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ABSTRACT: We report the gold-catalyzed synthesis of highly functionalized iodofulvenes from iododialkynes under mild conditions. The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates. These intermediates can then undergo an unprecedented iodine/gold exchange. This new pathway for catalyst transfer in dual gold catalysis opens up the possibility of highly regioselective transformations directed by the gold in the organogold intermediates. The resulting products are well suited for further metal-mediated coupling reactions, allowing the synthesis of extended π-systems.
Chemistry 05/2013; · 5.93 Impact Factor
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ABSTRACT: When an ynamide meets a gold carbenoid: Highly electrophilic gold carbenoids available from propargylic esters by means of 1,2-acyloxy migration open up new reaction pathways for ynamide gold chemistry. In this way highly functionalized cyclopentadiene derivatives become accessible (see scheme; EWG=electron-withdrawing group).
Angewandte Chemie International Edition 04/2013; · 13.45 Impact Factor
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ABSTRACT: The β-H-elimination in the (iPr)AuEt complex and its microscopic reverse, the insertion of ethene into (iPr)AuH, were investigated in a combined experimental and computational study. Our DFT-D3 calculations predict free-energy barriers of 49.7 and 36.4 kcal mol for the elimination and insertion process, respectively, which permit an estimation of the rate constants for these reactions according to classical transition-state theory. The elimination/insertion pathway is found to involve a high-energy ethene hydride species and is not significantly affected by continuum solvent effects. The high barriers found in the theoretical study were then confirmed experimentally by measuring decomposition temperatures for several different (iPr)Au -alkyl complexes which, with a slow decomposition at 180 °C, are significantly higher than those of other transition-metal alkyl complexes. In addition, at the same temperature, the decomposition of (iPr)AuPh and (iPr)AuMe, both of which cannot undergo β-H-elimination, indicates that the pathway for the observed decomposition at 180 °C is not a β-H-elimination. According to the calculations, the latter should not occur at temperatures below 200 °C. The microscopic reverse of the β-H-elimination, the insertion of ethene into the (iPr)AuH could neither be observed at pressures up to 8 bar at RT nor at 1 bar at 80 °C. The same is true for the strain-activated norbornene.
Chemistry 03/2013; 19(12):3954-61. · 5.93 Impact Factor
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ABSTRACT: We report the successful synthesis of a series of ethynylated dioxadiazaacenes and investigate their properties. We developed a modular Cu-based catalytic procedure to build up [1,4]dioxino[2,3-b]pyrazine-motifs, starting from a only a few building blocks. TIPS-acetylene substituted benzene-1,2-diol and naphthalene-2,3-diol were reacted with 2,3-dichloropyrazine, 2,3-dichloroquinoxaline, and 2,3-dichlorobenzoquinoxaline to give a set of six novel and well soluble dioxadiazaacenes. Different reaction conditions for the coupling were tested. Copper catalysis is most effective and gave the best yield of dioxadiazaacenes. The resulting azaoxaacenes were characterized in terms of optical and electronic properties and crystal packing.
The Journal of Organic Chemistry 02/2013; · 4.45 Impact Factor
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ABSTRACT: The other side of the mountain: Changing the framework of diyne systems opens up new cyclization modes for dual gold catalysis. Instead of a 5-endo cyclization and gold vinylidenes a 6-endo cyclization gives rise to gold-stabilized carbenes as key intermediates for selective CH insertions.
Angewandte Chemie International Edition 01/2013; · 13.45 Impact Factor
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ABSTRACT: A three-component reaction of 3-formyl chromones, dialkyl acetylenedicarboxylate, and isocyanides in the presence of [Formula: see text] was used as a highly efficient and practical approach for the synthesis of 3-amino-5-chromenyl-butenolides. High yields and high bond forming efficiency, and simple operations are the advantages of this method. Graphical abstract.
Molecular Diversity 01/2013; · 3.15 Impact Factor
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ABSTRACT: The synthesis, optical, and electrochemical properties as well as solid-state structures of a series of alkynylated, benzannulated selenadiazoles are reported. This set of compounds is compared to the lighter homologue series, the thiadiazoles. The selenadiazoles show head-to-head dimerization in the solid state, while packing of the thiadiazoles was dominated by the steric bulk of the side groups. The Se-N interaction is a supramolecular motif that should drive the effective self-assembly and modulate charge transport when these compounds are used as thin films in devices.
Organic Letters 01/2013; · 5.86 Impact Factor
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ABSTRACT: [Cp*Ir(Pro)Cl] (Pro = prolinato) was identified among a series of Cp*-iridium half-sandwich complexes as a highly reactive and selective catalyst for the alkylation of amines with alcohols. It is active under mild conditions in either toluene or water without the need for base or other additives, tolerates a wide range of alcohols and amines, and gives secondary amines in good to excellent isolated yields.
Organic Letters 01/2013; · 5.86 Impact Factor
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ABSTRACT: A series of dinuclear gold σ,π-propyne acetylide complexes were prepared and tested for their catalytic ability in dual gold catalysis that was based on the reaction of an electrophilic π-complex of gold with a gold acetylide. The air-stable and storable catalysts can be isolated as silver-free catalysts in their activated form. These dual catalysts allow a fast initiation phase for the dual catalytic cycles without the need for additional additives for acetylide formation. Because propyne serves as a throw-away ligand, no traces of the precatalyst are generated. Based on the fast initiation process, side products are minimized and reaction rates are higher for these catalysts. A series of test reactions were used to demonstrate the general applicability of these catalysts. Lower catalyst loadings, faster reaction rates, and better selectivity, combined with the practicability of these catalysts, make them ideal catalysts for dual gold catalysis.
Chemistry 12/2012; · 5.93 Impact Factor
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ABSTRACT: We report the reaction of several N,N'-dihydrotetraazaacenes with oxalylic chloride to give unusual adducts, which were characterized by single crystal X-ray structures.
The Journal of Organic Chemistry 12/2012; · 4.45 Impact Factor
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ABSTRACT: Mobile: The title reaction affords diastereomerically pure 3,4-disubstituted pyrrolidin-2-ones, which are important structural motifs in natural products, in good to high yields. Mechanistic investigations suggest the transformation proceeds through a tandem 1,3-acyloxy migration and a subsequent 1,5-acyloxy migration. DCE=1,2-dichloroethane, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene.
Angewandte Chemie International Edition 12/2012; · 13.45 Impact Factor
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ABSTRACT: Four different synthetic strategies led to a variety of furan-yne systems that contained an aryl system in the tether. Due to the short routes to these systems (four steps or less), a small library of substrates could easily be prepared. These were treated with AuCl(3) or with the Gagosz's catalyst Ph(3) PAuNTf(2) complex. The AuCl(3) -catalyzed reactions delivered highly substituted fluorene derivatives, a class of compounds of great importance as precursors for luminophores with extraordinary abilities. Conversely, a different mechanistic pathway was observed with the cationic gold(I) catalyst. In the latter case, a mechanistically interesting reaction cascade initiated a formal alkyne insertion into the furyl-sp(3) -C bond, which gave indene derivatives as the final products. This new reaction pathway depends on the aromatic moiety in the tether, which stabilizes a crucial cationic intermediate as a benzylic cation.
Chemistry 11/2012; · 5.93 Impact Factor
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ABSTRACT: A sterically shielded cationic NHC gold complex IPr**Au-BArF(24) without solvent coordination has been prepared in situ in CH(2)Cl(2). The monovalent transition metal electrophile, a "soft proton", heterolytically activates the C-B bond of the weakly coordinating counterion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate at room temperature.
Chemical Communications 10/2012; 48(92):11325-7. · 6.17 Impact Factor
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ABSTRACT: (π-Allyl)Ir complexes derived from dibenzocyclooctatetraene and phosphoramidites by cyclometalation are effective catalysts for allylic substitution reactions of linear monosubstituted allylic carbonates. These catalysts provide exceptionally high degrees of regioselectivity and allow the reactions to be run under aerobic conditions. A series of (π-allyl)Ir complexes were prepared and characterized by X-ray crystal structure analyses. An allylic amination with aniline displayed different resting states depending on the presence of a strong base. DFT calculations were carried out on the mechanistic aspects of these reactions. The results suggest that for the (π-allyl)Ir complexes, the formation and reactions with nucleophiles proceed with comparable rates.
Chemistry 09/2012; 18(45):14314-28. · 5.93 Impact Factor
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ABSTRACT: A sterically shielded 3-substituted zwitterionic N,N-dimethylisotryptammonium carboxylate has been synthesized by consecutive chemoselective double alkylation of indole. The carboxylate undergoes a quantitative and unusually facile decarboxylation in dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF) at room temperature. The breaking of a nearly equidistant hydrogen bond by solvent molecules initiates heterolytic CC cleavage. The decarboxylation rate decreases with increasing CO(2) partial pressure, proving the competitiveness of protonation and re-carboxylation of the carbanionic intermediate. Corresponding spiro compounds containing silylene and stannylene moieties show high thermal stability. Addition of an excess of methyllithium to the sodium salt triggers a reaction sequence comprising a deprotonation, carboxylate transfer, and nucleophilic trapping of the rearranged carboxylate by another equivalent of methyllithium. Hydrolytic work-up of the geminal diolate leads to an acetyl product. The role of the sodium counterion and the mechanism of the rearrangement have been unraveled by deuteration experiments.
Chemistry 09/2012; 18(44):14174-85. · 5.93 Impact Factor
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ABSTRACT: Highly reactive gold vinylidene species are used for intermolecular C(sp(3) )H insertions into unactivated alkanes. In addition, they can be regarded as synthons for alkylidene carbenes. Initiated by cyclopropanation of the vinylidene species/alkylidene carbenoide, cyclobutene derivatives are formed in a diastereoselective fashion by a ring-enlargement cascade in only one step.
Angewandte Chemie International Edition 09/2012; 51(42):10633-7. · 13.45 Impact Factor
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ABSTRACT: A new, highly efficient, and atom-economic access to a series of functionalized 2,5-disubstituted oxazoles from propargylic amides is reported. A series of propargylic amides were transformed to the corresponding alkylideneoxazolines by a gold(I) catalyst. The next step was an autoxidation to hydroperoxides bearing the heteroaromatic oxazoles. Experiments addressing the reaction mechanism reveal a radical pathway for this autoxidation process. The hydroperoxides could conveniently be converted to the corresponding alcohols by reduction with sodium borohydride.
The Journal of Organic Chemistry 07/2012; 77(15):6394-408. · 4.45 Impact Factor
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ABSTRACT: It takes al-kynes: The formation of furyl-substituted heterocycles from furanynes with donor groups on the furan-alkyne tether and mechanistic control experiments indicate the involvement of open-chained carbenium ions in the overall insertion of an alkyne into a C-C bond, rather than the usual spirocyclic intermediates.
Chemistry 07/2012; 18(34):10480-6. · 5.93 Impact Factor
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ABSTRACT: Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescence behavior is analyzed by emission spectroscopy and interpreted by using time-dependent density functional calculations as largely due to different excited-state dynamics of [6](2+) and [9](2+) . The geometries of both radicals [6](.+) and [9](.+) and excited states {[6](2+) }* and {[9](2+) }* are substantially different from those of the parent ground-state molecules.
Chemistry 07/2012; 18(34):10677-88. · 5.93 Impact Factor
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ABSTRACT: A series of furan-yne systems was transformed into the corresponding tetrasubstituted annelated phenol derivatives that bear one bromo group. The two-step procedure consisted of a phenol synthesis and a subsequent electrophilic bromination with N-bromosuccinimide (NBS). The reactions can be performed in a one-pot procedure with the same precatalyst. The halogenation reaction is highly selective only in the presence of the gold catalyst. En-diyne substrates were also suitable starting materials; then the pentasubstituted aromatic core showed a completely different substitution pattern for the phenolic products. Furthermore, a one-pot protocol that consisted of a gold-catalyzed phenol synthesis, a gold-catalyzed halogenation reaction, and a palladium-catalyzed Suzuki coupling was established. The overall efficiency of this procedure was excellent and the substrate scope of the reaction was broad.
Chemistry 05/2012; 18(26):8113-9. · 5.93 Impact Factor
