Página 1 dos resultados de 88 itens digitais encontrados em 0.007 segundos

Use of Group 4 Bis(sulfonamido) Complexes in the Intramolecular Hydroamination of Alkynes and Allenes

Ackermann, Lutz; Bergman*, Robert G.; Loy, Rebecca N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/10/2003 Português
Relevância na Pesquisa
27.76%
Titanium tetrakis(amido) complexes catalyze the intramolecular hydroamination of alkynes and allenes more efficiently than Cp-based species. We report here that electron-withdrawing and sterically demanding bis(sulfonamido) ligands lead to enhanced catalytic activity. Zirconium analogues have also been prepared, and the tosyl-substituted complex 20 has been structurally characterized. As in the titanium series, bis(sulfonamido) zirconium catalysts are more efficient in the intramolecular hydroamination of allenes than bis(cyclopentadienyl) complex Cp2ZrMe2 (23). Furthermore, these compounds transform 1,3-disubstituted aminoallenes with high stereoselectivity to the Z-allylamines and allow the hydroamination of a trisubstituted allene. Titanium bis(sulfonamido) imido complex 27 was synthesized. It converts aminoallene 10 to cylic imine 11 with a rate comparable to that of tetrakis(amide) 15, supporting the hypothesis of a catalytically active titanium imido intermediate.

Zirconium Bis(Amido) Catalysts for Asymmetric Intramolecular Alkene Hydroamination

Watson, Donald A.; Chiu, Melanie; Bergman, Robert G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/09/2006 Português
Relevância na Pesquisa
27.24%
In situ combination of diphosphinic amides and Zr(NMe2)4 results in the formation of chiral zirconium bis(amido) complexes. The complexes are competent catalysts for intramolecular asymmetric alkene hydroamintion, providing piperidines and pyrrolidines in up to 80% ee and high yield. This system utilizes an inexpensive zirconium precatalyst and readily prepared ligands and is the first asymmetric alkene hydroamination catalyst based upon a neutral zirconium bis(amido) complex.

Catalytic intermolecular hydroamination of vinyl ethers

Pahadi, Nirmal K.; Tunge, Jon A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/12/2009 Português
Relevância na Pesquisa
27.56%
This manuscript details the development of a palladium-catalyzed hydroamination of vinyl ethers. It is proposed that palladium catalyzes the hydroamination via Bronsted base catalysis, where palladium is protonated by the relatively acidic sulfonamide to generate a palladium hydride as well as the active anionic sulfonamide nucleophile. Thus, this process is distinct from known palladium-catalyzed hydroaminations of styrene derivatives that utilize less acidic amines.

Platinum(II)-Catalyzed Intermolecular Hydroamination of Monosubstituted Allenes with Secondary Alkylamines†

Toups, Kristina L.; Widenhoefer, Ross A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.24%
A 1:1 mixture of (dppf)PtCl2 and AgOTf (5 mol %) catalyzed the intermolecular hydroamination of monosubstituted allenes with secondary alkylamines at 80 °C to form allylic amines in good yield with selective formation of the E-diastereomer.

Mechanistic Study of Gold(I)-Catalyzed Intermolecular Hydroamination of Allenes

Wang, Z. Jane.; Benitez, Diego; Tkatchouk, Ekaterina; Goddard, William A.; Toste, F. Dean
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 22/09/2010 Português
Relevância na Pesquisa
27.24%
The intermolecular hydroamination of allenes occurs readily with hydrazide nucleophiles, in the presence of 3–12% Ph3PAuNTf2. Mechanistic studies have been conducted to establish the resting state of the gold catalyst, the kinetic order of the reaction, the effect of ligand electronics on the overall rate, and the reversibility of the last steps in the catalytic cycle. We have found the overall reaction to be first order in gold and allene and zero order in nucleophile. Our studies suggest that the rate-limiting transition state for the reaction does not involve the nucleophile and that the active catalyst is monomeric in gold(I). Computational studies support an “outersphere” mechanism and predicts that a two-step, no intermediate mechanism may be operative. In accord with this mechanistic proposal, the reaction can be accelerated with the use of more electron deficient phosphine ligands on the gold(I) catalyst.

Intramolecular Hydroamination of Unbiased and Functionalized Primary Aminoalkenes Catalyzed by a Rhodium Aminophosphine Complex

Julian, Lisa D.; Hartwig, John F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 06/10/2010 Português
Relevância na Pesquisa
27.56%
We report a rhodium catalyst that exhibits high reactivity for the hydroamination of primary aminoalkenes that are unbiased toward cyclization and that possess functional groups that would not be tolerated in hydroaminations catalyzed by more electrophilic systems. This catalyst contains an unusual diaminophosphine ligand that binds to rhodium in a κ3-P,O,P mode. The reactions catalyzed by this complex typically proceed at mild temperatures (room temperature to 70 °C), occur with primary aminoalkenes lacking substituents on the alkyl chain that bias the system toward cyclization, occur with primary aminoalkenes containing chloride, ester, ether, enolizable ketone, nitrile, and unprotected alcohol functionality, and occur with primary aminoalkenes containing internal olefins. Mechanistic data imply that these reactions occur with a turnover-limiting step that is different from that of reactions catalyzed by late transition metal complexes of Pd, Pt, and Ir. This change in the turnover-limiting step and resulting high activity of the catalyst stem from favorable relative rates for protonolysis of the M-C bond to release the hydroamination product vs reversion of the aminoalkyl intermediate to regenerate the acyclic precursor. Probes for the origin of the reactivity of the rhodium complex of L1 imply that the aminophosphine groups lead to these favorable rates by effects beyond steric demands and simple electron donation to the metal center.

Gold(I)-Catalyzed Intermolecular Hydroamination of Allenes with Arylamines

Duncan, Alethea N.; Widenhoefer, Ross A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/2010 Português
Relevância na Pesquisa
27.24%
A mixture of (3)AuCl [3 = P(t-Bu)2o-biphenyl] and AgOTf catalyzes the intermolecular hydroamination of monosubstituted and 1,1- and 1,3-disubstituted allenes with primary and secondary arylamines.

Gold(I)-Catalyzed Intramolecular Hydroamination of N-Allylic,N′-Aryl Ureas to form Imidazolidin-2-ones

Li, Hao; Song, Feijie; Widenhoefer, Ross A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 18/04/2011 Português
Relevância na Pesquisa
27.56%
Treatment of N-allylic,N′-aryl ureas with a catalytic 1:1 mixture of di-tert-butyl-o-biphenylphoshphine gold(I) chloride and silver hexafluorophosphate (1 mol %) in chloroform at room temperature led to 5-exo hydroamination to form the corresponding imidazolidin-2-ones in excellent yield. In the case of N-allylic ureas that possessed an allylic alkyl, benzyloxymethyl, or acetoxymethyl substituent, gold(I)-catalyzed 5-exo hydroamination leads to formation of the corresponding trans-3,4-disubstituted imidazolidin-2-ones in excellent yield with ≥50:1 diastereoselectivity.

Anti-Markovnikov Hydroamination of Alkenes Catalyzed by an Organic Photoredox System

Nguyen, Tien M.; Nicewicz, David A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.56%
Herein we report a metal-free method for the direct anti-Markovnikov hydroamination of unsaturated amines. Irradiation of the amine substrates with visible light in the presence of catalytic quantities of easily synthesized 9-mesityl-10-methylacridinium tetrafluoroborate and thiophenol as a hydrogen atom donor furnished the nitrogen containing heterocycles with complete regio-control. Two examples of in termolecular anti-Markovnikov alkene hydroamination are also disclosed.

Formal Anti-Markovnikov Hydroamination of Terminal Olefins†

Bronner, Sarah M.; Grubbs, Robert H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2014 Português
Relevância na Pesquisa
27.76%
A new strategy to access linear amines from terminal olefin precursors is reported. This two-step, one-pot hydroamination methodology employs sequential oxidation and reduction catalytic cycles. The formal hydroamination transformation proceeds with excellent regioselectivity, and only the anti-Markovnikov product is observed. Up to 70% yield can be obtained from styrenes or aliphatic olefins and either primary or secondary aromatic amines. Additionally, the scope is broad with respect to the olefin and accommodates a variety of functionalities; we demonstrate that amines with removable aryl protecting groups may be utilized to allow access to a more diverse array of hydroamination adducts.

Enantio- and Regioselective CuH-Catalyzed Hydroamination of Alkenes

Zhu, Shaolin; Niljianskul, Nootaree; Buchwald, Stephen L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.56%
A highly enantio- and regioselective copper-catalyzed hydroamination reaction of alkenes has been developed using diethoxy(methyl)silane (DEMS) and esters of hydroxylamines. The process tolerates a wide variety of substituted styrenes, including trans-, cis-, and β,β-disubstituted styrenes to yield α–branched amines. In addition, aliphatic alkenes coupled to generate exclusively the anti-Markovnikov hydroamination products.

Enantioselective Synthesis of α-Aminosilanes by Copper-Catalyzed Hydroamination of Vinylsilanes**

Niljianskul, Nootaree; Zhu, Shaolin; Buchwald, Stephen L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.56%
The synthesis of α-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEG-PHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhydroxylamines as the electrophilic nitrogen source. This hydroamination reaction is compatible with differentially substituted vinylsilanes, thus providing access to amino acid mimics and other valuable chiral organosilicon compounds.

I. Engaging Cationic Intermediates in Asymmetric Catalysis: Enantioselective Reactions of Carbenium Ions and N,N-Dialkyliminium Ions II. Enantioselective Catalysis of the Cope-Type Hydroamination by H-Bond Donors

Brown, Adam Ross
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
Português
Relevância na Pesquisa
37.56%
The research described here explores the ability of dual H-bond donor catalysts to induce asymmetry in a variety of synthetically useful transformations that proceed via diverse reactive intermediates. In Chapters 1-3, we investigate ureas and thioureas as anion-binding catalysts for asymmetric reactions that proceeed via cationic intermediates with little precedent as electrophiles in asymmetric catalysis. Chapter 4 details our application of H-bond donor catalysis to the Cope-type hydroamination. Chapter 1 describes the development of an asymmetric aldehyde alkylation catalyzed by a bifunctional primary aminothiourea. A variety of 2-aryl propionaldehydes are alkylated with benzhydryl bromides in moderate to good yields and good enantioselectivities. Catalyst structure-activity relationship studies of the alkylation pointed towards electrophile activation by the dual H-bond donor moiety. Experiments aimed at gaining a better understanding of the electophile activation mode and characterizing the activated electrophilic intermediate in the alkylation reaction are described in Chapter 2. The development of an enantioselective cyanide addition to N,N-dialkyliminium intermediates is the subject of Chapter 3. A variety of strategies for accessing N...

Complexes pinceurs de cobalt et de nickel : synthèse, caratérisation, réactivité

Lefèvre, Xavier
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
Português
Relevância na Pesquisa
27.56%
Plusieurs nouveaux complexes pinceurs de cobalt et de nickel ont été préparés avec le ligand pinceur de type POCOP : 2,6-(i-Pr2PO)2C6H4. Dans le cas du cobalt, une nouvelle voie de synthèse a été développée. Contrairement au cas du nickel, il s’agit ici de cobalt au degré d’oxydation +III. Les composés obtenus sont paramagnétiques. En outre, le dérivé bromé est instable à la lumière et se décompose en perdant un brome pour former le complexe pinceur de Co(II). La réactivité de ces complexes a été étudiée. Pour ce qui est du nickel, la catalyse de l’hydroamination a été élargie aux dérivés de l’acrylonitrile et aux amines aromatiques. En outre, la réaction d’hydroaryloxylation a été étudiée dans les mêmes conditions. Enfin, avec le 4-cyanostyrène et le cinnamonitrile, la formation d’amidines a été observée. Un complexe pinceur portant cette amidine a été isolé. Enfin, le cation réagit avec des anions fortement coordonnants tels le cyanure ou l’isocyanate. En outre, l’anion triflate peut être déplacé par l’eau, l’acrylonitrile et ses dérivés. Enfin, une réactivité particulière a été observée avec la morpholine, l’acétone et un mélange 1:1 aniline/triéthylamine.; A large variety of new POCOP pincer type complexes of cobalt and nickel have been prepared. All those complexes are based on the following POCOP pincer type ligand: 2...

Chemoselective hydroamination of vinyl arenes catalyzed by an NHC-amidate-alkoxide Pd(II) complex and p-TsOH

Giles, Richard; O'Neill, Justin; Lee, Joo Ho; Chiu, Michael K.; Jung, Kyung Woon
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.56%
The hydroamination of various substituted vinyl arenes with benzenesulfonamide was explored using an NHC-amidate-alkoxide palladium catalyst in conjunction with p-TsOH. Utilizing halide-substituted and electron-rich vinyl arenes, this methodology selectively furnished the cross-coupled hydroamination products in moderate to excellent yields in a Markovnikov fashion while greatly reducing undesired acid-catalyzed homocoupling of the vinyl arenes. Electron-rich vinyl arenes typically required milder conditions than electron-poor ones. While most effective for para-substituted substrates, the catalyst system also furnished the desired products from ortho- and meta-substituted vinyl arenes with high chemoselectivities.

New half-sandwich alkyl, aryl, aryloxide, and propargyloxide titanium(iv) complexes containing a cyclopentadienyl ligand with a pendant ether substituent: behavior and influence in the hydroamination of alkynes of the ether group

Esteruelas, Miguel A.; López, Ana M.; Mateo, A. Concepción; Oñate, Enrique
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 13824 bytes; application/vnd.ms-excel
Português
Relevância na Pesquisa
27.56%
13 pages, 6 figures, 6 tables.; The complex CpOTiCl3 (1; CpO = C5H4CH2CH2OCH3) reacts with 1.0, 2.0, and 3.0 equiv of MeMgCl to give CpOTiMeCl2 (2), CpOTiMe2Cl (3), and CpOTiMe3 (4). In the solid state, the ether group of the pendant substituent of the cyclopentadienyl ligand is coordinated to the metal center (d(Ti−O) = 2.3373(18) Å in 2 and 2.2818(10) Å in 3) disposed transoid to a methyl ligand. In solution the O-donor substituent is involved in a coordination−dissociation equilibrium (ΔH° = 3.0 ± 0.7 kcal mol-1 and ΔS° = 12 ± 4 cal mol-1 K-1 for 2, ΔH° = 4.3 ± 0.1 kcal mol-1 and ΔS° = 17.2 ± 0.1 cal mol-1 K-1 for 3, and ΔH° = 2.3 ± 0.1 kcal mol-1 and ΔS° = 11.9 ± 0.3 cal mol-1 K-1 for 4). The reactions of 1 with 3.0 equiv of PhCH2MgCl, PhMgCl, and (p-tolyl)MgBr lead to CpOTiR3 (R = PhCH2 (5), Ph (6), p-tolyl (7)) containing a free pendant ether group. The X-ray structure of 6 shows a β-agostic Ti−H interaction between the metal center and a phenyl group (Ti−Cα−Cβ = 139.3(3) and 105.3(2)°). Complex 1 reacts with 1.0 equiv of Li(O-2,6-tBu2-4-MeC6H2) to give the six-coordinate aryloxide derivative CpOTi(O-2,6-tBu2-4-MeC6H2)Cl2 (8), which has been also characterized by X-ray diffraction analysis. The structure suggests a significant multiple bond character for the Ti−aryloxide bond (Ti−O−C = 151.31(14)°). The addition of 1.0 and 2.0 equiv of MeMgCl to 8 affords CpOTiMe(O-2...

Formal anti-Markovnikov hydroamination of terminal olefins

Bronner, Sarah M.; Grubbs, Robert H.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 19/09/2013 Português
Relevância na Pesquisa
27.76%
A new strategy to access linear amines from terminal olefin precursors is reported. This two-step, one-pot hydroamination methodology employs sequential oxidation and reduction catalytic cycles. The formal hydroamination transformation proceeds with excellent regioselectivity, and only the anti-Markovnikov product is observed. Up to 70% yield can be obtained from styrenes or aliphatic olefins and either primary or secondary aromatic amines. Additionally, the scope is broad with respect to the olefin and accommodates a variety of functionalities; we demonstrate that amines with removable aryl protecting groups may be utilized to allow access to a more diverse array of hydroamination adducts.

Gold(I)-Catalyzed Enantioselective Hydroamination of Unactivated Alkenes

Lee, seong du
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2012 Português
Relevância na Pesquisa
38.2%

Numerous methodologies for efficient formation of carbon-nitrogen bonds have been developed over the decades due to the widespread importance of nitrogen containing compounds in pharmaceuticals and bulk commercial chemicals. Among many methods, hydroamination, especially, has attracted enormous attention because of its atom-economical characteristic to synthesize amine moieties. As a result, numerous publications have been reported relating the hydroamination reaction using various metal catalysts. However, the hydroamination of unactivated alkenes still remains a challenge task because of the low reactivity of the CC double bond. Recent development of superior gold(I) catalysis in many organic transformations stimulated us to develop efficient gold(I)-catalyzed methods for enantioselective intra- and intermolecular hydroamination of unactivated alkenes.

A gold(I)-catalyzed system for enantioselective intramolecular hydroamination of unactivated alkenes has been developed. For the effective gold(I)-catalyzed method, various gold(I)-catalysts have been synthesized and tested. Among the catalysts, bis(gold) complexes containing an axially chiral bis(phosphine) ligand catalyze the enantioselective intramolecular hydroamination of unactivated alkenes with carboxamide derivatives...

Gold(I)-Catalyzed Hydrofunctionilzations of Allenes with Nitrogen and Oxygen Nucleophiles

Duncan, Alethea
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2011 Português
Relevância na Pesquisa
28.06%

The importance of nitrogen-containing compounds in human life has drawn us to focus on the preparation of amine derivatives, combined with the limitations associated with traditional methods for the formation of C-N bonds has prompted us to develop new and efficient syntheses, of amine and ether derivatives and explore the mechanisms of the gold(I)-catalyzed reactions.

A mixture of AuCl[P(t-Bu)2o-biphenyl] (5 mol %) and AgOTf (5 mol %) served as an effective catalyst for the intermolecular hydroamination of allenes with arylamines to form N-prenylaniline and N,N-diprenylaniline derivatives. This gold(I)-catalyzed protocol was effective for the formation of arylamines at non-forcing conditions with wide substrate scope in both allene and aniline, in high yields with good regioselectivity diastereoselectivity.

The mechanism of the gold(I)-catalyzed hydroalkoxylation and hydroamination of alcohols and carbamates with allenes, catalyzed by AuIPrCl (IPr= 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgOTf was investigated. The experimental rate laws for both reactions indicate first-order behavior in nucleophile and catalyst and zero-order behavior in catalyst. We propose an outer-sphere mechanism with turnover limiting protonolysis for the gold(I)-catalyzed hydrofunctionalization of allenes with alcohols or carbamates based on kinetic isotope effect...

Gold(I) and Platinum(II)-Catalyzed Hydrofunctionalization of Allenes and Alkenes with Carbon and Nitrogen Nucleophiles

Butler, Kristina LeAnne
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2012 Português
Relevância na Pesquisa
27.89%

The wide-spread occurrence of biologically active nitrogen-containing heterocycles and allylic amines inspired us to develop atom-economical methods for their syntheses.

A cationic gold(I) N-heterocyclic carbene complex catalyzed the intermolecular hydroarylation of allenes with indoles to form (E)-allylic indoles in modest to good yield at room temperature. The protocol was effective for monosubstituted, 1,3-disubstituted, and tetrasubstituted allenes and various indoles.

Platinum(II) bis(phosphine) complexes catalyzed the intermolecular hydroamination of monosubstituted allenes with secondary alkylamines in good yield with selective formation of (E)-allylic amines. The scope of the protocol included aryl and alkyl monosubstituted allenes as well as a variety of both cyclic and acyclic secondary alkylamines.

The scope of gold(I)-catalyzed intermolecular hydroamination of 1-alkenes with 1-methyl-2-imidazolidinone was expanded to include additional 1-alkenes functionalized with carboxylic acid derivatives. However, a nucleophile screen failed to identify nucleophiles other than cyclic ureas and 2-oxazolidinone that efficiently undergo hydroamination with 1-alkenes. Various carbamates...