In this tutorial review directed towards chemists interested in synthesis or catalysis, the application of gold catalysis in total synthesis is summarised and the mode of activation of the substrate by the gold catalyst is discussed.

In this critical review, the strongly increasing amount of new applications of gold catalysis in total synthesis is summarised and, for the new developed methods, the mode of activation of the substrate by the gold catalyst is discussed (47 references).

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.

Terminal 1,2-dialkynylarenes undergo an unexpected cyclization hydroarylation reaction toward naphthalene derivatives in benzene as the solvent. The regioselectivity of the reaction can be controlled by careful catalyst tuning. Also, the preparation of a bench-stable cationic amine complex or simple heterogenization of the catalyst on neutral aluminum oxide, which enables efficient catalyst recycling, was possible. Intensive mechanistic investigations were undertaken, giving new insights into the so-far underestimated role of acetylides in gold chemistry. The gold plays a fascinating dual role serving to both catalyze the reaction and activate the substrate by Au−C-σ bond formation. Evidence of gem-diaurated compounds playing an important part for gold catalysis is also reported.

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.