Rh(III)-Catalyzed C7-Alkylation of Isatogens with Malonic Acid Diazoesters

Rh(III)-catalyzed C7-alkylation of isatogens (indolin-3-one N-oxides) with malonic acid diazoesters has been developed. This strategy utilizes oxygen anion on the N-oxide group of isatogens as a directing group and successfully achieves the synthesis of a series of C7-alkylated isatogens with moderate to good yields (48-86% yields). Moreover, the N-oxides of isatogens can not only serve as the simple directing group for C7-H bond cleavage but also be deoxidized for easy removal.

Iridium catalysed C2 site-selective methylation of indoles using a pivaloyl directing group through weak chelation-assistance

Here we present an iridium catalysed C2-selective methylation of indoles using methyltrifluoroborate as a source of methyl group. The iridium catalyst selectively discriminates the indole C2 and C4 C-H bonds by coordination with a pivaloyl directing group.

Recent advances in theoretical studies on transition-metal-catalyzed regioselective C-H functionalization of indoles

Indole compounds are widely found in natural products and drug candidates. The transition-metal-catalyzed regioselective C-H bond functionalization of indoles as the most efficient method for the synthesis of various functionalized indoles has been extensively studied in the past two decades due to its advantages of step economy and atom economy. In general, the catalysts included the transition-metals (Pd, Rh, Ru, Cu, Co, Fe, Zn, and Ga) and these reactions were accomplished with a remarkably wide range of coupling reagents for construction of various C-C and C-X (X = N, O, S) bonds. However, the general and important rules of the regioselectivity are not clear to date. Therefore, a comprehensive analysis through previous reported theoretical studies on transition-metal-catalyzed regioselective C-H bond functionalization of indoles was crucial and significant. In this review, we found that when the C-H bond activation process was the rate-determining step, the regioselectivity ordinarily occurred at the C7 or C4 positions (on benzene ring), and otherwise, the regioselectivity often occurred at C2 position (on pyrrole ring). For indoline substrates, the C-H bond functionalization occurred at the benzene ring. General rules of the regioselectivities for transition-metal-catalyzed C-H bond functionalization of indoles. This review collects major advances in the transition-metal-catalyzed C-H bond functionalization of indoles and indolines.

Distinct Roles of Ag(I) and Cu(II) as Cocatalysts in Achieving Positional-Selective C-H Alkenylation of Isoxazoles: A Theoretical Investigation

For C-H alkenylation of aryl-substituted diarylisoxazoles, one mode is N-directed C-H alkenylation and the other is C-H alkenylation in the isoxazole ring. In this study, selective C-H alkenylations of 3,5-diarylisoxazoles have been investigated theoretically with the aid of density functional theory (DFT) calculations. With Cp*Rh^III as the catalyst, the N-directed C-H alkenylation is preferred as a result of the stronger interaction energy caused by the nitrogen-directing effect. With Pd(OAc)₂ as the catalyst and Ag₂CO₃ as the cocatalyst, their combination switches the regioselectivity to the C-H alkenylation in the isoxazole ring. The strong structural distortion involved in the competing N-directed olefin insertion transition state was found to suppress N-directed C-H alkenylation. With Pd(OAc)₂ as the catalyst and Cu(OTf)₂ as the cocatalyst, the N-directed C-H alkenylation becomes preferred due to the strong coordination of the nitrogen atom to the copper center. In particular, the structural and mechanistic information involved in the above two heterodimetallic Pd/Ag and Pd/Cu catalytic systems will help toward understanding and designing novel relevant heterodimetallic-catalyzed reactions.

Nickel-catalyzed hydroalkenylation of styrene with phenylpropanal: theoretical studies on the mechanism, regioselectivity, and role of phenylboronic acid

The effects of different solvents, Brønsted acids, and ligands on reactivity are clarified through our calculations.

Cp*Co(III)-Catalyzed Regioselective C2 Amidation of Indoles Using Acyl Azides

A cobalt-catalyzed C2-selective amidation of indoles using acyl azides has been accomplished. Isotope experiments suggest that C-H activation is reversible. The use of sustainable Co catalysis, functional group diversity, substrate scope, and regioselectivity are the important practical features.

Metal-free oxidative trifluoromethylation of indoles with CF3SO2Na on the C2 position

An efficient method of synthesizing 2-trifluoromethylindoles from indoles with easy-to-handle, cheap and low-toxic CF₃SO₂Na under metal-free conditions is described, which selectively introduces trifluoromethyl to indoles on the C2 position. The desired product can be obtained in 0.7 g yield. A radical intermediate may be involved in this transformation.

An efficient method of synthesizing 2-trifluoromethylindoles from indoles with easy-to-handle, cheap and low-toxic CF₃SO₂Na under metal-free conditions is described, which selectively introduces trifluoromethyl to indoles on the C2 position.

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.

Catalyst-controlled positional-selectivity in C–H functionalizations

C–H bonds are ubiquitous in organic molecules and typically these bonds are chemically indistinct from each other and it would be highly advantageous for a synthetic chemist to have the ability to choose which C–H bond is functionalized in a given molecule.