Pd-Catalyzed Decarboxylative Arylation of Thiazole, Benzoxazole, and Polyfluorobenzene with Substituted Benzoic Acids

Accessing C2-Functionalized 1,3-(Benz)azoles through Transition Metal-Catalyzed C-H Activation

The skeletal presence of 1,3-azoles in a variety of bioactive natural products, pharmacophores, and organic materials demands the derivatization of such heteroarenes regioselectively. Plenty of cross-coupling as well as cyclocondensation reactions have been performed to build up these skeletons but remained commercially unrealizable. A couple of severe drawbacks are faced by these traditional protocols that require a more straightforward strategy to obviate them. Transition metal-catalyzed C-H functionalization has emerged as a superior alternative in that context. 1,3-Azoles and their benzo counterparts have been extensively functionalized exploiting both noble and earth-abundant transition metals. Lately, C-2 functionalization have gained much traction due to the ease of attaining high regioselectivity and installation of synthetically manipulative functionalities. This critical review presents a bird's eye view of all major C-2 functionalization of (benz)azoles catalyzed by a diverse set of metals performed over the past 15 years.

Wonderful fusion of organofluorine chemistry and decarboxylation strategy

Decarboxylation strategy has been emerging as a powerful tool for the synthesis of fluorine-containing organic compounds that play important roles in various fields such as pharmaceuticals, agrochemicals, and materials science. Considerable progress in decarboxylation has been made over the past decade towards the construction of diverse valuable fluorinated fine chemicals for which the fluorinated part can be brought in two ways. The first way is described as the reaction of non-fluorinated carboxylic acids (and their derivatives) with fluorinating reagents, as well as fluorine-containing building blocks. The second way is dedicated to the exploration and the use of fluorine-containing carboxylic acids (and their derivatives) in decarboxylative transformations. This review aims to provide a comprehensive summary of the development and applications of decarboxylative radical, nucleophilic and cross-coupling strategies in organofluorine chemistry.

Recent Advances in the Synthesis and Applications of 2-Arylbenzothiazoles

This review firstly covers the applications of 2-arylbenzothiazoles as amyloid imaging agents, antitumor agents, and organic luminescent materials. Then we review the recent advances in the synthesis of 2-arylbenzothiazole derivatives. On the one hand, we introduce the approaches for construction of the 2-arylbenzothiazole core, including the following categories: (i) classic condensation of 2-aminothiophenols, (ii) direct arylation of benzothiazoles, (iii) intramolecular cyclization of thiobenzanilides, and (iv) tandem cyclization of anilines/ nitroarenes­ with elemental sulfur or sulfides. On the other hand, the transition-metal-catalyzed direct C–H functionalizations of 2-aryl­benzothiazoles are also involved in this review.

1 Introduction

2 Applications of 2-Arylbenzothiazoles

3 Construction of the 2-Arylbenzothiazole Core

4 Synthesis 2-Arylbenzothiazoles via Direct C–H Functionalization

5 Conclusion

Palladium/copper-catalyzed decarbonylative heteroarylation of amides via C–N bond activation

A novel strategy for the synthesis of 2-arylated oxazole derivatives via palladium/copper-catalyzed decarbonylative heteroarylation of amides via C–N bond activation by ground-state destabilization is reported.

Decarboxylative Suzuki–Miyaura coupling of (hetero)aromatic carboxylic acids using iodine as the terminal oxidant

A novel methodology for the decarboxylative Suzuki–Miyaura-type coupling of carboxylic acids with arylboronic acids has been developed.

Beyond the traditional roles of Ag in catalysis: the transmetalating ability of organosilver(i) species in Pd-catalysed reactions

The role of silver salts in Pd-catalysed C–C bond forming transformations.

A Predictive Model for the Decarboxylation of Silver Benzoate Complexes Relevant to Decarboxylative Coupling Reactions

Decarboxylative coupling reactions offer an attractive route to generate functionalized arenes from simple and readily available carboxylic acid coupling partners, yet they are underutilized due to limitations in the scope of carboxylic acid coupling partner. Here we report that the field effect parameter (F) has a substantial influence on the rate of decarboxylation of well-defined silver benzoate complexes. This finding provides the opportunity to surpass current substrate limitations associated with decarboxylation and to enable widespread utilization of decarboxylative coupling reactions.

Palladium-catalyzed decarboxylative, decarbonylative and dehydrogenative C(sp2)-H acylation at room temperature

Over the past few decades, an impressive array of C-H activation methodology has been developed for organic synthesis. However, due to the inherent inertness of the C-H bonds (e.g. ∼110 kcal mol^-1 for the cleavage of C(aryl)-H bonds) harsh reaction conditions have been realized to overcome high energetic transition states resulting in a limited substrate scope and functional group tolerance. Therefore, the development of mild C-H functionalization protocols is in high demand to exploit the full potential of the C-H activation strategy in the synthesis of a complex molecular framework. Although, electron-rich substrates undergo electrophilic metalation under relatively mild conditions, electron-deficient substrates proceed through a rate-limiting C-H insertion under forcing conditions at high temperature. In addition, a stoichiometric amount of toxic silver salt is frequently used in palladium catalysis to facilitate the C-H activation process which is not acceptable from the environmental and industrial standpoint. We report herein, a Pd(ii)-catalyzed decarboxylative C-H acylation of 2-arylpyridines with α-ketocarboxylic acids under mild conditions. The present protocol does not require stoichiometric silver(i) salts as additives and proceeds smoothly at ambient temperature. A novel decarbonylative C-H acylation reaction has also been accomplished using aryl glyoxals as acyl surrogates. Finally, a practical C-H acylation via a dehydrogenative pathway has been demonstrated using commercially available benzaldehydes and aqueous hydroperoxides. We also disclose that acetonitrile solvent is optimal for the acylation reaction at room temperature and has a prominent role in the reaction outcome. Control experiments suggest that the acylation reaction via decarboxylative, decarbonylative and dehydrogenative proceeds through a radical pathway. Thus we disclose a practical protocol for the sp² C-H acylation reaction.

Recent developments in palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C–Z (Z = B, Si, Sn, S, N, C, H) bonds in bi(hetero)aryl synthesis

This review article describes the palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C_(Ar)–Z (Z = B, Si, Sn, S, N, C, H) bonds for facile bi(hetero)aryl synthesis in the past 10 years.

Transition-metal-free arylation of benzoxazoles with aryl nitriles

Transition-metal-free arylation of benzoxazoles with aryl nitriles has been developed to afford important 2-aryl benzoxazoles under simple reaction conditions.

Synthesis and C-H Functionalization Chemistry of Thiazole-Semicoronenediimides (TsCDIs) and -Coronenediimides (TCDIs)

Coronenediimide (CDI) derivatives have a planar structure, a reasonably high electron affinity, and a rigid and extended delocalized π-system. Therefore, this core and variants thereof may be promising building blocks for the synthesis of electron transport materials. Herein, we have synthesized thiazole-semicoronenediimides (TsCDIs) and -coronenediimides (TCDIs) by a two-step process from a perylenediimide (PDI) precursor. Conditions for C-H arylation and heteroarylation of the thiazole moiety of this core were developed and were successfully used for the synthesis of dimer, triad, and polymeric materials. The optical and electrochemical properties of these materials and their monomers were examined as a function of side-chain modification and π-extension. With their broad optical absorption and low reduction potentials, these materials could be candidates as organic semiconductors for applications in OFETs and as nonfullerene acceptors.

Transition-Metal-Free Decarboxylative Iodination: New Routes for Decarboxylative Oxidative Cross-Couplings

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.

Recent Progress in Decarboxylative Oxidative Cross-Coupling for Biaryl Synthesis

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.

Palladium-catalyzed regioselective C–H bond arylations at the C3 position of ortho-substituted fluorobenzenes

We report herein the palladium-catalyzed C–H bond arylation of fluorobenzene derivatives at the ortho-position to the fluorine atom. Bromo, chloro or methoxy substituents at the fluorobenzenyl ortho-position can be used to increase the reactivity of the C–H bond at the C3 position.

N-Iodosuccinimide involved one-pot metal-free synthesis of 2-heteroaromatic benzothiazole compounds

A metal-free and operationally simple protocol for the synthesis of structurally diverse 2-hetarylbenzothiazoles via oxidative condensation of the sp³ C–H bond with benzothiazoles has been described.