Copper-Catalyzed Synthesis of 3-Aryl-9H-imidazo[1,5-a]indol-9-ones Using Oxygen as the Sole Oxidant

A three-component strategy was developed for 3-phenyl-9H-imidazo[1,5-a]indol-9-one preparation from indole-2-carboxaldehydes, aromatic aldehydes, and ammonium acetate under copper catalysis conditions. In this process, a new five-membered ring was formed and the C3 position in the indole substrate was selectively oxidized into a ketone skeleton using oxygen as the sole oxidant and ammonium acetate as the nitrogen source. Furthermore, same products also could be achieved from indole-2-carboxaldehydes and benzyl amines under similar reaction conditions.

Palladium-Catalyzed Directed Aldehyde C-H Arylation of Quinoline-8-carbaldehydes: Exploring the Reactivity Differences between Aryl (Pseudo) Halides

We have developed a method for Pd-catalyzed direct C-H arylation of quinoline-8-carbaldehydes with either aryl iodides or aryl diazonium salts for the synthesis of aryl quinolinyl ketones. Aryl iodide substituted with an electron-donating group favors the reaction, whereas aryl diazonium salt substituted with an electron-withdrawing group showed excellent reactivity. A range of aryl quinolinyl ketones were synthesized in good-to-excellent yields, with very good functional group tolerance. Our methodology was successfully applied to synthesize highly potent tubulin polymerization inhibitors and can be easily scaled up to a gram scale.

Recent advances in the synthesis of pyrrolo[1,2-a]indoles and their derivatives

The pyrrolo[1,2-a]indole unit is a privileged heterocycle found in numerous natural products and has been shown to exhibit diverse pharmacological properties. Thus, recent years have witnessed immense interest from the synthesis community on the synthesis of this scaffold. In light of the ever-increasing demand for pyrrolo[1,2-a]indoles in drug discovery, this review provides an overview of recent synthesis methods for the preparation of pyrrolo[1,2-a]indoles and their derivatives. The mechanistic pathway and stereo-electronic factors affecting the yield and selectivity of the product are briefly explained. Furthermore, we have attempted to demonstrate the utility of the developed methods in the synthesis of bioactive molecules and natural products, wherever offered.

Acylation of Arenes with Aldehydes through Dual C-H Activations by Merging Photocatalysis and Palladium Catalysis

An acylation of arenes with aldehydes through dual C-H activations at room temperature is reported. The acylation was initiated by phenanthraquinone-catalyzed hydrogen atom transfer from aldehyde under visible light irradiation. The aldehyde-derived acyl radical merged with palladium-catalyzed activation of arenes to afford the cross coupling products.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Palladium-catalyzed decarboxylative, decarbonylative and dehydrogenative C(sp2)-H acylation at room temperature

Over the past few decades, an impressive array of C-H activation methodology has been developed for organic synthesis. However, due to the inherent inertness of the C-H bonds (e.g. ∼110 kcal mol^-1 for the cleavage of C(aryl)-H bonds) harsh reaction conditions have been realized to overcome high energetic transition states resulting in a limited substrate scope and functional group tolerance. Therefore, the development of mild C-H functionalization protocols is in high demand to exploit the full potential of the C-H activation strategy in the synthesis of a complex molecular framework. Although, electron-rich substrates undergo electrophilic metalation under relatively mild conditions, electron-deficient substrates proceed through a rate-limiting C-H insertion under forcing conditions at high temperature. In addition, a stoichiometric amount of toxic silver salt is frequently used in palladium catalysis to facilitate the C-H activation process which is not acceptable from the environmental and industrial standpoint. We report herein, a Pd(ii)-catalyzed decarboxylative C-H acylation of 2-arylpyridines with α-ketocarboxylic acids under mild conditions. The present protocol does not require stoichiometric silver(i) salts as additives and proceeds smoothly at ambient temperature. A novel decarbonylative C-H acylation reaction has also been accomplished using aryl glyoxals as acyl surrogates. Finally, a practical C-H acylation via a dehydrogenative pathway has been demonstrated using commercially available benzaldehydes and aqueous hydroperoxides. We also disclose that acetonitrile solvent is optimal for the acylation reaction at room temperature and has a prominent role in the reaction outcome. Control experiments suggest that the acylation reaction via decarboxylative, decarbonylative and dehydrogenative proceeds through a radical pathway. Thus we disclose a practical protocol for the sp² C-H acylation reaction.

Electrochemical recognition of alkylimidazolium-mediated ultrafast charge transfer on graphene surfaces

The charge transfer and active sites of metal-free imidazolium-based composites were unveiled by an electrochemical method with high sensitivity and selectivity due to the specific donor–acceptor coupling of imidazolium with NO₂⁻.

Pd-Catalyzed C(sp2)–H aminocarbonylation using the Langlois reagent as a carbonyl source

An efficient Pd-catalyzed C(sp²)–H aminocarbonylation of aryl carboxamides assisted by an N,S-bidentate directing group was developed.

Selective formation of phthalimides from amines, aldehydes and CO by Pd-catalyzed oxidative C–H aminocarbonylation

The Pd/Cu-catalyzed intramolecular C–H bond aminocarbonylation utilizing imines as the amine source has been developed. This transformation provides an efficient and straightforward protocol for the synthesis of phthalimides which widely exist in natural products, pharmaceutical and functional materials. Various functional groups are tolerated and the yields are up to 99%.