-Diketones from 1,5- and 1,6-Dienes
No full textPyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans
No full textA thorough investigation of the minor oxidation products of two penta-tetrahydrofuran compounds with pyridinium chlorochromate has been carried out. Isolation of ring-B oxygenated spiroketal and degradation products, including polycyclic mono- and bis-lactone compounds, supports the previously postulated involvement of cyclic enolether intermediates in the oxidation of THF and poly-THF substances with PCC. Based on the collected evidence, a new mechanistic route for the PCC-mediated oxidative cleavage of α-hydroxy-THF compounds to γ-lactones has been postulated. The proposed mechanism well agrees with the one reported for the oxidative cleavage of 8-hydroxy-neoisocedranol oxide by RuO4, a fact that further supports our previous observation on the similar oxidizing behaviour shown by PPC and RuO4 towards THFcontaining compounds
Synthesis, stereostructure and H-bonding patterns of a tris-THF compound
No full textThe synthesis and crystallog. anal. of a new tris-THF compd., obtained by chem. degrdn. of a penta-THF precursor, is reported. The mol. structure of the tris-THF compd. allows to definitively assess the stereoconfiguration of the parent penta-THF compd., that was known only partially. The tris-THF compd. crystallizes in the monoclinic space group C2/c with a = 21.621(8), b = 7.481(4), c = 30.801(9) Å, β = 94.08(3)°, Z = 8. The final refinement converged to R 1 = 0.0804 for 1,706 independent obsd. reflections having I > 2σ(I). The tris-THF compd. adopts in the solid state a flexuous and wavy conformation due to the cis-trans-trans configuration of the three THF rings and to intramol. H bonding. Mols. in the crystals form H-bonded chains that are wrapped around the crystallog. binary screw axes. The chains are also bonded to each other by H-bonding through and ring motifs. Graphical Abstr. The tris-THF compd. adopts in the solid state a flexuous and wavy conformation due to the cis-trans-trans configuration of the three THF rings and to intramol. H bonding. Mols. in the crystals form H-bonded chains that are wrapped around the crystallog. binary screw axes
(3R,3aR,6R,6aR)-Hexahydrofuro[3,2-b]furan-3,6-diyl dibenzoate
No full textThe title compound, C20H18O6, prepared from d-mannitol by a two-step procedure, is a functionalized fused bis-tetrahydrofuran. In the central fragment, consisting of two fused tetrahydrofuran rings, one O atom and its two adjacent C atoms, a methylene and a bridgehead C atom, are disordered over two sets of sites with an occupancy ratio of 0.735 (9):0.265 (9). In the major component, the ring containing the disordered O atom is a half-chair conformation with twisted methylene and benzoate-substituted C atoms, whereas the other ring has a half-chair or T-form conformation. In the minor component, the ring with the disordered O atom has an envelope conformation, with the O atom as the flap, and the other ring has a half-chair conformation, with the O atom and the other bridgehead CH atom being twisted. The two aromatic rings are inclined to one another by 20.00 (12)°. In the crystal, adjacent molecules are linked via C—H...π interactions, forming chains propagating along [010]
(3S,3aS,6R,6aR)-2-Oxohexahydrofuro[3,2-b]furan-3,6-diyl dibenzoate
No full textThe title compound, C20H16O7, contains a cis-fused γ-lactone tetrahydrofuran ring system functionalized with two benzoyloxy groups. Both rings adopt an envelope conformation. The molecule assumes an elongated shape and exibits non-crystallographic C2 symmetry. The benzoyloxy groups are almost planar [maximum deviations of 0.0491 (15) and 0.0336 (17) Å for the O atoms] and their mean planes are inclined to one another by 16.51 (4)°. The crystal packing features weak C—H...O interactions. The aryl groups of adjacent molecules are parallel shifted with face-to-face contacts and a shortest intermolecular C...C distance of 3.482 (4) Å
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A General Synthesis of Bis-α-acyloxy-1,4- and -1,5-diketones Through Catalytic Oxidative Opening of Acylated THF and THP Diols
No full textThe first general synthesis of bis-α-acyloxy-1,4- and -1,5-di ketones has been accomplished in a catalytic oxidative open ing of bis-acylated THF and THP (tetrahydropyran) diols, which were synthesised by osmium- or ruthenium-catalysed oxidative cyclisation of 1,5- and 1,6-dienes. The overall sequence corresponds to the regioselective double ketoacylox-ylation of the starting diene. The synthesised bis-α-acyloxy-1,5-dicarbonyl compounds have been transformed into pyridine-based oxido pincer ligands or pyrazinedimethanol substances, leading to the discovery of unprecedented aromatisation routes
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