714 research outputs found
Development of a Continuous Photochemical Benzyne-Forming Process
A continuous-flow process is presented that enables the safe generation and derivatization of benzyne under photochemical conditions. This is facilitated by a new high-power LED lamp emitting light at 365 nm. The resulting flow process effectively controls the release of gaseous by-products based on an adjustable backpressure regulator and delivers a series of heterocyclic products in a short residence time of 3 minutes. The robustness of this methodology is demonstrated for the rapid generation of benzotriazoles, 2H-indazoles and various furan-derived adducts, facilitating the preparation of these important heterocyclic scaffolds via a simple and readily scalable flow protocol
Synthesis of Tetracyclic 2,3-Dihydro-1,3-diazepines from a Dinitrodibenzothiophene Derivative
Triply fused 1,3-diazepine derivatives have been obtained by acidic reduction of rotationally locked and sterically hindered nitro groups in the presence of an aldehyde or ketone. The nitro groups are sited on adjacent rings of a dicyanodibenzothiophene-5,5-dioxide, which also displays fully reversible two-electron-accepting behavior. The synthesis, crystallographically determined molecular structures, and aspects of the electronic properties of these new molecules are presented
Acetonitrile[2-({bis[2,4,6-tris(trifluoridomethyl)phenyl]phosphanyloxy}methyl)pyridine]methylpalladium(II) hexafluoroantimonate dichloromethane hemisolvate
In the title compound, [Pd(CH3)(C24H10F18NOP)(CH3CN)][SbF6]·0.5CH2Cl2, the PdII atom has a distorted square-planar environment being coordinated by an acetonitrile N atom [Pd—N = 2.079 (3) Å], a methyl C atom [Pd—C = 2.047 (4) Å] and the bidentate ligand 2-({[2,4,6-tris(trifluoromethyl)phenyl]phosphanyloxy}methyl)pyridine (L). In L, the short distance of 3.621 (3) Å between the centroids of pyridine and benzene rings indicates the presence of a π–π interaction. The crystal packing exhibits weak intermolecular C—H⋯F contacts. The solvent molecule has been treated as disordered between two positions of equal occupancy related by an inversion center
Excitation modulation of Eu:BPEPC based complexes as low-energy reference standards for circularly polarised luminescence (CPL)
Direct Amidation of Amino Acid Derivatives Catalyzed by Arylboronic Acids: Applications in Dipeptide Synthesis
The direct amidation of amino acid derivatives catalyzed by arylboronic acids has been examined. The reaction was generally slow relative to simple amine-carboxylic acid combinations though proceeded at 65–68 °C generally avoiding racemization. 3,4,5-Trifluorophenylboronic and o-nitrophenylboronic acids were found to be the best catalysts, though for slower dipeptide formations, high catalyst loadings were required and an interesting synergistic catalytic effect between two arylboronic acids was discovered
Error estimates for solid-state density-functional theory predictions: an overview by means of the ground-state elemental crystals
Predictions of observable properties by density-functional theory
calculations (DFT) are used increasingly often in experimental condensed-matter
physics and materials engineering as data. These predictions are used to
analyze recent measurements, or to plan future experiments. Increasingly more
experimental scientists in these fields therefore face the natural question:
what is the expected error for such an ab initio prediction? Information and
experience about this question is scattered over two decades of literature. The
present review aims to summarize and quantify this implicit knowledge. This
leads to a practical protocol that allows any scientist - experimental or
theoretical - to determine justifiable error estimates for many basic property
predictions, without having to perform additional DFT calculations. A central
role is played by a large and diverse test set of crystalline solids,
containing all ground-state elemental crystals (except most lanthanides). For
several properties of each crystal, the difference between DFT results and
experimental values is assessed. We discuss trends in these deviations and
review explanations suggested in the literature. A prerequisite for such an
error analysis is that different implementations of the same first-principles
formalism provide the same predictions. Therefore, the reproducibility of
predictions across several mainstream methods and codes is discussed too. A
quality factor Delta expresses the spread in predictions from two distinct DFT
implementations by a single number. To compare the PAW method to the highly
accurate APW+lo approach, a code assessment of VASP and GPAW with respect to
WIEN2k yields Delta values of 1.9 and 3.3 meV/atom, respectively. These
differences are an order of magnitude smaller than the typical difference with
experiment, and therefore predictions by APW+lo and PAW are for practical
purposes identical.Comment: 27 pages, 20 figures, supplementary material available (v5 contains
updated supplementary material
Diaquabis(dimethyl sulfoxide-κO)bis(saccharinato-κN)cobalt(II)
The title complex, [Co(C7H4NO3S)2(C2H6OS)2(H2O)2], contains a Co2+ cation in an octahedral coordination environment. The metal atom is surrounded by two different neutral ligands, namely dimethylsulfoxide (DMSO) and water, each coordinating through the O atom. The anionic saccharinate (sac; 1,1,3-trioxo-2,3-dihydro-1λ6,2-benzothiazol-2-ide) ligand coordinates through the N atom. Each of the three similar ligand pairs is in a trans configuration with respect to each other. The Co atom lies on a crystallographic center of symmetry and the octahedral geometry is not significantly distorted. A short O—H⋯O hydrogen bond is present between a water H atom and the ketone O atom; two longer hydrogen bonds (intra- and intermolecular) are also present between a water H and a sulfonic O atom, forming a supramolecular assembly through head-to-tail aggregation between adjacent complexes
Approaches to Styrenyl Building Blocks for the Synthesis of Polyene Xanthomonadin and its Analogues
A number of aryl building blocks for the synthesis of two xanthomonadin natural product pigments, as well as a related analogue, were accessed using a divergent hydroboration/bromoboration approach from a key alkynyl intermediate. A new approach towards substitution patterns around the ring was adopted following the isolation of an unexpected regioisomer from the bromination reaction. Potential coupling reactions onto these building blocks were explored, with a successful Sonogashira coupling performed on the key alkynyl intermediate, and with the key debrominated styrenyl boronate ester intermediate functionalised both by preliminary Suzuki–Miyaura coupling and by iododeboronation/Heck–Mizoroki coupling. Coupling reactions with brominated styrenyl intermediates proved much more challenging due to the instability of the intermediates to cross‐coupling, but some studies have shown promise
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