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1.
Angew Chem Int Ed Engl ; 59(20): 7648, 2020 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-32249993

RESUMO

Kilian Muñiz passed away unexpectedly on March 16th, 2020, at the age of only 49. Kilian was a leading figure in the field of catalytic (di-)amination reactions. He will be remembered as one of the finest, most passionate chemists, a dear colleague, and, most of all, as a close friend.

2.
Chemistry ; 2020 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-32236985

RESUMO

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold-silver clusters with ortho-metalated phosphines displaying 3c-2e Au-C-M bonds (M=Au/Ag). Hexagold clusters [Au6 L4 ](X)2 are obtained by reaction of (L-TMS)AuCl with AgX, whereas reaction with AgX and Ag2 O leads to gold-silver clusters [Au4 Ag2 L4 ](X)2 . Oxo-trigold(I) species [Au3 O]+ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au5 ], [Au4 Ag], and [Au12 Ag4 ] clusters were also obtained. Clusters containing PAu-Au-AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.

3.
Org Lett ; 2020 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-32243187

RESUMO

The photoredox-assisted gold-catalyzed arylative cyclization of 1,6-enynes with aryldiazonium salts gives rise to cyclization products with the opposite configuration at the alkene than that obtained by gold(I)-catalyzed alkoxycyclization. The reaction occurs under mild conditions and shows high functional group tolerance.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32196899

RESUMO

An Ir-catalyzed C(sp3 )-H alkynylation of aliphatic ketones, aldehydes, and alcohols was achieved by using the corresponding oxime derivatives and a IrIII catalyst. This general reaction is selective towards primary C(sp3 )-H bonds and can be used for the late-stage C-H alkynylation of complex molecules.

5.
Angew Chem Int Ed Engl ; 59(12): 4888-4891, 2020 03 16.
Artigo em Inglês | MEDLINE | ID: mdl-31912609

RESUMO

The gold(I)-catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)-1,4-disubstituted 1,3-butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user-friendly procedure. Reaction of acetylene with 1,5-dienes gives rise stereoselectively to tricyclo[5.1.0.02,4 ]octanes. This novel double cyclopropanation has been applied to the one step total synthesis of the natural product waitziacuminone from acetylene and geranyl acetone.

6.
Org Lett ; 21(22): 9262-9267, 2019 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-31661284

RESUMO

Decarboxylative Csp3-N coupling reactions have been developed through electrochemical oxidation of amino acids. The reaction proceeds via anodic oxidative decarboxylation of carboxylic acids to form stabilized carbocations, which are trapped by azoles or amides to construct C-N bonds. This method avoids the preactivation of carboxylic acids and the use of expensive transition-metals and external chemical oxidants.

7.
J Am Chem Soc ; 141(30): 11858-11863, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31290658

RESUMO

Chiral gold(I) catalysts have been designed based on a modified JohnPhos ligand with a distal C2-2,5-diarylpyrrolidine that creates a tight binding cavity. The C2-chiral element is close to where the C-C bond formation takes place in cyclizations of 1,6-enynes. These chiral mononuclear catalysts have been applied for the enantioselective 5-exo-dig and 6-endo-dig cyclization of different 1,6-enynes as well as in the first enantioselective total synthesis of three members of the carexane family of natural products. Opposite enantioselectivities have been achieved in seemingly analogous reactions of 1,6-enynes, which result from different chiral folding of the substrates based on attractive aryl-aryl interactions.

8.
Acc Chem Res ; 52(7): 1812-1823, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31264834

RESUMO

The quest for organic materials with improved optoelectronic properties has stimulated the development of new strategies for the preparation of polycyclic aromatic hydrocarbons. Within this context, transition metal catalysis offers unparalleled opportunities for the assembly of complex molecular architectures. The palladium-catalyzed direct C-H arylation provides straight access to biaryls without the need of prefunctionalization at the nucleophilic site, which is attractive from the perspective of the synthesis of polyarenes. Mechanistically, this reaction was found to be different from an electrophilic aromatic substitution, involving the abstraction of a proton by an external base in the key metalation step. Using readily available C27 truxene as the starting material, a concise synthetic route consisting of a threefold benzylation and subsequent palladium-catalyzed arylation led to C60 polyarenes, also referred to as "crushed fullerenes", which could be converted into C60 fullerene by laser-induced cyclodehydrogenation in the gas phase or by thermal cyclodehydrogenation on a platinum surface. A conceptually related strategy based on the use of a highly electrophilic gold(I) complex as the catalyst for the threefold intramolecular hydroarylation of truxene derivatives was applied for the synthesis of decacyclenes. Using gold(I) catalysis, we have also developed a variety of synthetically useful protocols for the cycloisomerization of readily available 1,n-enynes as well as for the addition for nucleophiles to these unsaturated substrates. In one of these transformations, 1,7-enynes bearing aryl-substituted alkynes undergo formal [4 + 2] cycloaddition reactions via gold(I)-catalyzed 6-exo-dig cyclization and intramolecular Friedel-Crafts-type reaction to form tricyclic compounds bearing a dihydronaphthalene core. A related transformation led to a general synthesis of hydroacenes, which are known to be stabilized precursors of the corresponding conjugated acenes with enhanced solubility. A wide variety of dihydrotetracenes featuring electron-donating and electron-withdrawing groups, as well as dihydropentacene and dihydrohexacene could be easily obtained. A simple variation of our synthetic route led to tetrahydro-derivatives of higher acenes with up to 11 linearly fused six-membered rings. The dehydrogenation of tetrahydroacenes on a metallic substrate using the tip of a scanning tunneling microscopy instrument or by thermal annealing enabled the preparation of the whole series of higher acenes from heptacene up to previously unknown undecacene, whose structure was confirmed by noncontact atomic force microscopy. This work provided a unique opportunity for the analysis of the evolution of the transport gap in the acene series on Au(111). Furthermore, heptacene was also generated by on-surface dehydrogenation on Ag(001) from tetrahydroheptacene and a dibrominated derivative.

9.
Sci Data ; 6(1): 15, 2019 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-30944327

RESUMO

This Data Descriptor announces the submission to public repositories of the monoterpene indole alkaloid database (MIADB), a cumulative collection of 172 tandem mass spectrometry (MS/MS) spectra from multiple research projects conducted in eight natural product chemistry laboratories since the 1960s. All data have been annotated and organized to promote reuse by the community. Being a unique collection of these complex natural products, these data can be used to guide the dereplication and targeting of new related monoterpene indole alkaloids within complex mixtures when applying computer-based approaches, such as molecular networking. Each spectrum has its own accession number from CCMSLIB00004679916 to CCMSLIB00004680087 on the GNPS. The MIADB is available for download from MetaboLights under the identifier: MTBLS142 ( https://www.ebi.ac.uk/metabolights/MTBLS142 ).

10.
Org Biomol Chem ; 17(17): 4216-4219, 2019 04 24.
Artigo em Inglês | MEDLINE | ID: mdl-30945718

RESUMO

A gold(i)-catalyzed cyclopropane-alkene metathesis has been demonstrated with two new families of cyclopropane derivatives of naphthalene and phenanthrene (benzo-fused norcaradienes). In this process, metal carbene units are transferred from a persistent cyclopropane to an alkene, upon release of naphthalene or phenanthrene, allowing the diastereoselective synthesis of a wide range of aryl and vinyl cyclopropanes.

11.
Chemistry ; 25(40): 9485-9490, 2019 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-31001873

RESUMO

A novel synthesis of indanes and dihydronaphtalenes based on the intramolecular insertion into C(sp3 )-H bonds of gold(I) carbenes generated by retro-Buchner reaction (decarbenation) has been developed. Deuterium-labeling and kinetic isotope effect experiments, DFT calculations, and generation of the proposed carbene intermediate from a well-characterized gold(I) carbenoid support the involvement of a three-center concerted mechanism for the C(sp3 )-H functionalization process.

12.
Angew Chem Int Ed Engl ; 58(12): 3957-3961, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30644625

RESUMO

Mesityl gold(I) carbenes lacking heteroatom stabilization or shielding ancillary ligands have been generated and spectroscopically characterized from chloro(mesityl)methylgold(I) carbenoids bearing JohnPhos-type ligands by chloride abstraction with GaCl3 . The aryl carbenes react with PPh3 and alkenes to give stable phosphonium ylides and cyclopropanes, respectively. Oxidation with pyridine N-oxide and intermolecular C-H insertion to cyclohexane have also been observed. In the absence of nucleophiles, a bimolecular reaction, similar to that observed for other metal carbenes, leads to a symmetrical alkene.

13.
Angew Chem Int Ed Engl ; 58(7): 2088-2092, 2019 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-30561881

RESUMO

Rhodium carbenes are key intermediates in a range of cycloadditions and insertion reactions. Herein, we report the first generation of donor RhII carbenes by decarbenation of 7-substituted 1,3,5-cycloheptatrienes. This discovery unlocks an improved retro-Buchner-cyclopropanation sequence, a Si-H insertion reaction for a broad-scope synthesis of allylsilanes, and a new method for the vinylogation of aldehydes. The last strategy led to the development of an iterative synthesis of E-polyenes, and to the total synthesis of navenones B and C.

14.
Org Lett ; 20(18): 5784-5788, 2018 09 21.
Artigo em Inglês | MEDLINE | ID: mdl-30198722

RESUMO

The first total synthesis of repraesentin F has been accomplished by a highly diastereoselective gold(I)-catalyzed cyclization cascade as the key step. This cycloisomerization/Prins-type tandem transformation enabled direct access to the atypical tricyclic carbon skeleton of the natural product with the required syn/ anti/ syn ring fusion. This synthetic effort also allowed reassignment of the relative configuration of repraesentin F and determination of its absolute configuration.

15.
Chem Commun (Camb) ; 54(73): 10260-10263, 2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-30152499

RESUMO

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.

16.
Chemistry ; 24(58): 15613-15621, 2018 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-30066978

RESUMO

The reaction of oxime-tethered 1,6-enynes with a cationic gold(I) catalyst demonstrates a great potential for the synthesis of a range of heterocycles in a diastereospecific fashion. The control of the configuration of the oxime and the alkene of the enyne moiety is the key to selectively obtain dihydro-1,2-oxazines, isoxazolines or dihydropyrrole-N-oxides as single diastereoisomers. As supported by DFT calculations, these cascade reactions proceed stepwise, by the intramolecular addition of the O or N atom of the oxime onto cyclopropyl gold(I) carbene intermediates. In this study, a rare [3,3]-sigmatropic rearrangement of nitrones is also observed.

17.
Org Lett ; 20(14): 4341-4345, 2018 07 20.
Artigo em Inglês | MEDLINE | ID: mdl-29975067

RESUMO

Through the design of a second generation of more reactive 7-substituted 1,3,5-cycloheptatrienes, a room-temperature gold(I)-catalyzed retro-Buchner-cyclopropanation sequence and the first zinc(II)-catalyzed version of this process, which uses inexpensive ZnBr2 as catalyst, have been developed. This led to a broad-scope cyclopropanation of both activated and unactivated alkenes, including late-stage derivatization of biologically relevant compounds, and to the total synthesis of (±)-lactobacillic acid.

18.
Angew Chem Int Ed Engl ; 57(33): 10500-10505, 2018 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-29791082

RESUMO

A unified approach to the synthesis of the series of higher acenes up to previously unreported undecacene has been developed through the on-surface dehydrogenation of partially saturated precursors. These molecules could be converted into the parent acenes by both atomic manipulation with the tip of a scanning tunneling and atomic force microscope (STM/AFM) as well as by on-surface annealing. The structure of the generated acenes has been visualized by high-resolution non-contact AFM imaging and the evolution of the transport gap with the increase of the number of fused benzene rings has been determined on the basis of scanning tunneling spectroscopy (STS) measurements.

19.
Organometallics ; 37(5): 781-786, 2018 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-29551852

RESUMO

Gold(I) acetylide and σ,π-digold(I) alkyne complexes derived from one prototypical 1,6-enyne and from 7-ethynyl-1,3,5-cycloheptatriene have been prepared and structurally characterized. Their possible role in gold(I)-catalyzed cycloisomerizations has been studied by experiment and by DFT calculations. Gold(I) acetylides are totally unproductive complexes in the absence of Brønsted acids. Similarly, no cyclizations were observed by heating σ,π-digold(I) alkyne digold(I) at least up to 130 °C. Theoretical studies provide a rationale for the much lower reactivity of digold species in reactions of enynes.

20.
ACS Catal ; 8(3): 2166-2172, 2018 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-29527402

RESUMO

We report the alkynylation of C(sp2)-H bonds with bromoalkynes (inverse-Sonogashira reaction) directed by synthetically useful ester, ketone, and ether groups under rhodium catalysis. Other less common directing groups such as amine, thioether, sulfoxide, sulfone, phenol ester, and carbamate are also suitable directing groups. Mechanistic studies indicate that the reaction proceeds by a turnover-limiting C-H activation step via an electrophilic-type substitution.

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