Constructing products of high synthetic value from inexpensive and abundant starting materials is of great importance. Aryl iodides are essential building blocks for the synthesis of functional molecules, and efficient methods for their synthesis from chemical feedstocks are highly sought after. Here we report a low-cost decarboxylative iodination that occurs simply from readily available benzoic acids and I2. The reaction is scalable and the scope and robustness of the reaction is thoroughly examined. Mechanistic studies suggest that this reaction does not proceed via a radical mechanism, which is in contrast to classical Hunsdiecker-type decarboxylative halogenations. In addition, DFT studies allow comparisons to be made between our procedure and current transition-metal-catalyzed decarboxylations. The utility of this procedure is demonstrated in its application to oxidative cross-couplings of aromatics via decarboxylative/C–H or double decarboxylative activations that use I2 as the terminal oxidant. This strategy allows the preparation of biaryls previously inaccessible via decarboxylative methods and holds other advantages over existing decarboxylative oxidative couplings, as stoichiometric transition metals are avoided.

We have discovered that the dba ligand in the commonly used Pd2(dba)3·CHCl3 cross-coupling pre-catalyst is susceptible to bis-arylation when used in the presence of aryl iodides. The in situ formed dbaAr2 ligands result in Pd-species with altered catalytic activity. In the case of study, the room temperature C3 arylation of benzo[b]thiophenes with aryl iodides, we have observed a marked catalyst deactivation when dba is arylated with electron-deficient aryl iodides, accounting for the poor yields obtained in the C3 arylation reactions with these aryl iodides. Based on these studies, we report a new catalytic system, employing a dba-free Pd catalyst, which allows for the first time the direct C3 arylation of benzo[b]thiophenes with electron-deficient aryl iodides at room temperature.

Methods for the determination of 2H KIEs at natural abundance of deuterium have not been widely used due to the requirement for very long NMR times or large reaction scale. We previously reported a simple methodology for reducing these restrictions by the addition of a small amount of deuterated substrate. Herein, we evaluate the deuterium loadings that give the lowest errors in the determination of 2H KIEs. Our simulations indicate that our approach leads to a 4000-fold reduction in NMR time over natural abundance methods.

The beginning of the 21st century has seen tremendous growth in the field of decarboxylative activation. Benzoic acid derivatives are now recognised as atom-economic alternatives to traditional cross-coupling partners, and they also benefit from being inexpensive, readily available and shelf-stable reagents. In this microreview we discuss recent developments in the coupling of benzoic acid derivatives either with an arene or with a second benzoic acid derivative, a process often termed decarboxylative oxidative cross-coupling. These procedures offer great promise for the development of highly selective and atom-economic cross-couplings.

The ability to selectively functionalise a specific C–H bond is a long-standing challenge due to the ubiquity of such bonds in organic molecules. One of the most common approaches to overcome this obstacle consists of installing directing groups into substrates to direct the functionalisation towards the desired C–H bond, leaving behind the directing group in the molecule. Alternatively, carboxylic acids have been employed as traceless directing groups that are easily removed after carboxylic acid-directed installation of the desired functionality. This review focuses on the development of this concept and its application to organic synthesis during the last decade.

The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C–H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C–H activation on electron-deficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh3)Ag-carboxylate is responsible for the C–H activation step in the Pd-catalyzed arylation of Cr(CO)3-complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C–H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C–H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C–H functionalization methodologies.

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 first example of a regioselective β-arylation of benzo[b]thiophenes and thiophenes at room temperature with aryl iodides as coupling partners is reported. This methodology stands out for its operational simplicity: no prefunctionalization of either starting material is required, the reaction is insensitive to air and moisture, and it proceeds at room temperature. The mild conditions afford wide functional group tolerance, often with complete regioselectivity and high yields, resulting in a highly efficient catalytic system. Initial mechanistic studies, including 13C and 2H KIEs, suggest that this process occurs via a concerted carbo-palladation across the thiophene double bond, followed by a base-assisted anti-elimination.

Direct arylations of pyridines are challenging transformations due to the high Lewis basicity of the sp2-nitrogen. The use of carboxylates as directing groups is reported, facilitating the Pd-catalyzed C–H arylation of this difficult class of substrates. This methodology allows regioselective C3/C4 arylation, without the need to use solvent quantities of the pyridine, and using low-cost chloro- and bromoarenes as coupling partners. Furthermore, carboxylates could be employed as traceless directing groups through a one-pot C–H arylation/Cu(I)-mediated decarboxylation sequence, thereby accessing directing-group-free pyridine biaryls.

The first methodology for Au(I/III)-catalyzed oxidative cross-coupling of arenes via double C–H activation has been developed. The reaction is fully selective for the cross-coupling between electron-rich hetero-/carbocyclic arenes and electron-poor arenes bearing relatively acidic C–H bonds. The inherently high cross-selectivity of the system obviates the need for directing groups or a large excess of one of the coupling partners.

Salicylic acids are shown to be readily available and versatile starting materials that easily undergo a tandem arylation–protodecarboxylation process under Pd-catalysis. The corresponding meta-arylphenols can subsequently be easily transformed into a variety of meta-functionalized biaryls, highlighting the versatility of this approach to access this structural motif.

We report the first example of a general, exhaustive Pd-mediated cross-coupling of polychloroarenes in the presence of a deficit of nucleophiles, mediated by the highly active PEPPSI-IPent catalyst. Our results indicate that this catalyst system may be applicable to the pseudo-living polymerisation of chloroarene monomers.

Current approaches to achieve site selectivity in the C–H activation of arenes involve the use of directing groups or highly electron-poor arenes. In contrast, simple arenes, such as anisole, are characterized by poor reactivity and selectivity. We report that π-complexation to a Cr(CO)3 unit enhances the reactivity of anisoles providing an unprecedented ortho-selective arylation. This mild methodology can be used for the late stage functionalization of bioactive compounds containing the anisole motif, allowing the construction of novel organic scaffolds with few synthetic steps.

We report the first example of a general, exhaustive Pd-mediated cross-coupling of polychloroarenes in the presence of a deficit of nucleophiles, mediated by the highly active PEPPSI-IPent catalyst. Our results indicate that this catalyst system may be applicable to the pseudo-living polymerisation of chloroarene monomers.

The ability to selectively functionalise a specific C–H bond is a long-standing challenge due to the ubiquity of such bonds in organic molecules. One of the most common approaches to overcome this obstacle consists of installing directing groups into substrates to direct the functionalisation towards the desired C–H bond, leaving behind the directing group in the molecule. Alternatively, carboxylic acids have been employed as traceless directing groups that are easily removed after carboxylic acid-directed installation of the desired functionality. This review focuses on the development of this concept and its application to organic synthesis during the last decade.

Salicylic acids are shown to be readily available and versatile starting materials that easily undergo a tandem arylation–protodecarboxylation process under Pd-catalysis. The corresponding meta-arylphenols can subsequently be easily transformed into a variety of meta-functionalized biaryls, highlighting the versatility of this approach to access this structural motif.