Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Synthetic studies and mechanistic insight in nickel-catalyzed [4+2+1] cycloadditions.

ABSTRACT: A new nickel-catalyzed procedure for the [4+2+1] cycloaddition of (trimethylsilyl)diazomethane with alkynes tethered to dienes has been developed. A broad range of unsaturated substrates participate in the sequence, and stereoselectivities are generally excellent. Stereochemical studies provided evidence for a mechanism that involves the [3,3] sigmatropic rearrangement of divinylcyclopropanes.

SUBMITTER: Ni Y

PROVIDER: S-EPMC2720272 | biostudies-literature | 2006 Mar

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Synthetic studies and mechanistic insight in nickel-catalyzed [4+2+1] cycloadditions.

Ni Yike Y Montgomery John J

Journal of the American Chemical Society 20060301 8

A new nickel-catalyzed procedure for the [4+2+1] cycloaddition of (trimethylsilyl)diazomethane with alkynes tethered to dienes has been developed. A broad range of unsaturated substrates participate in the sequence, and stereoselectivities are generally excellent. Stereochemical studies provided evidence for a mechanism that involves the [3,3] sigmatropic rearrangement of divinylcyclopropanes. ...[more]

PMID: 16492045

Similar Datasets

Photochemical Nickel-Catalyzed C-H Arylation: Synthetic Scope and Mechanistic Investigations.

Project description:An iridium photocatalyst and visible light facilitate a room temperature, nickel-catalyzed coupling of (hetero)aryl bromides with activated α-heterosubstituted or benzylic C(sp3)-H bonds. Mechanistic investigations on this unprecedented transformation have uncovered the possibility of an unexpected mechanism hypothesized to involve a Ni-Br homolysis event from an excited-state nickel complex. The resultant bromine radical is thought to abstract weak C(sp3)-H bonds to generate reactive alkyl radicals that can be engaged in Ni-catalyzed arylation. Evidence suggests that the iridium photocatalyst facilitates nickel excitation and bromine radical generation via triplet-triplet energy transfer.

| S-EPMC5054938 | biostudies-literature

Nickel-catalyzed cycloadditions of unsaturated hydrocarbons, aldehydes, and ketones.

Project description:The nickel-catalyzed cycloaddition of unsaturated hydrocarbons and carbonyls is reported. Diynes and enynes were used as coupling partners. Carbonyl substrates include both aldehdyes and ketones. Reactions of diynes and aldehydes afforded the [3,3] electrocyclic ring-opened tautomers, rather than pyrans, in high yields. The cycloaddition reaction of enynes and aldehydes afforded two distinct products. A new carbon-carbon bond is formed, prior to a competitive beta-hydrogen elimination of a nickel alkoxide, between the carbonyl carbon and either one of the carbons of the olefin or the alkyne. The steric hindrance of the enyne greatly affected the chemoselectivity of the cycloaddition of enynes and aldehydes. In some cases, dihydropyran was also formed. The scope of the cycloaddition reaction was expanded to include the coupling of enynes and ketones. No beta-hydrogen elimination was observed in cycloaddition reaction of enynes and ketones. Instead, C-O bond-forming reductive elimination occurred exclusively to afford dihydropyrans in excellent yields. In all cases, complete chemoselectivity was observed; only dihydropyrans where the carbonyl carbon forms a carbon-carbon bond with a carbon of the olefin, rather than of the alkyne, were observed. All cycloaddition reactions occur at room temperature and employ nickel catalysts bearing the hindered 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or its saturated analogue, 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazolin-2-ylidene (SIPr).

| S-EPMC4144363 | biostudies-literature

Nickel-Catalyzed Three-Component Cycloadditions of Enoates, Alkynes, and Aldehydes.

Project description:A method for the three-component cycloaddition of enoates, alkynes, and aldehydes has been developed. Building upon previous work by this group in which stoichiometrically generated metallacycles undergo alkylation, we report a catalytic, alkylative [3 + 2] cycloaddition. From simple starting materials, structurally complex cyclopentenones may be rapidly assembled. Computational investigation of the mechanism (ωB97X-D3/cc-pVTZ//ωB97X/6-31G(d)) identified three energetically feasible pathways. Based on the relative rates of ketene formation compared to isomerization to a seven-membered metallacycle, the most likely mechanism has been determined to occur "ketene-first", with carbocyclization prior to aldol addition. Deuterium labeling studies suggest that formation of the seven-membered metallacycle becomes possible when an α-substituted enoate is used. This observed change in selectivity is due to the increased difficulty of phenoxide elimination with the inclusion of additional steric bulk of the α-substituent. The net transformation results in a [3 + 2] cycloaddition accompanied by an alkylation of the enoate substituent.

| S-EPMC7167596 | biostudies-literature

Synthetic and mechanistic studies on Pd(0)-catalyzed diamination of conjugated dienes.

Project description:Various dienes and a triene can be regioselectively diaminated at the internal double bond with good yields and high diastereoselectivity using di-tert-butyldiaziridinone (5) as the nitrogen source and Pd(PPh(3))(4) (1-10 mol %) as the catalyst. Kinetic studies with (1)H NMR spectroscopy show that the diamination is first-order in total Pd catalyst and inverse first-order in PPh(3). For reactive dienes, such as 1-methoxybutadiene (6g) and alkyl 1,3-butadienes (6a, 6j), the diamination is first-order in di-tert-butyldiaziridinone (5) and zero-order in the olefin. For olefins with relatively low reactivity, such as (E)-1-phenylbutadiene (6b) and (3E,5E)-1,3,5-decatriene (6i), similar diamination rates were observed when 3.5 equiv of olefins were used. Pd(PPh(3))(2) is likely to be the active species for the insertion of Pd(0) into the N-N bond of di-tert-butyldiaziridinone (5) to form a four-membered Pd(II) complex (A), which can be detected by NMR spectroscopy. The olefin complex (B), formed from intermediate A via ligand exchange between the olefin substrate and the PPh(3), undergoes migratory insertion and reductive elimination to give the diamination product and regenerate the Pd(0) catalyst.

| S-EPMC2846102 | biostudies-literature

A mild, palladium-catalyzed method for the dehydrohalogenation of alkyl bromides: synthetic and mechanistic studies.

Project description:We have exploited a typically undesired elementary step in cross-coupling reactions, ?-hydride elimination, to accomplish palladium-catalyzed dehydrohalogenations of alkyl bromides to form terminal olefins. We have applied this method, which proceeds in excellent yield at room temperature in the presence of a variety of functional groups, to a formal total synthesis of (R)-mevalonolactone. Our mechanistic studies have established that the rate-determining step can vary with the structure of the alkyl bromide and, most significantly, that L(2)PdHBr (L = phosphine), an intermediate that is often invoked in palladium-catalyzed processes such as the Heck reaction, is not an intermediate in the active catalytic cycle.

| S-EPMC3432975 | biostudies-literature

Palladium-Catalyzed Intra- and Intermolecular C-H Arylation Using Mesylates: Synthetic Scope and Mechanistic Studies.

Project description:This paper describes the development of Pd-catalyzed inter- and intramolecular direct arylation using mesylates. Furthermore, a sequential mesylation/arylation protocol using phenols as substrates is described. These transformations are general with respect to the electronics of the C-H substrates and allow for the synthesis of diverse heterocyclic motifs in good yields. Both arenes and heteroarenes efficiently participate in these reactions. Preliminary mechanistic studies are presented for both inter- and intramolecular arylations.

| S-EPMC4105186 | biostudies-literature

Nickel-catalyzed Negishi arylations of propargylic bromides: a mechanistic investigation.

Project description:Although nickel-catalyzed stereoconvergent couplings of racemic alkyl electrophiles are emerging as a powerful tool in organic chemistry, to date there have been no systematic mechanistic studies of such processes. Herein, we examine the pathway for enantioselective Negishi arylations of secondary propargylic bromides, and we provide evidence for an unanticipated radical chain pathway wherein oxidative addition of the C-Br bond occurs through a bimetallic mechanism. In particular, we have crystallographically characterized a diamagnetic arylnickel(II) complex, [(i-Pr-pybox)Ni(II)Ph]BAr(F)4, and furnished support for [(i-Pr-pybox)Ni(II)Ph](+) being the predominant nickel-containing species formed under the catalyzed conditions as well as a key player in the cross-coupling mechanism. On the other hand, our observations do not require a role for an organonickel(I) intermediate (e.g., (i-Pr-pybox)Ni(I)Ph), which has previously been suggested to be an intermediate in nickel-catalyzed cross-couplings, oxidatively adding alkyl electrophiles through a monometallic pathway.

| S-EPMC4277758 | biostudies-literature

Mechanistic Investigation of the Nickel-Catalyzed Transfer Hydrocyanation of Alkynes.

Project description:The implementation of HCN-free transfer hydrocyanation reactions on laboratory scales has recently been achieved by using HCN donor reagents under nickel- and Lewis acid co-catalysis. More recently, malononitrile-based HCN donor reagents were shown to undergo the C(sp3)-CN bond activation by the nickel catalyst in the absence of Lewis acids. However, there is a lack of detailed mechanistic understanding of the challenging C(sp3)-CN bond cleavage step. In this work, in-depth kinetic and computational studies using alkynes as substrates were used to elucidate the overall reaction mechanism of this transfer hydrocyanation, with a particular focus on the activation of the C(sp3)-CN bond to generate the active H-Ni-CN transfer hydrocyanation catalyst. Comparisons of experimentally and computationally derived 13C kinetic isotope effect data support a direct oxidative addition mechanism of the nickel catalyst into the C(sp3)-CN bond facilitated by the coordination of the second nitrile group to the nickel catalyst.

| S-EPMC10476158 | biostudies-literature

Mechanistic insight into TRIP13-catalyzed Mad2 structural transition and spindle checkpoint silencing.

Project description:The spindle checkpoint maintains genomic stability and prevents aneuploidy. Unattached kinetochores convert the latent open conformer of the checkpoint protein Mad2 (O-Mad2) to the active closed conformer (C-Mad2), bound to Cdc20. C-Mad2-Cdc20 is incorporated into the mitotic checkpoint complex (MCC), which inhibits the anaphase-promoting complex/cyclosome (APC/C). The C-Mad2-binding protein p31comet and the ATPase TRIP13 promote MCC disassembly and checkpoint silencing. Here, using nuclear magnetic resonance (NMR) spectroscopy, we show that TRIP13 and p31comet catalyze the conversion of C-Mad2 to O-Mad2, without disrupting its stably folded core. We determine the crystal structure of human TRIP13, and identify functional TRIP13 residues that mediate p31comet-Mad2 binding and couple ATP hydrolysis to local unfolding of Mad2. TRIP13 and p31comet prevent APC/C inhibition by MCC components, but cannot reactivate APC/C already bound to MCC. Therefore, TRIP13-p31comet intercepts and disassembles free MCC not bound to APC/C through mediating the local unfolding of the Mad2 C-terminal region.

| S-EPMC5717197 | biostudies-other

Functionalized cyclopentenes through a tandem NHC-catalyzed dynamic kinetic resolution and ambient temperature decarboxylation: mechanistic insight and synthetic application.

Project description:An unusual room temperature β-lactone decarboxylation facilitated a five-step enantioselective formal synthesis of the cyclopentane core of an estrogen receptor β-agonist. A computational study probed the underlying factors facilitating unprecedented, rapid decarboxylation. Aryl substitution promotes faster reaction in the retro-[2+2] as a result of conjugative stabilization with the forming olefin. Additionally, the configuration of the α-ester in these fused β-lactones leads to differential decarboxylation rates.

| S-EPMC4312178 | 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