Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Concerning the potential reversibility of carbometalation in alkoxide-directed Ti(Oi-Pr)4-mediated reductive cross-coupling of homoallylic alcohols with aromatic imines.

ABSTRACT: In an attempt to understand the nature of selectivity in Ti-mediated reductive cross-coupling between homoallylic alcohols and imines, we investigated whether thermodynamic equilibration of the presumed organometallic intermediate plays a role in selectivity. No evidence could be found for olefin exchange in preformed azatitanacyclopentanes--an observation that is consistent with a model based on kinetically controlled selective carbometalation.

SUBMITTER: Takahashi M

PROVIDER: S-EPMC3023109 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Concerning the potential reversibility of carbometalation in alkoxide-directed Ti(Oi-Pr)4-mediated reductive cross-coupling of homoallylic alcohols with aromatic imines.

Takahashi Masayuki M Micalizio Glenn C GC

Chemical communications (Cambridge, England) 20100408 19

In an attempt to understand the nature of selectivity in Ti-mediated reductive cross-coupling between homoallylic alcohols and imines, we investigated whether thermodynamic equilibration of the presumed organometallic intermediate plays a role in selectivity. No evidence could be found for olefin exchange in preformed azatitanacyclopentanes--an observation that is consistent with a model based on kinetically controlled selective carbometalation. ...[more]

PMID: 20379585

Similar Datasets

Preparation of stereodefined homoallylic amines from the reductive cross-coupling of allylic alcohols with imines.

Project description:Regio-, diastereo-, and enantioselective coupling reactions between imines and allylic alcohols have been developed. These coupling reactions deliver complex homoallylic amine products through a convergent C-C bond forming process that does not proceed through intermediate allylic organometallic reagents. In general, convergent coupling, by exposure of an allylic alkoxide to a preformed Ti-imine complex, occurs with allylic transposition in a predictable and stereocontrolled manner. While simple diastereoselection in these reactions is high, delivering anti-products with ?20:1 selectivity, the organometallic transformation described is compatible with a diverse range of functionality and substrates (including aliphatic and aromatic imines, allylic silanes, trisubstituted alkenes, vinyl- and aryl halides, trifluoromethyl groups, thioethers, and aromatic heterocycles). Alkene geometry of the products is a complex function of the allylic alcohol structure and is consistent with a mechanistic proposal based on syn-carbometalation followed by syn-elimination by way of a boat-like transition state geometry. Single asymmetric coupling reactions provide a means to translate the stereochemical information of the allylic alcohol to the homoallylic amine or to control diastereoselection in the coupling reactions of achiral allylic alcohols with chiral imines. Double asymmetric coupling reactions are also described that afford a unique means to control stereoselection in these complex convergent coupling processes. Finally, empirical models are proposed that are consistent with the observed stereochemical course of these coupling reactions en route to chiral homoallylic amines possessing di- or trisubstituted alkenes and anti- or syn- relative stereochemistry at the allylic and homoallylic positions.

| S-EPMC2993781 | biostudies-literature

Aliphatic imines in titanium-mediated reductive cross-coupling: unique reactivity of Ti(O-i-Pr)4/n-BuLi.

Project description:A procedure for the coupling of aliphatic imines with allylic and allenic alkoxides is described. The success of these studies was enabled by a unique reactivity profile of Ti(IV) isopropoxide/n-BuLi compared to well-known Ti(IV) isopropoxide/RMgX systems.

| S-EPMC2818175 | biostudies-literature

Polyketide assembly by alkene-alkyne reductive cross-coupling: spiroketals through the union of homoallylic alcohols.

Project description:A reaction sequence composed of regioselective formal hydroalkynylation, reductive ene-yne cross-coupling, and oxidative cyclization has been developed to prepare stereochemically dense spiroketals. Overall, the chemistry defines a three-component coupling process for the union of two homoallylic alcohol-based substrates with trimethylsilylacetylene.

| S-EPMC2892691 | biostudies-literature

Stereocontrolled synthesis of spiroketals via Ti(Oi-Pr)4-mediated kinetic spirocyclization of glycal epoxides with retention of configuration.

Project description:A Ti(Oi-Pr)4-mediated kinetic spiroketalization reaction has been developed for the stereocontrolled target- and diversity-oriented synthesis of spiroketals. In contrast to most existing methods for spiroketal synthesis, this reaction does not rely upon thermodynamic control over the stereochemical configuration at the anomeric carbon. Stereochemically diverse glycals are first alkylated at the C1-position to introduce a hydroxyl-bearing side chain, then epoxidized stereoselectively. Treatment with Ti(Oi-Pr)4 leads to an unusual kinetic epoxide-opening spirocyclization (spirocycloisomerization) with retention of configuration at the anomeric carbon. The reaction is proposed to proceed via a chelation-controlled mechanism and has been used to form five-, six-, and seven-membered rings with stereochemically diverse substituents. This approach may also be useful for the related intermolecular beta-mannosidation reaction. This Ti(Oi-Pr)4-mediated spirocyclization is stereochemically complementary to our previously reported MeOH-induced spirocyclization, which proceeds with inversion of configuration, and together, these reactions provide comprehensive access to systematically stereochemically diversified spiroketals.

| S-EPMC2553756 | biostudies-literature

Ti(Oi-Pr)<sub>4</sub>-promoted photoenolization Diels-Alder reaction to construct polycyclic rings and its synthetic applications.

Project description:Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis. These structures can be found in a wide range of polycyclic natural products and drug molecules. Here we report a Ti(Oi-Pr)4-promoted photoenolization/Diels-Alder (PEDA) reaction to construct hydroanthracenol and related polycyclic rings bearing all-carbon quaternary centers. This photolysis proceeds under mild conditions and generates a variety of photo-cycloaddition products in good reaction efficiency and stereoselectivity (48 examples), and has been successfully used in the construction of core skeleton of oncocalyxones, tetracycline and pleurotin. It also provides a reliable method for the late-stage modification of natural products bearing enone groups, such as steroids. The total synthesis of oncocalyxone B was successfully achieved using this PEDA approach.Anthracenols with multiple chiral centres are common motifs in natural products. Here, the authors show a highly stereoselective photoenolization/Diels-Alder methodology involving a key Lewis acid reagent enabling the efficient construction of a family of anthracenol derivatives with quaternary centers.

| S-EPMC5607006 | biostudies-literature

Catalytic enantioselective epoxidation of tertiary allylic and homoallylic alcohols.

Project description:An efficient and versatile method for the enantioselective epoxidation of both tertiary allylic and homoallylic alcohols catalyzed by Hf(IV)-bishydroxamic acid (BHA) complexes is described. Asymmetric epoxidation, kinetic resolution, and desymmetrization have been developed, demonstrating the flexible nature of the Hf(IV)-BHA system. This is the first report in which these substrates were obtained with enantioselectivities of up to 99%.

| S-EPMC3625140 | biostudies-literature

A multicomponent approach for the preparation of homoallylic alcohols.

Project description:Here we report the in situ generation of transient allylic boronic species, by reacting TMSCHN2 and E-vinyl boronic acids, followed by their subsequent trapping with aldehydes as electrophiles to yield homoallylic alcohols. This metal-free reaction was initially discovered by the use of a flow chemistry approach to generate a variety of homoallylic alcohols in a straightforward fashion and then transferred to a batch protocol.

| S-EPMC5134730 | biostudies-literature

Iodine-catalyzed prins cyclization of homoallylic alcohols and aldehydes.

Project description:The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. Anhydrous conditions and inert atmosphere are not required. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol and 21 aldehydes (aliphatic and aromatic) in CH?Cl? in the presence of 5 mol % of iodine gave 1,4,5,6-tetrahydro-2H-benzo[f]isochromenes in 54%-86% yield. Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary) led to dihydropyrans in 52%-91% yield. The acyclic homoallylic alcohols gave 4-iodo-tetrahydropyran in 29%-41% yield in the presence of 50 mol % of iodine. This type of substrate is the main limitation of the methodology. The relative configuration of the products was assigned by NMR and X-ray analysis. The mechanism and the ratio of the products are discussed, based on DFT calculations.

| S-EPMC6269844 | biostudies-other

Nickel-Catalyzed Reductive Alkylation of Heteroaryl Imines.

Project description:The preparation of heterobenzylic amines by a Ni-catalyzed reductive cross-coupling between heteroaryl imines and C(sp3 ) electrophiles is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and exhibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent Ni center. The resulting bis(2-imino)heterocycle⋅Ni complexes can engage in alkylation reactions with a variety of C(sp3 ) electrophiles, giving heterobenzylic amine products in good yields.

| S-EPMC9474666 | biostudies-literature

Vanadium-catalyzed addition of propargyl alcohols and imines.

Project description:A Mannich-type addition of propargylic alcohols and N-methoxycarbonylimines has been achieved by using a vanadium catalyst. The reactivity of the vanadium catalyst could be modulated by modifying the silanol ligands to avoid the background reaction. The strategy described herein provides an atom-economical access to beta-aryl-substituted Z-enones with an allylic amino functional group, which are not readily accessible with other methods.

| S-EPMC2529155 | 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