Rh(III)-Catalyzed C–H Functionalization of Indolines with Readily Accessible Amidating Reagent: Synthesis and Anticancer Evaluation

Pd-Catalyzed Direct C7 Trifluoromethylation of Indolines with Umemoto's Reagent

An efficient palladium-catalyzed region-selective C7-trifluoromethylation of indolines using commercially available Umemoto's reagent was reported. The reaction utilizing Umemoto's reagent as CF3 radical precursor, pyrimidine as a removable directing group, Pd(II) as a catalyst, and Cu(II) as an oxidant furnished the required products with excellent regioselectivities and good yields. The present strategy has good region-selectivity, broad substrate scope, and scale-up application. Additionally, the present method was underlined by the direct C-1 trifluoromethylation of carbazoles. Furthermore, C7 trifluoromethylated indole can also be easily obtained via Pd-catalyzed direct C-7 trifluoromethylation/oxidation/deprotection sequential reactions.

The eco-friendly electrosynthesis of trifluoromethylated spirocyclic indolines and their anticancer activity

A method for the electrochemical diastereoselective oxytrifluoromethylation of indoles was developed for the eco-friendly synthesis of CF₃-containing spirocyclic indolines. The cascade reaction comprised anodic oxidation to obtain CF₃ radicals, the addition of radicals to indoles, and intramolecular spirocyclization. The reaction system without external chemical oxidants could easily be scaled up. Antiproliferation assays of these CF₃-substituted spirocyclic indolines exhibited their promising activities and selectivities toward several types of cancer cells, including Huh-7, A549, and cisplatin-resistant cancer cells (A549/DDP).

Pd-Catalyzed C-H Halogenation of Indolines and Tetrahydroquinolines with Removable Directing Group

Pd-catalyzed directing-group-assisted regioselective halogenations to C7 of indolines and C8 of tetrahydroquinolines were achieved in good to excellent yields. The practicality and utility of the developed method have been illustrated by various functional group transformations such as arylation, alkenylation, cyanation, and silylation utilizing the installed synthetic handle. The concise synthesis of primaquine, an antimalarial drug, and formal syntheses of two bioactive natural products, hippadine and pratosine, have also been demonstrated.

Synthesis of Lactams via Ir-Catalyzed C-H Amidation Involving Ir-Nitrene Intermediates

x-membered lactams were synthesized via either an amidation of sp³ C-H bonds or an electrophilic substitution of arenes via Ir-nitrene intermediates. With the employment of a readily available iridium catalyst in dichloromethane or hexafluoro-2-propanol, a wide range of lactams were synthesized in good to excellent yields with high selectivity.

Rhodium(iii)-catalyzed ortho-C-H amidation of 2-arylindazoles with a dioxazolone as an amidating reagent

A simple and efficient method for the directed amidation of a wide range of 2-arylindazoles has been established for the first time through a rhodium-catalyzed C-H activation reaction with alkyl, aryl and heteroaryl dioxazolones. A series of N-(2-(2H-indazol-2-yl)phenyl)acetamide derivatives were synthesized in excellent yields. A mechanistic study was conducted to describe C-H bond cleavage which is likely to be involved in the rate determining step.

Cu(II)-Mediated Cross-Dehydrogenative Coupling of Indolines with Sulfonamides, Carboxamides, and Amines

A facile and efficient Cu-mediated protocol for the cross-dehydrogenative coupling of indoline with sulfonamides, carboxamides, and anilines is reported. The reaction takes place through Cu-mediated C7-H activation via a 6-membered metallacycle to afford the amide and amine derivatives in good yields with a wide range of functional group tolerance. The importance of the protocol has been demonstrated by synthesizing the antiproliferative agent, ER-67836.

Rhodium(III)-Catalyzed Regioselective C(sp2)-H Functionalization of 7-Arylpyrazolo[1,5-a]pyrimidines with Dioxazolones as Amidating Agents

Rh(III)-catalyzed C-H functionalization of 7-arylpyrazolo[1,5-a]pyrimidines was developed wherein the pyrazolo[1,5-a]pyrimidine moiety is reported for the first time to direct the C-H bond activation. Various 7-arylpyrazolo[1,5-a]pyrimidines underwent smooth C-H amidation with alkyl-, aryl-, and heteroaryl-substituted dioxazolones to afford the products in moderate to good yields. Mechanistic studies suggest that a six-membered rhodacycle intermediate involving N1 might play a key role in the regioselective catalytic cycle.

Rh(iii)-catalyzed C-7 arylation of indolines with arylsilanes via C-H activation

Site-selective synthesis of C-7 arylated indolines has been achieved via oxidative arylation of indolines with arylsilanes under Rh(iii)-catalyzed C-H activation of indolines by using CuSO4 as a co-oxidant. This transformation has been explored for a wide range of substrates under mild conditions.

Ru(ii)-Catalyzed C7-acyloxylation of indolines with carboxylic acids

Ruthenium(ii)-catalyzed site-selective C7-acyloxylation of indolines with carboxylic acids is presented. The substrate scope and functional group tolerance are important practical features. The kinetic isotope studies suggest that C-H bond activation may be the rate-determining step.

Transition-metal-catalyzed site-selective C7-functionalization of indoles: advancement and future prospects

The advancement and future prospects of transition-metal-catalyzed auxiliary assisted regioselective C7-functionalization of indoles/indolines are covered in this article.

Recent Progress on Cyclic Nitrenoid Precursors in Transition-Metal-Catalyzed Nitrene-Transfer Reactions

Nitrene-transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene-transfer reactions has been dominantly supported not only by improvements in transition-metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen-containing compounds was reported, a new approach using various N-heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene-transfer chemistry from the viewpoint of its precursors. In particular, the use of N-heterocycles such as 2H-azirines, 1,4,2-dioxazol-5-ones, 1,2,4-oxadiazol-5-ones, isoxazol-5(4H)-ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry.

Ruthenium(II)-Catalyzed Regioselective C-8 Hydroxylation of 1,2,3,4-Tetrahydroquinolines

Ru(II)-catalyzed chelation-assisted highly regioselective C8-hydroxylation of 1,2,3,4-tretrahydroquinolines has been developed. Various 1,2,3,4-tetrahydroquinolines underwent smooth C8-H hydroxylation with cheap and safe K₂S₂O₈ as the oxidant and oxygen source to furnish the corresponding products in good to excellent yields with high tolerance of the functional groups. The choice of a readily installable and removable N-pyrimidyl directing group is the key to catalysis. Mechanistic studies suggest the involvement of a six-membered ruthenacycle intermediate in the catalytic cycle. The method can also be extended to the direct hydroxylation of other (hetero)arene C-H bonds.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Synthesis of TMPA Derivatives through Sequential Ir(III)-Catalyzed C-H Alkylation and Their Antidiabetic Evaluation

The synthesis and antidiabetic evaluation of ethyl 2-[2,3,4-trimethoxy-6-(1-octanoyl)phenyl]acetate (TMPA) and its structural analogs are described. The construction of TMPA derivatives has been successfully achieved in only two steps, which involve the iridium(III)-catalyzed α-alkylation of acetophenones with alcohols and the ketone-directed iridium(III)- or rhodium(III)-catalyzed redox-neutral C-H alkylation of α-alkylated acetophenones using Meldrum's diazo compounds. This synthetic protocol efficiently provides a range of TMPA derivatives with site selectivity and functional group compatibility. In addition, the site-selective demethylation of TMPA derivative affords the naturally occurring phomopsin C in good yield. Moreover, all synthetic compounds were screened for in vitro adenosine 5'-monophosphate-activated protein kinase (AMPK) activation using HepG2 cells. Furthermore, TMPA (5ac) and 5cd showing the most potent AMPK activation were treated for the in vivo antidiabetic experiment. Notably, our synthetic compound 5cd was found to display the powerful antidiabetic effect, stronger than that of metformin and TMPA (5ac).

Rhodium(iii)-catalyzed directed amidation of unactivated C(sp3)–H bonds to afford 1,2-amino alcohol derivatives

A rhodium-catalyzed directed C(sp³)–H amidation to afford 1,2-amino alcohol oxime derivatives has been developed.

Rhodium-catalyzed C7-alkylation of indolines with maleimides

A rhodium(iii)-catalyzed direct cross-coupling reaction of indolines with maleimides via C–H bond activation was developed.

Cp*Rh(iii)-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one toward 2-aryl quinazolin-4(3H)-one derivatives

A [Cp*Rh^III]-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one was developed, affording a series of 2-aryl quinazolin-4(3H)-one derivatives.

Mechanistic insight into the C7-selective C–H functionalization of N-acyl indole catalyzed by a rhodium complex: a theoretical study

The role of the additive AgNTf₂ and the origins of the reaction are clarified through our calculations.

Gold-catalyzed C5-alkylation of indolines and sequential oxidative aromatization: access to C5-functionalized indoles

A novel protocol towards the rapid assembly of C5-alkylated indole derivatives has been developed via gold-catalyzed regioselective functionalization and subsequent oxidative aromatization.