Reactant-induced photoactivation of in situ generated organogold intermediates leading to alkynylated indoles via Csp2-Csp cross-coupling

Formation of 3-Alkynylidenephthalides by Gold(I)-Catalyzed Alkynylative Cyclization of o-Alkynylbenzoic Acids under Visible Light Irradiation

Herein, we report a Csp2-Csp cross-coupling process involving the merger of gold catalysis and visible light photocatalysis leading to the alkynylative cyclization of o-alkynyl benzoic acids. The corresponding and previously undescribed alkynylidenephthalide products were obtained as mixtures of E:Z isomers. The key C-C bond formation is based on the photoactivation of the oxidative addition of an alkynyliodide to a vinylgold(I) intermediate resulting from an initial 5-exo-dig cyclization pathway, as supported by mechanistic studies including DFT calculations.

Photosensitized Reductive Elimination of Gold(III) to Enable Esterification of Aryl Iodides with Carboxylic Acids

Compared to the well-established transition metal-catalyzed cross-coupling reactions, Au(I)/Au(III)-catalyzed cross-coupling reactions have lagged behind. Despite some advancements, achieving gold-catalyzed C-O coupling with carboxylic acids via an Au(III) carboxylate intermediate remains challenging due to the thermal unfavorability of the critical reductive elimination step. Here, we present the first photosensitized reductive elimination of gold(III) to enable esterification of aryl iodides with carboxylic acids. In the presence of a (P, N)-gold(I) catalyst and a photosensitizer benzophenone under blue LED irradiation, esterification derivatives were obtained from aryl iodides with both aryl and alkyl (1°, 2°, 3°) carboxylic acids. Mechanistic and modeling studies support that energy transfer (EnT) from a photosensitizer produces an excited-state gold(III) complex that couples aryl iodides with carboxylic acids. This photoinduced energy-transfer strategy has been applied in several other photosensitized gold catalysis reactions, indicating its potential for further applications.

Straightforward Access to Isoindoles and 1,2-Dihydrophthalazines Enabled by a Gold-Catalyzed Three-Component Reaction

We describe herein a gold-catalyzed three-component reaction of o-alkynylbenzaldehydes, aryldiazonium salts, and trimethoxybenzene. This process enables the one-pot formation of valuable isoindoles and 1,2-dihydrophathalazines. The regioselectivity of the reaction is dictated by the nature of the aryldiazonium salt. Noticeably, the reaction is performed at room temperature under mild conditions and tolerates a variety of functional groups on both the o-alkynylbenzaldehyde and the aryldiazonium salt. Experimental mechanistic studies suggest that it is catalyzed by arylAu(III) species.

Indium(III)-Catalyzed Haloalkynylation Reaction of Alkynes

Green chemistry strives for sustainability at the molecular level and is gaining increasing relevance in the development of chemical reactions. The haloalkynylation reaction is a highly atom-economical C-C coupling reaction that was previously only achieved using transition metal catalysts. It enables the introduction of an alkyne unit and a halogen atom into the target molecule. Herein, we present a haloalkynylation reaction catalyzed by indium(III) halides. The use of indium(III) bromide as a catalyst leads exclusively to the cis addition products with yields up to 86 %. In addition, iodoacetylenes can be applied for the first time for the haloalkynylation reaction of internal alkynes which is an important step forward in the development of industrially relevant and sustainable catalysts. In contrast to gold catalysis, which proceeds via a similar mechanism, the use of alkyl-substituted haloacetylenes as reagents is also possible. Based on 13C labeling experiments and quantum chemical calculations, we postulate two possible mechanisms for the indium(III)-catalyzed haloalkynylation reactions.

Gold-Catalyzed 1,2-Dicarbofunctionalization of Alkynes with Organohalides

Herein, we report the first gold-catalyzed 1,2-dicarbofunctionalization of alkynes using organohalides as non-prefunctionalized coupling partners. The mechanism of the reaction involves an oxidative addition/π-activation mechanism in contrast to the migratory insertion/cis-trans isomerization pathway that is predominantly observed with other transition metals yielding products with anti-selectivity. Mechanistic insights include several control experiments, NMR studies, HR-MSMS analyses, and DFT calculations that strongly support the proposed mechanism.

Gold(I)-Catalyzed Tandem Cyclization/Hydroarylation of o-Alkynylphenols with Haloalkynes

A convenient and mild protocol for the gold-catalyzed intermolecular coupling of o-alkynylphenols with haloalkynes to give vinyl benzofurans is reported. In this work, the gold catalyst SIPrAuCl and the co-catalyst NaBARF would corporately promote the intramolecular cyclization of the o-alkynylphenol to benzofuran, and then a selective hydroarylation of benzofuran to haloalkyne was catalyzed by the same catalysts. Computational studies suggest that the hydroarylation process takes place via a concerted nucleophilic attack pathway of the benzofuran to the C2 carbon of the activated haloalkyne, and reveal the original driving force of this hydroarylation process.