Ruthenium-Catalyzed Remote C–H Sulfonylation of N-Aryl-2-aminopyridines with Aromatic Sulfonyl Chlorides

Ruthenium-Catalyzed Difunctionalization of Vinyl Cyclopropanes for Double m-C(sp2)-H/C-5(sp3)-H Functionalization

With in-depth research on 1,2-difunctionalization, remote difunctionalization has garnered widespread attention for achieving multifunctionality. Herein, we report a strategy for achieving remote difunctionalization under mild conditions. This strategy exhibited good substrate suitability and functional group tolerance. In addition, the significance of this method is further evidenced by its successful application in scaling up and conducting additional transformations of target compounds. Mechanistic studies showed that a radical might be involved in this process.

Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C-H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C-H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience.

Ruthenium(II)-Catalyzed Remote C-H Sulfonylation of 2-Pyridones

Herein, a ruthenium-mediated remote C-H mono- and disulfonylation of 2-pyridones with arylsulfonyl chlorides is developed. The catalytic system consisting of a [Ru(p-cymene)Cl2]2 catalyst and KOAc additive allows 2-pyridones to undergo C3,C5-disulfonylation in 1,4-dioxane, and C5-sulfonylation when the C3-position of 2-pyridones is blocked. The successful transformation of the products and late-stage modification of estrone further highlighted the potential utility and significance of this synthetic protocol. Preliminary mechanistic studies indicated that the remote regioselectivity might be dictated via chelation-assisted ruthenation.

Direct C(3)5-H Polyfluoroarylation of 2-Amino/alkoxy Pyridines Enabled by a Transient and Electron-deficient Palladium Intermediate

Herein, we present an unprecedented azine-limited C5-H polyfluoroarylation of 2-aminopyridines enabled by a transient and electron-deficient perfluoroaryl-Pd species via C-H/C-H coupling. The protocol further allows C3(5)-H polyfluoroarylation of 2-alkoxypyridines guided by sterics and electronics for the first time. The late-stage C-H functionalization of drugs, drug derivatives, and natural product derivatives and synthesis of C5-aryl drug derivatives further demonstrated the method's utility. The preliminary mechanistic studies reveal that the synergistic combination of the bulky yet electrophilic perfluoroaryl-Pd species and the partial nucleophilicity of the C5-position of 2-amino/alkoxy-pyridines is the origin of reactivity and selectivity. Importantly, the first experimental evidence for the role of diisopropyl sulfide is provided.

C-H acylation of aniline derivatives with α-oxocarboxylic acids using ruthenium catalyst

An efficient and convenient synthetic strategy for ruthenium(II)-catalyzed ortho-acylation of N-(2-pyridyl)-anilines using α-oxycarboxylic acids as acyl sources is described. The procedure can smoothly proceed under mild conditions, showing good functional group tolerance. Valuable ortho-acylated aniline products have been obtained with moderate to good yields. Furthermore, the reaction could be easily scaled up to the gram scale.

A novel quinoline-based NNN-pincer Cu(II) complex as a superior catalyst for oxidative esterification of allylic C(sp3)-H bonds

We report for the first time that the quinoline-based NNN-pincer Cu(II) complex acts as an air stable superior catalyst for the oxidative cross-coupling of the allyl sp³ C-H bond with an acid for the synthesis of allyl esters in a homogeneous system at ambient temperature. The synthesized catalyst, 1, has been well characterized by various analytical techniques (HRMS, single crystal X-ray diffraction, CV, EPR, UV-vis spectroscopy) and showed excellent catalytic activity for the oxidative esterification of allylic C(sp³)-H bonds at 40 °C within a very short period of time (1 h) using only 1 mol% of the catalyst. A wide variety of aromatic allylic esters were synthesized in moderate to good yields, which could be extended to aliphatic allyl esters as well.

Ruthenium(II)-Catalyzed Chelation-Assisted Desulfitative Arylation of Benzo[h]quinolines with Arylsulfonyl Chlorides

Herein, a novel chelation-assisted C-H arylation reaction of benzo[h]quinoline is described. This transformation, using [RuCl₂(p-cymene)]₂ as the catalyst and cheap and easily accessible arylsulfonyl chlorides as the arylation source, featured simple reaction conditions, a broad substrate scope, and functional group tolerance. The successful application of some bioactive-molecule-based sulfonyl chlorides further highlighted the potential utility and importance of this desulfitative C-H arylation protocol.

Looking deep into C-H functionalization: the synthesis and application of cyclopentadienyl and related metal catalysts

Metal catalyzed C-H functionalization offers a versatile platform for methodology development and a wide variety of reactions now exist for the chemo- and site-selective functionalization of organic molecules. Cyclopentadienyl-metal (CpM) complexes of transition metals and their correlative analogues have found widespread application in this area, and herein we highlight several key applications of commonly used transition-metal Cp-type catalysts. In addition, an understanding of transition metal Cp-type catalyst synthesis is important, particularly where modifications to the catalyst structure are required for different applications, and a summary of this aspect is given.

Recyclable Aliphatic Nitrile-Template Enabled Remote meta-C-H Functionalization at Room Temperature

This article describes the development of a new aliphatic nitrile-template-directed remote meta-selective C-H olefin functionalization reaction of arenes. Remarkably, unlike the previous reports, this process is feasible at room temperature and enabled the formation of products with excellent regioselectivity. The present protocol encompasses a broad spectrum of substituted dihydrocinnamic acids and olefins, producing meta-C-H olefinated products (up to 96% yield). In addition, the efficacy of the present method has been showcased by the synthesis of various drug analogues (e.g., cholesterol, estrone, ibuprofen, and naproxen). Significantly, the robustness of meta-olefination was also demonstrated by gram-scale synthesis. The new nitrile-based meta-directing template, in particular, could be easily synthesized in two steps and recycled under mild conditions.

Selective C3–H nitration of 2-sulfanilamidopyridines with tert-butyl nitrite

A selective C3–H nitration of bioactive 2-sulfanilamidopyridine derivatives, including corticosteroid 11-β-dehydrogenase isozyme, secretory phospholipase A2 inhibitor and human neutrophil elastase inhibitor, has been reported.

Radical Cyclization of 1,n-Enynes and 1,n-Dienes for the Synthesis of 2-Pyrrolidone

2-Pyrrolidones have aroused enormous interest as a useful structural moiety in drug discovery; however, not only does their syntheses suffer from low selectivity and yield, but also it requires high catalyst loadings. The radical cyclization of 1,n-enynes and 1,n-dienes has demonstrated to be an attractive method for the synthesis of 2-pyrrolidones due to its mild reaction conditions, fewer steps, higher atom economy, excellent functional group compatibility, and high regioselectivity. Furthermore, radical receptors with unsaturated bonds (i. e. 1,n-enynes and 1,n-dienes) play a crucial role in realizing radical cyclization because of the ability to selectively introduce one or more radical sources. In this review, we discuss representative examples of methods involving the radical cyclization of 1,n-enynes and 1,n-dienes published in the last five years and discuss each prominent reaction design and mechanism, providing favorable tools for the synthesis of valuable 2-pyrrolidone for a variety of applications.

Iron-Catalyzed Remote C–H Alkylation of 8-Amidoquinolines with Cycloalkanes

An iron-catalyzed, peroxide-mediated cross-dehydrogenative coupling between 8-amidoquinolines and cycloalkanes has been developed for the site-selective alkylation of the quinoline nucleus at the C5 position. The reaction tolerates various substituted N-(quinolin-8-yl)benzamides and N-(quinolin-8-yl)alkylamides, affording the corresponding C5-alkylation products in good yields. On the basis of control experiments, a reaction mechanism involving the addition of an alkyl radical to an iron-chelated intermediate is proposed.

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

Silver-promoted oxidative sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates leading to dihydronaphthalene derivatives

Silver-promoted sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates is established for the construction of 1-sulfonylmethylated 3,4-dihydronaphthalenes. This sulfonylation process involves a radical pathway, including sulfonyl radical formation, radical addition, ring-opening and cyclization. The 1-sulfonylmethylated 3,4-dihydronaphthalenes can be converted into other useful products.

Palladium-catalyzed remote C-H functionalization of 2-aminopyrimidines

A straightforward strategy was developed for the arylation and olefination at the C5-position of the N-(alkyl)pyrimidin-2-amine core with readily available aryl halides and alkenes, respectively. This approach was highly regioselective, and the transformation was achieved based on two different (Pd(ii)/Pd(iv)) and (Pd(0)/Pd(ii)) catalytic cycles.

Ruthenium-catalyzed synthesis of indole derivatives from N-aryl-2-aminopyridines and alpha-carbonyl sulfoxonium ylides

Indole is a ubiquitous structural motif with important applications in many areas of chemistry. Given this, a simple and efficient Ru(ii)-catalyzed synthesis of indole via intermolecular annulation of N-aryl-2-aminopyridines and sulfoxonium ylides was proposed and accomplished. Excellent selectivity and good functional group tolerance of this transformation were observed. This protocol provides easy access to a wide variety of useful indoles in the presence of a commercially available [Ru(p-cymene)Cl2]2 catalyst. A possible mechanism for the reaction pathway was also proposed. More importantly, this reaction will offer a useful method for the construction of enantioenriched indole frameworks.

Visible-light-mediated difunctionalization of vinylcyclopropanes for the synthesis of 1-sulfonylmethyl-3,4-dihydronaphthalenes

An efficient method for the visible-light-mediated sulfonylation/arylation of the C–C σ-bond in vinylcyclopropanes with sulfonyl chlorides to synthesize 1-sulfonylmethyl-substituted 3,4-dihydronaphalenes has been developed.

Ruthenium-catalyzed remote C5-sulfonation of N-alkyl-8-aminoquinolines

Ruthenium-catalyzed remote C–H sulfonation of 8-aminoquinolines with single C5-selectivity.

Transition metal catalysed C7 and ortho-selective halogenation of 2-arylbenzo[d]oxazoles

An approach to construct C–X bonds on the C7 or ortho-position of 2-arylbenzo[d]oxazoles by Rh and Ru catalysts has been reported.

Ruthenium(ii)-catalyzed remote C–H addition of 8 aminoquinoline amide to activated aldehyde

Remote C–H addition of 8-aminoquinoline amides at C-5 position to activated aldehydes have been developed using Ru(ii)-catalyst.

Remote alkylation of N-(quinolin-8-yl)benzamides with alkyl bromides via ruthenium(ii)-catalyzed C–H bond activation

A ruthenium(ii) catalyzed remote C-5 alkylation of the quinoline ring of N-(quinolin-8-yl)benzamides with alkyl bromides via C–H bond activation is described.