Browse
Submit Data
Databases
API
Help

Dataset Information

28 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Wagner-Meerwein-Type Rearrangements of Germapolysilanes - A Stable Ion Study.

ABSTRACT: The rearrangement of tris(trimethylsilyl)silyltrimethylgermane 1 to give tetrakis(trimethylsilyl)germane 2 was investigated as a typical example for Lewis acid catalyzed Wagner-Meerwein-type rearrangements of polysilanes and polygermasilanes. Direct (29)Si NMR spectroscopic evidence is provided for several cationic intermediates during the reaction. The identity of these species was verified by independent synthesis and NMR characterization, and their transformation was followed by NMR spectroscopy.

SUBMITTER: Albers L

PROVIDER: S-EPMC4534834 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Wagner-Meerwein-Type Rearrangements of Germapolysilanes - A Stable Ion Study.

Albers Lena L Meshgi Mohammad Aghazadeh MA Baumgartner Judith J Marschner Christoph C Müller Thomas T

Organometallics 20150723 15

The rearrangement of tris(trimethylsilyl)silyltrimethylgermane 1 to give tetrakis(trimethylsilyl)germane 2 was investigated as a typical example for Lewis acid catalyzed Wagner-Meerwein-type rearrangements of polysilanes and polygermasilanes. Direct 29Si NMR spectroscopic evidence is provided for several cationic intermediates during the reaction. The identity of these species was verified by independent synthesis and NMR characterization, and their transformation was fo ...[more]

PMID: 26294805

Similar Datasets

Enantioselective Aryl-Iodide-Catalyzed Wagner-Meerwein Rearrangements.

Project description:We report a strategy for effecting catalytic, enantioselective carbocationic rearrangements through the intermediacy of alkyl iodanes as stereodefined carbocation equivalents. Asymmetric Wagner-Meerwein rearrangements of β-substituted styrenes are catalyzed by the C2-symmetric aryl iodide 1 to provide access to enantioenriched 1,3-difluorinated molecules possessing interesting and well-defined conformational properties. Hammett and kinetic isotope effect studies, in combination with computational investigations, reveal that two different mechanisms are operative in these rearrangement reactions, with the pathway depending on the identity of the migrating group. In reactions involving alkyl-group migration, intermolecular fluoride attack is product- and enantio-determining. In contrast, reactions in which aryl rearrangement occurs proceed through an enantiodetermining intramolecular 1,2-migration prior to fluorination. The fact that both pathways are promoted by the same chiral aryl iodide catalyst with high enantioselectivity provides a compelling illustration of generality across reaction mechanisms in asymmetric catalysis.

| S-EPMC7523190 | biostudies-literature

Dispersion-Energy-Driven Wagner-Meerwein Rearrangements in Oligosilanes.

Project description:The installation of structural complex oligosilanes from linear starting materials by Lewis acid induced skeletal rearrangement reactions was studied under stable ion conditions. The produced cations were fully characterized by multinuclear NMR spectroscopy at low temperature, and the reaction course was studied by substitution experiments. The results of density functional theory calculations indicate the decisive role of attractive dispersion forces between neighboring trimethylsilyl groups for product formation in these rearrangement reactions. These attractive dispersion interactions control the course of Wagner-Meerwein rearrangements in oligosilanes, in contrast to the classical rearrangement in hydrocarbon systems, which are dominated by electronic substituent effects such as resonance and hyperconjugation.

| S-EPMC4891741 | biostudies-literature

Experimental and theoretical studies on the Nazarov cyclization/Wagner-Meerwein rearrangement sequence.

Project description:Highly functionalized cyclopentenones can be generated by a chemoselective copper(II)-mediated Nazarov/Wagner-Meerwein rearrangement sequence of divinyl ketones. A detailed investigation of this sequence is described including a study of substrate scope and limitations. After the initial 4? electrocyclization, this reaction proceeds via two different sequential [1,2]-shifts, with selectivity that depends upon either migratory ability or the steric bulkiness of the substituents at C1 and C5. This methodology allows the creation of vicinal stereogenic centers, including adjacent quaternary centers. This sequence can also be achieved by using a catalytic amount of copper(II) in combination with NaBAr(4)(f), a weak Lewis acid. During the study of the scope of the reaction, a partial or complete E/Z isomerization of the enone moiety was observed in some cases prior to the cyclization, which resulted in a mixture of diastereomeric products. Use of a Cu(II)-bisoxazoline complex prevented the isomerization, allowing high diastereoselectivity to be obtained in all substrate types. In addition, the reaction sequence was studied by DFT computations at the UB3LYP/6-31G(d,p) level, which are consistent with the proposed sequences observed, including E/Z isomerizations and chemoselective Wagner-Meerwein shifts.

| S-EPMC3382077 | biostudies-literature

Palladium-catalyzed asymmetric ring expansion of allenylcyclobutanols: an asymmetric Wagner-Meerwein shift.

Project description:In this study, we developed a palladium-catalyzed atom economic asymmetric Wagner-Meerwein shift of allenylcyclobutanol substrates. It is an excellent method for creating functionalized cyclopentanones with an alpha-chiral O-tertiary center by ring expansion of allenylcyclobutanols. This reaction was initiated by hydropalladation and afforded excellent enantioselectivity as well as atom economy. This method provides an efficient route toward the synthesis of natural products such as trans-kumausyne's family, spiro ring systems. In addition, we obtained excellent diastereoselectivity and enantioselectivity at the same time by using 3-monosubstituted allenylcyclobutanol.

| S-EPMC2585988 | biostudies-literature

Sesquiterpene Cyclase BcBOT2 Promotes the Unprecedented Wagner-Meerwein Rearrangement of the Methoxy Group.

Project description:Presilphiperfolan-8β-ol synthase (BcBOT2), a substrate-promiscuous sesquiterpene cyclase (STC) of fungal origin, is capable of converting two new farnesyl pyrophosphate (FPP) derivatives modified at C7 of farnesyl pyrophosphate (FPP) bearing either a hydroxymethyl group or a methoxymethyl group. These substrates were chosen based on a computationally generated model. Biotransformations yielded five new oxygenated terpenoids. Remarkably, the formation of one of these tricyclic products can only be explained by a cationically induced migration of the methoxy group, presumably via a Meerwein-salt intermediate, unprecedented in synthetic chemistry and biosynthesis. The results show the great principle and general potential of terpene cyclases for mechanistic studies of unusual cation chemistry and for the creation of new terpene skeletons.

| S-EPMC11228982 | biostudies-literature

Efficient Nazarov cyclization/Wagner-Meerwein rearrangement terminated by a Cu(II)-promoted oxidation: synthesis of 4-alkylidene cyclopentenones.

Project description:The discovery and elucidation of a new Nazarov cyclization/Wagner-Meerwein rearrangement/oxidation sequence is described that constitutes an efficient strategy for the synthesis of 4-alkylidene cyclopentenones. DFT computations and EPR experiments were conducted to gain further mechanistic insight into the reaction pathways.

| S-EPMC3887475 | biostudies-literature

Understanding the fate of the oxyallyl cation following Nazarov electrocyclization: sequential Wagner-Meerwein migrations and the synthesis of spirocyclic cyclopentenones.

Project description:A general reaction sequence is described that involves Nazarov cyclization followed by two sequential Wagner-Meerwein migrations, to afford spirocyclic compounds from divinyl ketones in the presence of 1 equiv of copper(II) complexes. A detailed investigation of this sequence is described including a study of substrate scope and limitations. It was found that after 4? electrocyclization, two different pathways are available to the oxyallyl cation intermediate: elimination of a proton can give the usual Nazarov cycloadduct, or ring contraction can give an alternative tertiary carbocation. After ring contraction, either [1,2]-hydride or carbon migration can occur, depending upon the substitution pattern of the substrate, to furnish spirocyclic products. The rearrangement pathway is favored over the elimination pathway when catalyst loading is high and the copper(II) counterion is noncoordinating. Several ligands were found to be effective for the reaction. Thus, the reaction sequence can be controlled by judicious choice of reaction conditions to allow selective generation of richly functionalized spirocycles. The three steps of the sequence are stereospecific: electrocyclization followed by two [1,2]-suprafacial Wagner-Meerwein shifts, the ring contraction and then a hydride, alkenyl, or aryl shift. The method allows stereospecific installation of adjacent stereocenters or adjacent quaternary centers arrayed around a cyclopentenone ring.

| S-EPMC3104681 | biostudies-literature

Multimodal Imaging in Wagner Syndrome.

Project description:Wagner syndrome is a rare vitreoretinopathy described in a limited number of families. Here the authors describe four cases of suspected Wagner syndrome. All four cases had depressed rod and cone function on electroretinography, outer retinal disruption on spectral-domain optical coherence tomography, and constricted central visual fields with smaller isopter testing. Fundus autofluorescence performed in one patient highlighted a perivascular pattern to chorioretinal atrophy. Two patients had a history of uveitis with active cystoid macular edema. The diagnosis of Wagner syndrome was supported in three cases with genetic testing for VCAN mutations, whereas the other case harbored a variation of unknown significance in VCAN that may have been nonpathogenic. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:574-579.].

| S-EPMC5530878 | biostudies-literature

Iterative mass spectrometry and X-ray crystallography to study ion-trapping and rearrangements by a flexible cluster.

Project description:An important aspect of chemical reactions involves understanding the intermediate steps from reactants to products. The iterative use of mass spectrometry and X-Ray crystallography is demonstrated to be a powerful combination in this respect. We have applied them in identifying molecular clusters in solution followed by their solid-state structural characterizations. We used a key ligand, 2-[(2-hydroxy-3-methoxy-benzylidene)-amino]-ethanesulfonate (L), which serves as chelating/bridging units to stabilize the precursor [Li?Ni?(OH)?(L)?(CH?CN)?](ClO?)?·4CH?CN. The results of subsequent reactions witness a cascade of processes involving fragmentation, inner bridging ligand substitution (OH? to OCH??), changing modes of binding (chelate to monodentate) of the key ligand, ion-trapping and exchange (Li?, Na? and Ca²?) and their site preferences, coordinating and non-coordinating solvents (CH?CN to CH?OH, H?O and EtOH) replacement. The flexibility of the Ni?OL? species in solution permits the formation of six derivatives. The complimentary techniques open a broader prospect for cluster design and applications.

| S-EPMC3865461 | biostudies-literature

ROS1 genomic rearrangements are rare actionable drivers in microsatellite stable colorectal cancer.

Project description:c-Ros oncogene 1, receptor tyrosine kinase (ROS1) genomic rearrangements have been reported previously in rare cases of colorectal cancer (CRC), yet little is known about the frequency, molecular characteristics, and therapeutic vulnerabilities of ROS1-driven CRC. We analyzed a clinical dataset of 40 589 patients with CRC for ROS1 genomic rearrangements and their associated genomic characteristics (Foundation Medicine, Inc [FMI]). We moreover report the disease course and treatment response of an index patient with ROS1-rearranged metastatic CRC. ROS1 genomic rearrangements were identified in 34 (0.08%) CRC samples. GOPC-ROS1 was the most common ROS1 fusion identified (11 samples), followed by TTC28-ROS1 (3 samples). Four novel 5' gene partners of ROS1 were identified (MCM9, SRPK1, EPHA6, P4HA1). Contrary to previous reports on fusion-positive CRC, ROS1-rearrangements were found exclusively in microsatellite stable (MSS) CRCs. KRAS mutations were significantly less abundant in ROS1-rearranged vs ROS1 wild type cases. The index patient presented with chemotherapy-refractory metastatic right-sided colon cancer harboring GOPC-ROS1. Molecularly targeted treatment with crizotinib induced a rapid and sustained partial response. After 15 months on crizotinib disseminated tumor progression occurred and KRAS Q61H emerged in tissue and liquid biopsies. ROS1 rearrangements define a small, yet therapeutically actionable molecular subgroup of MSS CRC. In summary, the high prevalence of GOPC-ROS1 and noncanonical ROS1 fusions pose diagnostic challenges. We advocate NGS-based comprehensive molecular profiling of MSS CRCs that are wild type for RAS and BRAF and patient enrollment in precision trials.

| S-EPMC9804412 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data