Die Katalyse durch Gold ist schnell ein “heißes Thema” der Chemie geworden – fast wöchentlich werden neue Entdeckungen gemacht. Gold ist gleichermaßen als heterogener wie auch als homogener Katalysator aktiv, und im folgenden Aufsatz wollen wir diese beiden Facetten gemeinsam präsentieren, um so die vielfältigen Möglichkeiten der Gold‐Katalyse darzulegen. Die neuesten Entdeckungen werden im historischen Kontext diskutiert, Hauptziel ist aber, die neuen Optionen aufzuzeigen, die Gold‐Katalysatoren dem Synthesechemiker bieten – besonders auf den Gebieten der Redoxreaktionen und nucleophilen Additionen an π‐Systeme. Oft erweist sich Gold sogar als guter Katalysator für zuvor unbekannte Reaktionen, und in diesem Bereich gibt es mit Sicherheit noch viel zu entdecken.

In this critical review the applications of gold catalysed reactions in total synthesis during the years since our last article are reviewed. At the end of this article a literature analysis is conducted to evaluate the progress in this field.

Under visible-light irradiation, the gold-catalyzed intermolecular difunctionalization of alkynes with aryl diazonium salts in methanol affords a variety of α-aryl ketones in moderate to good yields. In contrast to previous reports on gold-catalyzed reactions that involve redox cycles, no external oxidants or photosensitizers are required. The reaction proceeds smoothly under mild reaction conditions and shows broad functional-group tolerance. Further applications of this method demonstrate the general applicability of the arylation of a vinyl gold intermediate instead of the commonly used protodemetalation step. This step provides facile access to functionalized products in one-pot processes. With a P,N-bidentate ligand, a stable aryl gold(III) species was obtained, which constitutes the first direct experimental evidence for the commonly postulated direct oxidative addition of an aryl diazonium salt to a pyridine phosphine gold(I) complex.

At room temperature under mild photochemical conditions, namely irradiation with a simple blue light LED, gold(i) chloro complexes of both phosphane and carbene ligands in combination with aryldiazonium salts afford arylgold(iii) complexes. With chelating P,N-ligands cationic six- or five-membered chelate complexes were isolated in the form of salts with weakly coordinating counter anions that were brought in from the diazonium salt. With monodentate P ligands or N-heterocyclic carbene ligands and diazonium chlorides neutral arylgold(iii) dichloro complexes were obtained. The coordination geometry was determined by X-ray crystal structure analyses of representative compounds, a cis arrangement of the aryl and the phosphane ligand at the square planar gold(iii) center is observed.

The use of the combination of homogeneous gold-catalysts and alkynes in organic synthesis is reviewed from its beginnings in C-N-bond formation to the newest developments in C-C-bond formation. The common basic principle of these reactions is discussed. Special attention is devoted to the question where the gold catalysts are superior to either other catalysts or more traditional synthetic approaches to the product molecules.Transition metal catalysis has become one of the most important tools in organic synthesis. It allowed entirely new transformations which were not possible previously by "traditional" organic reactions and thus significantly increased the efficiency of synthesis. It also made retrosynthetic analysis more demanding as many of the transformations go along with a remarkable increase in molecular complexity (1) which makes the relationship between the product and the starting material more difficult to recognize. In many of these reactions, especially in the case of late transition metals, C-C multiple bonds in either alkenes or alkynes, are the site of reaction. Theoretical backgroundIn the field of homogeneous gold catalysis the alkynes 1, which have the structural motive of a C-C-triple bond, belong to the most popular substrates. The reason for that popularity is the high reactivity of the alkynes which originates from their electronic structure (2). Often the corresponding alkenes with their C-C-double bond are less reactive.On one hand, the alkynes possess two orthogonal -orbitals high in energy occupied by two electrons each. These react with electrophilic reagents (E) like halogens in organic synthesis or electrophilic metal centers like gold (in the oxidation states I or III) in the field of transition metal catalysis (3,4). In the interaction with a metal center both the -orbital in the plane of metal co-ordination and theorbital perpendicular to it are able to interact with the dorbitals of the metal.On the other hand, the lowest unoccupied orbital of the alkynes is low in energy and thus eagerly react with strong nucleophiles like for example ethyne 2 with catalytical amounts of alkoholates in the Reppe synthesis of vinyl ethers 3 (5).Most unfortunately, weak nucleophiles (Nu) do not react directly with the alkynes, although this is often desired in organic synthesis. But the alkyne can be activated by co-ordination to the electrophilic gold complexes as mentioned above. This co-ordination withdraws electron

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Die Gold‐Katalyse ist ein sehr aktives Gebiet im Feld der Katalyseforschung. Wöchentlich werden neue Reaktionen publiziert, oft werden erstaunliche Konnektivitätsänderungen beobachtet, die Zahl der Anwendungen in der Totalsynthese steigt …︁ – aber was sind die Mechanismen dieser Reaktionen? Fundierte Informationen können aus dem Wissen über Zwischenstufen dieser Reaktionen erhalten werden.

In this critical review the reactivity patterns observed with different types of diyne substrates in gold catalysis are discussed. Apart from the many examples from homogeneous catalysis, the few examples from heterogeneous gold catalysis are also included. With a proper arrangement of the two alkynes unique and exciting reactivity patterns like 1,3-carbonyl transpositions, carbene transfer reactions, cascade annulations, macrocyclisations or the formation of gold vinylidene intermediates are observed. These reactions are of interest for organic synthesis, for pharmaceutical and medicinal chemistry and for material science.