Ruthenium-Catalyzed meta -CAr -H Bond Difluoroalkylation of 2-Phenoxypyridines

meta-Allylation of Arenes via Ruthenium-Catalyzed Cross-Dehydrogenative Coupling

A successful example of oxidative meta-dehydrogenative allylation of arenes with alkenes has been developed using Ru(PPh₃)₃Cl₂ as a catalyst and DTBP as an oxidant. In the allylation process, pyrimidines, pyrazoles, and purines, found widely in nucleosides, were effective auxiliary groups. Gram-scale experiments took place smoothly under optimized conditions. Mechanistic studies indicated that ruthenium-catalyzed meta-dehydrogenative allylation was a free-radical process. The allylation process developed herein provides an efficient and practical strategy to prepare versatile meta-allylated arenes.

Ruthenium-catalyzed meta-difluoromethylation of arene phosphines enabled by 1,3-dione

A highly efficient, meta-selective difluoromethylation of arene phosphines has been developed with ruthenium catalysis using 1,3-dione as an effective ligand.

Recent advances in transition-metal catalyzed directed C–H functionalization with fluorinated building blocks

This review focuses on the advances in transition-metal catalyzed reactions with fluorinated building blocks via directed C–H bond activation for the construction of diverse organic molecules with an insight into the probable mechanistic pathway.

Toolbox for Distal C-H Bond Functionalizations in Organic Molecules

Transition metal catalyzed C-H activation has developed a contemporary approach to the omnipresent area of retrosynthetic disconnection. Scientific researchers have been tempted to take the help of this methodology to plan their synthetic discourses. This paradigm shift has helped in the development of industrial units as well, making the synthesis of natural products and pharmaceutical drugs step-economical. In the vast zone of C-H bond activation, the functionalization of proximal C-H bonds has gained utmost popularity. Unlike the activation of proximal C-H bonds, the distal C-H functionalization is more strenuous and requires distinctly specialized techniques. In this review, we have compiled various methods adopted to functionalize distal C-H bonds, mechanistic insights within each of these procedures, and the scope of the methodology. With this review, we give a complete overview of the expeditious progress the distal C-H activation has made in the field of synthetic organic chemistry while also highlighting its pitfalls, thus leaving the field open for further synthetic modifications.

Remote C–H Functionalizations by Ruthenium Catalysis

Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences, and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we discuss important mechanistic insights by experiments and computation, illustrating the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.

1 Introduction

2 Stoichiometric Remote C–H Functionalizations

3 meta-C–H Functionalizations

4 para-C–H Functionalizations

5 meta-/ortho-C–H Difunctionalizations

6 Conclusions

Iron-Catalyzed Highly para-Selective Difluoromethylation of Arenes

Direct functionalization of a C-H bond at either the meta or para position by only changing the catalyst system poses a significant challenge. We herein report the [Fe(TPP)Cl]-enabled, selective, C-H difluoromethylation of arenes using BrCF₂CO₂Et as the difluoromethylation source, which successfully altered the selectivity from the meta to the para position. A preliminary mechanistic study revealed the iron porphyrin complex not only activated the aromatic ring but also induced para selectivity due to the influence of ligand sterics.

Ruthenium-Catalyzed Meta-Selective C-H Difluoromethylation of Phenol Derivatives

With pyrimidine as the directing group, we achieved the meta-selective difluoromethylation of phenol derivatives using ruthenium as a catalyst. This synthetic scheme provided an efficient method for the syntheses of fluorine-containing phenol derivatives. A wide variety of phenol derivatives were well-suited, affording the corresponding products in moderate-to-good yields.

Regiodivergent C-H and Decarboxylative C-C Alkylation by Ruthenium Catalysis: ortho versus meta Position-Selectivity

Ruthenium(II)biscarboxylate complexes enabled the selective alkylation of C-H and C-C bonds at the ortho- or meta-position. ortho-C-H Alkylations were achieved with 4-, 5- as well as 6-membered halocycloalkanes. Furthermore, the judicious choice of the directing group allowed for a full control of ortho-/meta-selectivities. Detailed mechanistic studies by experiment and computation were performed and provided strong support for an oxidative addition/reductive elimination process for ortho-alkylations, while a homolytic C-X cleavage was operative for the meta-selective transformations.

A directing group-assisted ruthenium-catalyzed approach to access meta-nitrated phenols

meta-Selective C–H nitration of phenol derivatives was developed using a Ru-catalyzed σ-activation strategy. Cu(NO₃)₂·3H₂O was employed as the nitrating source, whereas Ru₃(CO)₁₂ was found to be the most suitable metal catalyst for the protocol.

Promising reagents for difluoroalkylation

This review describes recent advances in difluoroalkylation reactions using different substrates.