Chemodivergent assembly of ortho-functionalized phenols with tunable selectivity via rhodium(III)-catalyzed and solvent-controlled C-H activation

Synthesis of 2-Hydroxycarbazoles via Rh(III)-Catalyzed Cascade Cyclization of Indolyl Nitrones with Alkylidenecyclopropanes

The synthesis of functionalized carbazoles is an important tool in the discovery of bioactive molecules. Herein, we present a method for synthesizing 2-hydroxycarbazoles from indolyl nitrones and alkylidenecyclopropanes under Rh(III) catalysis. A notable reaction pathway involves [3 + 2] cycloaddition between indolyl nitrones and diene intermediates, followed by aromatization and reductive N-O bond cleavage in a cascade manner. Moreover, a series of post-transformations highlights the utility of the proposed method.

Base-controlled regio-divergent C-H bond functionalization

The choice of appropriate directing groups, catalysts, ligands, bases, and solvents to give different regioisomers from the same precursors can improve the efficiency and atom economy in synthetic organic chemistry, while minimizing costs and expanding know chemical space. Base-controlled regio-divergent C-H bond functionalization is an important control strategy in organic synthesis, with the advantages of being operationally simple, and using cheap and available bases with low-toxicity that are easily separable. This highlight is classified into three sections: base-controlled, base-controlled transition metal-catalysed and base-controlled photocatalytic regio-divergent C-H bond functionalization. By summarizing the C-H bond activation model, the mechanisms underlying the regio-divergence and the influencing factors, this highlight aims to deepen the understanding of selective C-H bond functionalization at a molecular level. We expect that this highlight article will provide valuable information for understanding the mechanism of C-H bond functionalization, whilst providing a reference for developing green, efficient C-H bond transformation strategies.

Diastereoselective Synthesis of Cyclobutanes via Rh-Catalyzed Unprecedented C-C Bond Cleavage of Alkylidenecyclopropanes

The stereoselective synthesis of highly substituted cyclobutanes is essential for the development of lead candidates in drug discovery. Herein, we present a novel Rh(III)-catalyzed reaction pathway for synthesizing substituted cyclobutanes, which involves a concerted N-C bond formation and C-C bond cleavage between 2-aryl quinazolinones and alkylidenecyclopropanes. Notably, the combination of Rh(III) catalyst and HFIP solvent plays a critical role in facilitating the formation of cyclobutane rings.

Solvent Dictated Organic Transformations

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage. The solvent helps the reaction profile both chemically and energetically to reach the targeted product. Organic transformations via C-H activation from the solvent assistance perspective has been discussed in this review. Various solvents such as tetrahydrofuran (THF), MeCN, dichloromethane (DCM), dimethoxyethane (DME), 1,2-dichloroethane (1,2-DCE), dimethylformamide (DMF), dimethylsulfoxide (DMSO), isopropyl nitrile (iPrCN), 1,4-dioxane, AcOH, trifluoroacetic acid (TFA), Ac2O, PhCF3, chloroform (CHCl3), H2O, N-methylpyrrolidone (NMP), acetone, methyl tert-butyl ether (MTBE), toluene, p-xylene, alcohols, MeOH, 1,1,1-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), tert-amyl alcohol and their roles are discussed. The exclusive role of the solvent in various transformations has been deliberated by highlighting the substrate scope, along with the proposed mechanisms. For easy classification, the review has been divided into three parts: (i) solvent-switched divergent C-H activation; (ii) C-H bond activation with solvent as the coupling reagent, and (iii) C-H activation with solvent caging and solvent-assisted electron donor acceptor (EDA) complex formation and autocatalysis.

Development of novel transition metal-catalyzed synthetic approaches for the synthesis of a dihydrobenzofuran nucleus: a review

The synthesis of dihydrobenzofuran scaffolds bears pivotal significance in the field of medicinal chemistry and organic synthesis. These heterocyclic scaffolds hold immense prospects owing to their significant pharmaceutical applications as they are extensively employed as essential precursors for constructing complex organic frameworks. Their versatility and importance make them an interesting subject of study for researchers in the scientific community. While exploring their synthesis, researchers have unveiled various novel and efficient pathways for assembling the dihydrobenzofuran core. In the wake of extensive data being continuously reported each year, we have outlined the recent updates (post 2020) on novel methodological accomplishments employing the efficient catalytic role of several transition metals to forge dihydrobenzofuran functionalities.

Chemodivergent Photocatalyzed Heterocyclization of Hydrazones and Isothiocyanates for the Selectivity Synthesis of 2-Amino-1,3,4-thiadiazoles and 1,2,4-Triazole-3-thiones

A photocatalytic chemodivergent reaction for the selectivity formation of C-S and C-N bonds in a controlled manner was proposed. The reaction medium, either neutral or acidic, is critical to dictate the formation of 2-amino-1,3,4-thiadiazoles and 1,2,4-triazole-3-thiones from isothiocyanates and hydrazones. This is a practical protocol to achieve the chemoselectivity under mild and metal-free conditions.

Rh(III)-Catalyzed chemo-, regio- and stereoselective carboamination of sulfonyl allenes with N-phenoxy amides or N-enoxy imides

The Rh(III)-catalyzed chemo-, regio- and stereoselective carboamination of sulfonyl allenes has been realized by virtue of either N-phenoxy amides or N-enoxy imides simultaneously acting as the C- and N-sources, via redox-neutral tandem C-H activation/allene insertion/oxidative addition/C-N bond formation for the direct construction of allylamine derivatives equipped with an α-quaternary carbon center. This protocol features high atom-economy with good substrate compatibility and exhibits profound synthetic potential for late-stage C-H modification of complex molecules.

Site-selective rhodium carbene transfer of 2 hydroxy-β-nitrostyrenes with diazo compounds En route to 2-alkylated benzofurans

The Rh(iii)-catalysed cascade vinylic C–H functionalization/carbene transfer/Michael addition sequence of 2-hydroxy-β-nitrostyrenes has been realized, delivering the 2-alkylated benzofuran derivatives as potential tyrosinase inhibitors.

Specific assembly of dihydrobenzofuran frameworks via Rh(iii)-catalysed C–H coupling of N-phenoxyacetamides with 2-alkenylphenols

The synergistic dual directing group-enabled and Rh(iii)-catalysed redox-neutral C–H functionalization/[3+2] annulation has been realized for the synthesis of dihydrobenzofurans.