Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Origins of 1,6-stereoinduction in torquoselective 6? electrocyclizations.

ABSTRACT: A novel stereoselective electrocyclization developed for the total synthesis of reserpine has been explored by both experiment and theory. A stereocenter six atoms away from the newly forming chiral center is responsible for the diastereoselectivity of the ring closure. This stereogenic center, lying at the junction of two six-membered rings, defines the conformation of the substrates' fused ring skeleton that ultimately distinguishes between the two allowed, disrotatory triene geometries at the transition state. The presence of allylic strain in the disfavored transition state results in a torquoselective ring closure (dr up to 15.7:1).

SUBMITTER: Patel A

PROVIDER: S-EPMC3632451 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Origins of 1,6-stereoinduction in torquoselective 6π electrocyclizations.

Patel Ashay A Barcan Gregg A GA Kwon Ohyun O Houk K N KN

Journal of the American Chemical Society 20130318 12

A novel stereoselective electrocyclization developed for the total synthesis of reserpine has been explored by both experiment and theory. A stereocenter six atoms away from the newly forming chiral center is responsible for the diastereoselectivity of the ring closure. This stereogenic center, lying at the junction of two six-membered rings, defines the conformation of the substrates' fused ring skeleton that ultimately distinguishes between the two allowed, disrotatory triene geometries at the ...[more]

PMID: 23448287

Similar Datasets

A torquoselective 6? electrocyclization approach to reserpine alkaloids.

Project description:A highly torquoselective thermal triene 6? electrocyclization controls the relative stereochemistry between the C3 and C18 stereocenters of the dodecahydroindolo[2,3-a]benzo[g]quinolizine skeleton of reserpine-type alkaloids. Employing a tandem cross-coupling/electrocyclization protocol allowed us to form the requisite triene and ensure its subsequent cyclization. A novel low-temperature dibromoketene acetal Claisen rearrangement established the requisite exocyclic dienylbromide precursor for the palladium-catalyzed cross-coupling reaction.

| S-EPMC3488149 | biostudies-literature

Catalytic double stereoinduction in asymmetric allylic alkylation of oxindoles.

Project description:A highly regio-, diastereo-, and enantioselective allylic alkylation reaction of 3-monosubstituted oxindoles catalyzed by molybdenum is described. The reaction is affected by the electronic and steric variations of the nucleophile. The use of appropriate N-protecting group is particularly important for achieving high regio- and diastereoselectivity. Products from this reaction, containing vicinal quaternary-tertiary stereogenic centers, are valuable synthetic intermediates and should find utility in alkaloid synthesis.

| S-EPMC3488305 | biostudies-literature

Synthesis of ent-ketorfanol via a C-H alkenylation/torquoselective 6? electrocyclization cascade.

Project description:The asymmetric synthesis of ent-ketorfanol from simple and commercially available precursors is reported. A Rh(I) -catalyzed intramolecular C?H alkenylation/torquoselective 6??electrocyclization cascade provides a fused bicyclic 1,2-dihydropyridine as a key intermediate. Computational studies were performed to understand the high torquoselectivity of the key 6??electrocyclization. The computational results demonstrate that a conformational effect is responsible for the observed selectivity. The ketone functionality and final ring are introduced in a single step by a redox-neutral acid-catalyzed rearrangement of a vicinal diol to give the requisite carbonyl, followed by intramolecular Friedel-Crafts alkylation.

| S-EPMC4676713 | biostudies-literature

Torquoselective ring opening of fused cyclobutenamides: evidence for a cis,trans-cyclooctadienone intermediate.

Project description:Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3. Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

| S-EPMC4353010 | biostudies-literature

Beyond TME Origins

Project description:All patients with recurrent colorectal cancer in the pelvis are eligible. The original primary tumour staging scans and resected surgical specimen needs to be available. Patients’ recurrence will be staged using our proposed MRI classification. We will be assessing the original primary staging scans and histopathology to learn about risk factors for recurrence. We will record treatment for the recurrence, and patients will be followed up for three years.

| 2178413 | ecrin-mdr-crc

RNA-seq Mouse 2-cell 1,6-Hexanediol

Project description:The majority of our genome is composed of repeated DNA sequences, which assemble into heterochromatin, a highly compacted structure that constrains their mutational potential. How heterochromatin forms during development and how its structure is maintained is not fully understood. Here, we show that mouse heterochromatin phase separates after fertilization, during the earliest stages of mammalian embryogenesis. Using high resolution, quantitative imaging and molecular biology approaches we show that pericentromeric heterochromatin displays liquid-like properties at the 2-cell stage, but it transitions into a more solid-like or gel-like state at the 4-cell stage, when chromocenters mature and heterochromatin becomes silent. Disrupting the condensates results in altered transcript levels of pericentromeric heterochromatin, suggesting a functional role for phase separation in heterochromatin function. Thus, our work shows that mouse heterochromatin forms membrane-less compartments with biophysical properties that change during development and provides new insights into the self-organization of chromatin domains during mammalian embryogenesis.

2023-08-23 | GSE211872 | GEO

Chiral Photochemistry in a Confined Space: Torquoselective Photoelectrocyclization of Pyridones within an Achiral Hydrophobic Capsule.

Project description:Chiral induction during the photoelectrocyclization of pyridones included within octa acid (OA) capsule has been established. Chiral induction is brought about by a chiral auxiliary appended to the reactive pyridone moiety. Importantly, the same chiral auxiliary while ineffective in acetonitrile solution is found to be effective within the confined space of OA capsule. The diastereomeric excess of 92% obtained here is comparable only to that in solid state. OA capsule, we believe, provides restriction to the rotational motions of the reactant pyridone and chiral auxiliary and thus places the chiral auxiliary in a selective conformation with respect to the reactive pyridone part. A correlation between the position of the methyl group on the pyridone ring and diastereoselectivity was noted. Structures of the host-guest complexes were examined by (1)H NMR and the data was used to obtain preliminary information concerning the mechanism of chiral induction within the confined spaces of OA capsule.

| S-EPMC2964841 | biostudies-literature

Hexane-1,6-diammonium dinitrate.

Project description:The hexane-1,6-diammonium cation of the title compound, C(6)H(18)N(2) (2+)·2NO(3) (-), lies across a crystallographic inversion centre and shows significant deviation from planarity in the hydro-carbon chain. This is evident from the torsion angle of -64.0°(2) along the N-C-C-C bond and thse torsion angle of -67.1°(2) along the C-C-C-C bonds. An intricate three-dimensional hydrogen-bonding network exists in the crystal structure, with each H atom on the ammonium group exhibiting bifurcated inter-actions to the nitrate anion. Complex hydrogen-bonded ring and chain motifs are also evident, in particular a 26-membered ring with graph-set notation R(4) (4)(26) is observed.

| S-EPMC2977696 | biostudies-literature

An Asymmetric Vinylogous Michael Cascade of Silyl Glyoximide, Vinyl Grignard, and Nitroalkenes via Long Range Stereoinduction.

Project description:A diastereoselective auxiliary-mediated vinylation/[1,2]-Brook rearrangement/vinylogous Michael cascade of silyl glyoximide, vinylmagnesium bromide, and nitroalkenes is described. The reaction occurs with complete regio- and diastereocontrol in good yield. The diastereoselectivity is induced by a rare instance of 1,7-chirality transfer that is hypothesized to arise from a trans-multihetero-decalin transition state.

| S-EPMC4761320 | biostudies-literature

Glutathione-dependent dechlorination of 1,6-dichloro-1,6-dideoxyfructose.

Project description:The metabolism of 14C- and 36Cl-labelled 1,6-dichloro-1,6-dideoxyfructose (DCF) was studied in the isolated perfused rat liver system. Dechlorination of DCF occurred in the liver and erythrocytes and was GSH-dependent. The GSH conjugate formed was identified by 13C and 1H n.m.r. as the 6-chlorofructos-1-yl-SG conjugate. It is proposed that the GS- anion attacks the low steady-state concentration of the reactive keto form of DCF and that the conjugate formed cyclizes to the dominant beta-anomer. 6-Chlorofructos-1-yl-SG conjugate of hepatic origin is excreted into bile, whereas that produced in erythrocytes does not enter the liver.

| S-EPMC1138541 | biostudies-other

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

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