Addition of pyrroles onto terminal alkynes catalyzed by a dinuclear ruthenium (II) complex

An Intramolecular Reaction between Pyrroles and Alkynes Leads to Pyrrole Dearomatization under Cooperative Actions of a Gold Catalyst and Isoxazole Cocatalysts

The gold-catalyzed one-pot synthesis of 3H-benzo[e]isoindoles (3) from a mixture of isoxazole (2) and diynamides (1) is described. This tandem catalysis involves two separate steps: (i) initial synthesis of 2-(3-pyrrolyl)-1-alkynylbenzenes and (ii) a novel alkyne/pyrrole coupling reaction through pyrrole dearomatization. Our control experiments reveal the cooperative action of the gold catalyst and isoxazole cocatalyst to enable the novel alkyne/pyrrole coupling leading to a 1,2-acyl shift.

Metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes

Metal-catalyzed highly Markovnikov-type selective hydrofunctionalization of terminal alkynes provides a straightforward and atom-economical route to access 1,1-disubstituted alkenes, which have a wide range of applications in organic synthesis. However, the highly Markovnikov-type selective transformations are challenging due to the electronic and steric effects during the addition process. With the development of metal-catalyzed organic synthesis, different metal catalysts have been developed to solve this challenge, especially for platinum group metal catalysts. In this perspective, we review homogeneous metal-catalyzed Markovnikov-type selective hydrofunctionalization of terminal alkynes according to the classified element types as well as reaction mechanisms. Future avenues for investigation are also presented to help expand this exciting field.

Frustrated Lewis pair-catalyzed double hydroarylation of alkynes with N-substituted pyrroles

Metal-free hydroarylation of alkynes with N-substituted pyrroles is shown to be efficiently mediated by B(C₆F₅)₃ to yield variants of dipyrrole methanes. The mechanism is shown to proceed via an FLP addition pathway.

Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides

Although the ruthenium-catalyzed C–H arylation of arenes bearing directing groups with haloarenes is well-known, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η⁶-arene-ligand-free Ru(II) catalyst. Indeed, upon initial pivalate-assisted C–H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C–H activation is both reversible and kinetically significant. Computational studies support a concerted metalation–deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.

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

Hydroarylation of alkenes is promoted by a proton released by interaction of a cationic gold complex with an acidic species.

An efficient Au(i) catalyst for double hydroarylation of alkynes with heteroarenes

Double hydroarylation of alkynes with heteroarenes under mild conditions catalyzed by Au(i) are now reported.