Nickel Catalyzed Aryl-Aryl Bridging C-N Bond Activation of 2-Pyridylpyridones and 6-Purinylpyridones.

A Ni-catalyzed C-N bond activation of 2-pyridylpyridone and 1-(9-alkyl 9-purin-6-yl)pyridin-2(1)-one and coupling with arylboronic acid have been achieved. A unique feature of this reaction is the strategic activation of the bridging C-N bond and replacement of the pyridone unit with aryl groups using nickel catalyzed Suzuki-Miyaura coupling. This provides an exciting new tool to build C-C bonds in the place of pyridones.

Rhodium-Catalyzed Synthesis of 2-Methylindoles via C-N Bond Cleavage of -Allylbenzimidazole.

A rhodium-catalyzed oxidative C-H/N-H dehydrogenative [3 + 2] annulation strategy has been reported between anilines and -allylbenzimidazole for the synthesis of 2-methylindole scaffolds. An -allylbenzimidazole has been used as a 2C synthon for the synthesis of indole, and more importantly, this transformation involves the cleavage of the thermodynamically stable C-N bond of allylamine. Detailed mechanistic studies have been performed and a key intermediate was detected in HRMS.

-Allylbenzimidazole as a strategic surrogate in Rh-catalyzed stereoselective -propenylation of aryl C(sp)-H bond.

A Rh-catalyzed C(sp)-H propenylation has been reported by taking -allyl benzimidazole as an allylamine congener. This transformation has been observed for the first time, where a tandem process of C-H allylation followed by alkene isomerization delivers a highly stereoselective -propenylated product. Detailed mechanistic studies including the characterization of rhodacycle-intermediates have been conducted to understand the mechanism.

Co(II)-Catalyzed C-H/N-H Annulation of Cyclic Alkenes with Indole-2-carboxamides at Room Temperature: One-Step Access to β-Carboline-1-one Derivatives.

We report herein a cobalt-catalyzed 8-aminoquinoline-directed highly regio- and stereoselective C-H/N-H activation annulation of indole-2-carboxamides with 1,2-dihydronaphthalene for the synthesis of β-carboline-1-one derivatives at room temperature. A cheaper and commercially available cobalt catalyst has been used for this transformation. The protocol tolerates a wide range of functionalities, affording β-carboline-1-one derivatives in good yields.

Cobalt(III)-Catalyzed C-6 Alkenylation of 2-Pyridones by Using Terminal Alkyne with High Regioselectivity.

Co(III)-catalyzed alkenylation of 2-pyridones by using terminal alkyne as a reaction partner with high regioselectivity has been demonstrated for the first time. The reaction conditions are mild and compatible with a wide range of substrate combinations. It also shows good functional group tolerance.

O-Directed C-H functionalization via cobaltacycles: a sustainable approach for C-C and C-heteroatom bond formations.

This review focuses on providing comprehensive highlights of the recent advances in the field of cobalt-catalysed C-H functionalization and related synthetic concepts, relying on these through oxygen atom coordination. In recent years, 3d transition metal (Fe, Co, Cu & Ni) catalysed C-H functionalization reactions have received immense attention on account of its higher abundance and low cost, as compared to noble metals such as Ir, Rh, Ru and Pd. Among the first-row transition metals, cobalt is one of the extensively used metals for sustainable synthesis due to its unique reactivity towards the functionalization of inert C-H bonds.

Palladium-Catalyzed C-C Bond Activation of Cyclopropenone: Modular Access to Trisubstituted -Unsaturated Esters and Amides.

Strain-driven palladium/-heterocyclic carbene-catalyzed C-C bond activation of diphenylcyclopropenone (DPC) has been explored for one-step access to trisubstituted α,β-unsaturated esters and amides. The designed transformation works under mild conditions providing exclusively a single stereoisomer. Mechanistic studies support the oxidative addition of the C-C bond of cyclopropenone to in-situ-generated Pd(0) intermediate.

Rhodium-Catalyzed One-Pot Access to N-Polycyclic Aromatic Hydrocarbons from Aryl Ketones through Triple C-H Bond Activations.

A Rh-catalyzed pot and step economic synthesis of aza-polycyclic aromatic hydrocarbons (N-PAHs) from readily available aryl ketones and alkynes has been disclosed. Additionally, a novel synthetic application of the well-known aminating reagent hydroxylamine--sulfonic acid (HOSA) has been explored as an in situ redox-neutral directing group for the formation of N-PAHs via isoquinoline. Multiple bond formation in a single operation through a cascade of triple C-H bond activations is the beauty of this protocol.

Cobalt-Catalyzed One-Step Access to Pyroquilon and C-7 Alkenylation of Indoline with Activated Alkenes Using Weakly Coordinating Functional Groups.

A new strategy for the C(7)-H functionalization of indoline derivatives using first-row transition-metal cobalt has been demonstrated wherein the pivaloyl group acts as a weakly coordinating directing group. Biologically important pyroquilon (tetrahydropyroquinolinone) derivatives have been synthesized in a one-pot manner through selective C(7)-H functionalization and concomitant cyclization. In this process, aromatic C-H and amidic C-N bonds are cleaved, and new C-C and C-N bonds are formed in a step-economical fashion.