Conjugated 1,5-diynes bearing two aromatic units at the alkyne termini were converted in the presence of a gold catalyst. Under mild conditions, aryl-substituted dibenzopentalenes were generated. Calculations predict that aurated vinyl cations are key intermediates of the reaction. A bidirectional approach provided selective access to the angular annulated product in high yield, which was explained by calculations.

Differently substituted terminal alkynes that bear sulfonate leaving groups at an appropriate distance were converted in the presence of a propynyl gold(I) precatalyst. After initial formation of a gold acetylide, a cyclization takes place at the β-carbon atom of this species. Mechanistic studies support a mechanism that is related to that of dual gold-catalyzed reactions, but for the new substrates, only one gold atom is needed for substrate activation. After formation of a gold vinylidene complex, which forms a tight contact ion pair with the sulfonate leaving group, recombination of the two parts delivers vinyl sulfonates, which are valuable targets that can serve as precursors for cross-coupling reactions, for example.

A number of saturated abnormal N-heterocyclic carbene (NHC) complexes of gold, in combination with KBAr(F) 4 as activator, were successfully applied in the chemoselective addition of hydrazine to alkynes. The reaction proceeds even at room temperature, which was not possible to date with gold catalysts. The reaction can be applied to a number of substituted arylalkynes. With alkylalkynes the yields are low. The saturated abnormal NHC ligands are resistant to isomerization to the saturated normal NHC coordination mode under basic reaction conditions. Under acidic conditions, a simple protonation at the nitrogen atom not neighboring the carbene center was observed and unambiguously characterized by an X-ray crystal-structure analysis. Computational studies confirm that such an isomerization would be highly exothermic, the observed kinetic stability probably results from the need to shift two protons in such a process.

Six different cationic gold(I) complexes LAu+ were converted to the corresponding di(alkoxy)carbenium ions by reaction with ethyl 2,5-dimethylhexa-2,3-dienoate. These conversions were monitored by in situ IR spectroscopy; at room temperature they proceeded in only a few seconds. The ligands L are based on the most popular ligand types in gold catalysis: phosphanes, phosphites, carbenes, and isonitriles. The di(alkoxy)carbenium ions were stable, not short-lived intermediates, and could be characterized. This allowed the kinetic study of the next step, the hydrolytic cleavage to the Hammond-type vinylgold species. Depending on the ligand on gold, large rate differences were detected. Computational chemistry revealed a correlation of the experimental reaction rates with the LUMO energies of the di(alkoxy)carbenium species and the direct influence of the ligand on gold on these LUMO energies. Thus, the di(alkoxy)carbenium ion could be utilized as an easy to use benchmark system for the electronic characterization of LAu+ catalysts by theory, spectroscopy, and kinetic experiments.

cis-Enediyne systems bearing twon onterminal alkyne functionalitiesw ere transformed in the presence of ag oldc atalyst. As elective6 -endodig-cyclization generates mono-aurated phenyl cation intermediates,h ighe nergy species that are able to activate even primary sp 3 -C-H-bonds. Via insertion into intramolecularly offered, unactivated C-H-bonds, penta-substituted benzene derivatives are obtaineda sf inalp roducts. In most casess elective insertions into the g-sp 3 -C-H bonds of the offered tethers were observed. Scheme 1. Reported chemistry of diynes and plannedaccess to intermediate VIII.

In am odular template synthesis,unsaturated NHC complexes of gold, palladium andp latinum were synthesizedf rom simplem etal salts,i sonitriles and aminesw ith acetal or ketal groups.U pon the addition of aminesw ith tethereda cetal or ketal moieties to the metal-activated isonitrile,f irst nitrogen acyclic carbene (NAC)c omplexes are formed. These undergo ring closure and elimination to the unsaturated NHC complexes upon addition of acid. This simples trategyo pens an attractive and fast approach to NHC complexes of gold, palladium and platinum. Them odular approach allowsafast modification and is well-suited for the synthesiso fu nsymetrically and symmetricallys ubstituted unsaturated NHC complexes.Scheme 1. NHC-Synthesis via metal isonitrile precursors; left:i ntermolecular process,r ight:i ntramolecular process.

Abstract1,5‐Diyne systems bearing one terminal and one benzyl‐ or allyl‐substituted alkyne attached to an aromatic backbone were converted in the presence of a gold catalyst. In a dual gold‐catalyzed process, gold vinylidenes are formed that selectively undergo formal CH insertion into the C(sp2)–H bond of the offered unsaturated systems. If H atoms are present in the propargylic position, a subsequent isomerization to the aromatic system takes place leading to 9H‐fluorene and 11H‐benzo[b]fluorene derivatives as final products. In the case of a quaternary carbon in the propargylic position no further aromatization is observed and 10H‐benzo[b]fluorene derivatives are obtained in high yield.magnified image

The first examples of amphiphilic reactivity in the context of enantioselective catalysis are described. Commercially available π-allyliridium C,O-benzoates, which are stable to air, water and SiO chromatography, and are well-known to catalyze allyl acetate-mediated carbonyl allylation, are now shown to catalyze highly chemo-, regio- and enantioselective substitutions of branched allylic acetates bearing linear alkyl groups with primary amines.