The Structural Basis for Hydrolysis Resistance in the Esters of (2-Formylphenyl)boronic Acid 2,4-Dinitrophenylhydrazones

2002 ◽  
Vol 67 (7) ◽  
pp. 1084-1094 ◽  
Author(s):  
Michael P. Groziak ◽  
Paul D. Robinson
Keyword(s):  
Boronic Acid ◽  
Intramolecular Interaction ◽  
Boronic Acids ◽  
Membered Ring ◽  
Structural Basis ◽  
Previous Suggestion ◽  
Boronate Esters ◽  
X Ray ◽  
Hydrolysis Resistance ◽  
Electron Deficiency

Under conditions that typically afford bicyclic boron heterocycles directly, (2-formylphenyl)boronic acids react with 2,4-dinitrophenylhydrazine in ethanol to give highly waterresistant diethyl boronate esters. Two such 2,4-dinitrophenylhydrazones were prepared and their X-ray crystal structures determined. Contrary to a previous suggestion that their unusual stability is due to an intramolecular N→B coordination giving a six-membered BN2C3 ring system based on a (Z)-hydrazone, these compounds instead were found to be (E)-hydrazones internally stabilized by a weak intramolecular interaction between nitrogen and boron from within a five-membered ring. Further study revealed that the electron deficiency of the starting hydrazine reagent plays a key role in determining the structure of the hydrazone isolated, and that the water-resistant boronate esters can be hydrolyzed under forcing conditions to the boronic acids.

Stereoselective addition of acetone to the C=N bond of [4.3.0] boron heterobicycles

2001 ◽  
Vol 79 (8) ◽  
pp. 1229-1237 ◽  
Author(s):  
Victor Barba ◽  
Damian Cuahutle ◽  
Rosa Santillan ◽  
Norberto Farfán
Keyword(s):  
Solid State ◽  
Schiff Bases ◽  
Boronic Acid ◽  
Boronic Acids ◽  
Tridentate Ligands ◽  
X Ray ◽  
Dimeric Structure ◽  
Stereoselective Addition ◽  
Phenyl Boronic Acid ◽  
Boron Complexes

The reaction of N-salicylidene-2-aminophenolate (SAP-H2) derivatives with phenyl boronic acid afforded five new boron bicyclic species in moderate yields, as confirmed by an X-ray study of the boron heterocycle derived from 2-amino-4-chlorophenol. The results also showed that the boron complexes derived from Schiff bases undergo an acetolysis reaction to give the corresponding dioxazaborocines containing all substituents on the same side also in good yields. The structure of one of the addition products was established by X-ray analysis showing that, in the solid state, it exists as a dimeric structure formed by hydrogen bonds.Key words: borocines, tridentate ligands, imines, boronic acids.

Electron diffraction detection of ordliking in annealed PbTe thin film

1990 ◽  
Vol 48 (4) ◽  
pp. 1018-1019
Author(s):  
Karimat El-Sayed
Keyword(s):  
Thin Film ◽  
Electron Diffraction ◽  
Lead Telluride ◽  
Structural Basis ◽  
Face Centered Cubic ◽  
X Ray ◽  
Polycrystalline Thin Films ◽  
Stage Process ◽  
Diffraction Patterns ◽  
Face Centered

Lead telluride is an important semiconductor of many applications. Many Investigators showed that there are anamolous descripancies in most of the electrophysical properties of PbTe polycrystalline thin films on annealing. X-Ray and electron diffraction studies are being undertaken in the present work in order to explain the cause of this anamolous behaviour.Figures 1-3 show the electron diffraction of the unheated, heated in air at 100°C and heated in air at 250°C respectively of a 300°A polycrystalline PbTe thin film. It can be seen that Fig. 1 is a typical [100] projection of a face centered cubic with unmixed (hkl) indices. Fig. 2 shows the appearance of faint superlattice reflections having mixed (hkl) indices. Fig. 3 shows the disappearance of thf superlattice reflections and the appearance of polycrystalline PbO phase superimposed on the [l00] PbTe diffraction patterns. The mechanism of this three stage process can be explained on structural basis as follows :

scholarly journals Structural basis of the stereoselective formation of the spirooxindole ring in the biosynthesis of citrinadins

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zhiwen Liu ◽  
Fanglong Zhao ◽  
Boyang Zhao ◽  
Jie Yang ◽  
Joseph Ferrara ◽  
...  
Keyword(s):  
High Resolution ◽  
Organic Synthesis ◽  
Indole Alkaloids ◽  
Site Directed Mutagenesis ◽  
Structural Basis ◽  
Directed Mutagenesis ◽  
Computational Studies ◽  
X Ray ◽  
Evolutionary Branch ◽  
Catalytic Mechanisms

AbstractPrenylated indole alkaloids featuring spirooxindole rings possess a 3R or 3S carbon stereocenter, which determines the bioactivities of these compounds. Despite the stereoselective advantages of spirooxindole biosynthesis compared with those of organic synthesis, the biocatalytic mechanism for controlling the 3R or 3S-spirooxindole formation has been elusive. Here, we report an oxygenase/semipinacolase CtdE that specifies the 3S-spirooxindole construction in the biosynthesis of 21R-citrinadin A. High-resolution X-ray crystal structures of CtdE with the substrate and cofactor, together with site-directed mutagenesis and computational studies, illustrate the catalytic mechanisms for the possible β-face epoxidation followed by a regioselective collapse of the epoxide intermediate, which triggers semipinacol rearrangement to form the 3S-spirooxindole. Comparing CtdE with PhqK, which catalyzes the formation of the 3R-spirooxindole, we reveal an evolutionary branch of CtdE in specific 3S spirocyclization. Our study provides deeper insights into the stereoselective catalytic machinery, which is important for the biocatalysis design to synthesize spirooxindole pharmaceuticals.

Synthesis, characterization and X-ray studies of new chiral five-six-membered ring, [4.3.0] heterobicyclic system of monomeric boronates

2011 ◽  
Vol 696 (11-12) ◽  
pp. 2420-2428 ◽  
Author(s):  
José María Rivera ◽  
Susana Rincón ◽  
Norberto Farfán ◽  
Rosa Santillan
Keyword(s):  
Membered Ring ◽  
X Ray

Bestimmung von innermolekularen Torsionswinkeln aus Hyperfeinstruktur-Aufspaltungen und g-Faktoren

1965 ◽  
Vol 20 (9) ◽  
pp. 1117-1121 ◽  
Author(s):  
K. Möbius
Keyword(s):  
Electron Diffraction ◽  
Aromatic Hydrocarbon ◽  
Aromatic Hydrocarbons ◽  
Small Amplitude ◽  
Membered Ring ◽  
Radical Ions ◽  
Hydrogen Atoms ◽  
Stereochemical Structure ◽  
X Ray ◽  
Phenyl Rings

The stereochemical structure of aromatic hydrocarbons in solution being overcrowded with hydrogen atoms is not known with certainty, because the conventional X-ray and electron diffraction methods are suitable only for samples in the crystalline and vapor phase. Using EPR spectroscopy for the aromatic hydrocarbon radicals biphenyl (—), phenanthrene (—) and pentaphenylcyclopentadienyl (PPCPD) innermolecular twist and bond angles could be determined by means of hfssplittings and g-factors. Stably solvated biphenyl radical ions are found to have twist angles of 38 ±2°; phenanthrene ions turn out to be planar but change their angles of hybridization at particular positions; in the PPCPD radical the phenyl rings oscillate with small amplitude around planes orthogonal to the five-membered ring.

X-Ray crystallographic study of a 1,3,2-dioxaphosphorinane dimer containing five-coordinated phosphorus in the 12-membered ring

1993 ◽  
Vol 4 (2-3) ◽  
pp. 271-278 ◽  
Author(s):  
Yande Huang ◽  
Alan E. Sopchik ◽  
Atta M. Arif ◽  
Wesley G. Bentrude
Keyword(s):  
Membered Ring ◽  
X Ray ◽  
Crystallographic Study

scholarly journals Five-membered ring annelation in [2.2]paracyclophanes by aldol condensation

2014 ◽  
Vol 10 ◽  
pp. 2021-2026 ◽  
Author(s):  
Henning Hopf ◽  
Swaminathan Vijay Narayanan ◽  
Peter G Jones
Keyword(s):  
Structural Analysis ◽  
Spectroscopic Data ◽  
Acid Treatment ◽  
Aldol Condensation ◽  
Membered Ring ◽  
X Ray

Under basic conditions 4,5,12,13-tetraacetyl[2.2]paracyclophane (9) cyclizes by a double aldol condensation to provide the two aldols 12 and 15 in a 3:7 ratio. The structures of these compounds were obtained from X-ray structural analysis, spectroscopic data, and mechanistic considerations. On acid treatment 12 is dehydrated to a mixture of the condensed five-membered [2.2]paracyclophane derivatives 18–20, whereas 15 yields a mixture of the isomeric cyclopentadienones 21–23. The structures of these elimination products are also deduced from X-ray and spectroscopic data. The sequence presented here constitutes the simplest route so far to cyclophanes carrying an annelated five-membered ring.

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