The different roles of a cationic gold(i) complex in catalysing hydroarylation of alkynes and alkenes with a heterocycle

Abstract

The mechanism of twofold hydroarylation of terminal alkynes with pyrrole catalyzed by a cationic gold(i) complex was investigated using DFT. It was found that while both the hydroarylation reactions proceed via a Friedel-Crafts-type mechanism, the first hydroarylation is directly promoted by gold(i) but the second hydroarylation by a proton released through interaction of the alkene product with gold-bound acidic organic species such as acetic acid and terminal alkynes.

The Gold‐Catalyzed Hydroarylation of Alkynes with Electron‐Rich Heteroarenes – A Kinetic Investigation and New Synthetic Possibilities

“…Moreover, from the obtained kinetic data it became obvious that protonsr eversibly derived from the formation of s,p-acetylide complexes from the terminal alkynes are crucial for the second step of the addition cascade.T his observation is in accordance with recently published density functional theory (DFT) calculations. [10] By employingt he orthogonal reactivity of gold and ap roton for the two reactions teps,t he synthesiso fh etero-di-adducts could be achieved in moderate to good yields (10-84%). Basedo nt he collected kinetic data andt he possibility of converting the obtained intermediates,t his opens up news ynthetic possibilities for further applications in the synthesis of hetero-addition products.…”

“…[7b] In 2007, Echavarren et al observedt he goldcatalyzed mono-hydroarylation reaction of alkynes and indoles. [7e] No detaileds tudies regarding the kinetics of the gold-catalyzed transformation have been reported to date.T he mechanisticd etails were recent-ly determined theoretically by DFT calculations, [10] however, without any experimental proof.T his encouraged us to shed light on the kineticso ft hese transformationsw ith the aim to obtain furtherm echanistic details as well as the possibility to extend the synthetic scope of this useful reaction. Ther esults of our study are summarized in this contribution.…”

Gold(I) Complexes in Ionic Liquids: An Efficient Catalytic System for the C‐H Functionalization of Arenes and Heteroarenes under Mild Conditions

“…[22h] Thus, it seems that the second hydroarylation is much faster than the first one, and it has been argued in the literature that it may even not involve gold catalysis but rather catalysis by traces of acid present in the system. [22h], It is important to remark that no protection of the indole N‐H function is necessary for efficient reaction, as use of unprotected indole furnishes a comparable reaction yield (entry 4). The catalytic activity recorded in ionic liquid compares favourably with the one reported by the group of Hashmi with the same catalytic system in acetonitrile at room temperature; 85 % alkyne conversion was reported after 10 hours reaction time, albeit with 2 mol‐% catalyst instead of 0.5 mol‐% and with a heteroarene:alkyne ratio of 5:1 instead of just 2:1 (stoichiometric ratio), as in the present case.…”

Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights

“…Remarkably, products of double hydroarylation of the triple bond are generally not observed when regular arenes are employed as substrates. A computational study by the group of Ariafard [120], using the Me 3 PAu + -catalyzed hydroarylation of propyne by pyrrole in the presence of acetic acid as a model system, suggested multiple, competitive pathways for the double hydroarylation product with overall barrier similar to that of the first hydroarylation. In all these pathways, the gold center is not directly involved in the second hydroarylation process, but it rather acts indirectly by promoting the generation of protons which in turn catalyze the hydroarylation.…”