Enantioselective gold-catalysis is emerging as a powerful tool in organic synthesis for the stereoselective manipulation of unfunctionalized unsaturated hydrocarbons. Despite the exponential growth, the molecular complexity of common chiral gold complexes generally prevents a complete description of the mechanism steps and activation modes being documented. In this study, we present the results of a combined experimental-computational (DFT) investigation of the mechanism of the enantioselective gold-catalyzed allylic alkylation of indoles with alcohols. A stepwise S(N)2'-process (i.e. anti-auroindolination of the olefin, proton-transfer, and subsequent anti-elimination [Au]-OH) is disclosed, leading to a library of tricyclic-fused indole derivatives. The pivotal role played by the gold counterion, in terms of molecular arrangement (i.e. "folding effect") and proton-shuttling in restoring the catalytic species, is finally documented.

The synthesis of architecturally complex polycyclic fused indolines is achieved in a chemo-, regio-, and stereodefined manner, via an enantioselective gold-catalyzed cascade hydroindolination/iminium trapping synthetic sequence. Highly functionalized tetracyclic fused furoindolines (2) and dihydropyranylindolines (4) are synthesized in moderate to good yields and enantiomeric excesses of up to 87%.

SummaryOver the recent years, the nucleophilic manipulation of inactivated carbon–carbon double bonds has gained remarkable credit in the chemical community. As a matter of fact, despite lower reactivity with respect to alkynyl and allenyl counterparts, chemical functionalization of isolated alkenes, via carbon- as well as hetero atom-based nucleophiles, would provide direct access to theoretically unlimited added value of molecular motifs. In this context, homogenous [Au(I)] and [Au(III)] catalysis continues to inspire developments within organic synthesis, providing reliable responses to this interrogative, by combining crucial aspects such as chemical selectivity/efficiency with mild reaction parameters. This review intends to summarize the recent progresses in the field, with particular emphasis on mechanistic details.

Indoles from scratch: A gold(I)/N-heterocyclic carbene complex (IPr=1,3-di(isopropylphenyl)imidazol-2-ylidene) was found to be particularly effective as a catalyst, enabling the one-pot synthesis of tricyclic azepinoindoles by an unprecedented cascade reaction. Readily available substrates, high chemoselectivity, good yields, and water as the only stoichiometric by-product are some of the main advantages of this method.

All at once: The simultaneous synthesis and enantioselective functionalization of an indole core is achieved with the assistance of chiral cationic AuI complexes. A range of vinyloxazino‐[4,3‐a]indoles is obtained by a cascade process in a highly enantioselective manner (see scheme; L=chiral diphosphine).

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Thumbnail image of graphical abstract\ud \ud The gold standard: A gold-catalyzed cascade reaction sequence for the preparation of polycyclic fused indole cores exploits the ready availability and chemical flexibility of propargylic alcohols. The desired tri- or tetracyclic compounds are obtained in good yields with water as the only stoichiometric by-product

Suzuki-Miyaura reactions of aryl bromides and arylboronic acids proceed in good to excellent yields in a pyrrolidinium ionic liquid by using a preformed air stable and easily handled triethylammonium-tagged diphenylphosphine palladium(II) complex (2). The reaction requires short reaction times and mild temperature conditions and does not show any tendency towards the formation of palladium black. After extraction of the product, the catalyst containing ionic liquid phase is easily recycled for 6 times, with no significant loss of catalytic activity.