Phthalazinone-Assisted C-H Amidation Using Dioxazolones Under Rh(III) Catalysis

Rhodium(III)-catalyzed C-H alkylation of arylhydrophthalazinediones with α-Cl ketones as sp3-carbon alkylated agents

A Rh(III)-catalyzed C-H bond direct alkylation between 2-arylphthalazine-1,4-diones and α-Cl ketones, which are sp³-carbon synthons, under mild conditions has been disclosed. The corresponding phthalazine derivatives are readily obtained in moderate to excellent yields with a wide range of substrates and high functional group tolerance. The practicality and utility of this method are demonstrated by the derivatization of the product.

Rhodium-Catalyzed Azine-Directed C-H Amidation with N-Methoxyamides

Using N-methoxyamide reagents as an amide source, C-H amidation was realized at the ortho position of azine under the action of rhodium and boric acid. The method has mild reaction conditions, high atomic utilization, excellent yield, and wide adaptability to amidation reagents (both aromatic amides and fatty amides are applicable). Amide-substituted ketones can be obtained by a simple treatment and can be further transformed into bioactive substances. This provides a good supplement for the C-H bond amidation of aromatic rings.

An Approach to Vinylidenequinazolines from Isoxazoles and Dioxazolones

An effective strategy for the synthesis of vinylidenequinazolines has been efficaciously developed, which involves Rh(III)-assisted C-H amidation followed by ring-opening and intramolecular annulation. This protocol shows a straightforward way to construct diverse quinazoline units with a wide functional group compatibility from readily available isoxazoles and dioxazolones.

Accessing oxy-functionalized N-heterocycles through rose bengal and TBHP integrated photoredox C(sp3)–O cross-coupling

A C(sp3)–O coupling strategy is described involving tautomerizable N-heterocycles (phthalazinone, pyridne, pyrimidinone and quinoxalinone) carbonyl employing rose bengal as the photocatalyst and TBHP.

Synthesis of π-Extended Heterocycles via Rh(III)-Catalyzed Oxidative Annulation of 5-Aryl Pyrazinones with Alkynes

The Rh(III)-catalyzed C-H functionalization and subsequent oxidative annulation between 5-aryl pyrazinones and internal alkynes are reported. This protocol provides facile access to a wide range of pyrazinone-linked naphthalenes via the C(sp²)-H alkenylation and subsequent annulation. This transformation is characterized by mild conditions, simplicity, and excellent functional group compatibility. Notably, it is a first report of the utilization of pyrazinones as directing groups in C-H functionalization.

Transition-metal-catalyzed C-H bond activation/functionalization and annulation of phthalazinones

Phthalazinones and their higher congeners are commonly prevalent structural motifs that occur in natural products, bioactive molecules, and pharmaceuticals. In the past few decades, transition-metal-catalyzed reactions have received an overwhelming response from organic chemists as challenging organics and heterocycles could be built with ease. Currently, the synthesis of phthalazinones largely depends on transition-metal catalysis, especially by palladium-catalyzed carbonylation. Further, the dominance of transition-metal catalysts was realized from the phthalazinones viewpoint, as nitrogen and oxygen atoms endowed upon them act as directing groups to facilitate diverse C-H activation/functionalization/annulation reactions. This highlight describes the various synthetic methods used to access phthalazinones and functionalize them by reacting with various coupling partners via chelation assistance strategy involving C(sp²)-H/N-H bond activation in the presence of transition-metal (Rh, Ru, Pd, and Ir) catalysts. The mechanisms of sulfonylation, halogenation, acylmethylation, alkylation, and annulation reactions are discussed.

Direct synthesis of indazole derivatives via Rh(III)-catalyzed C-H activation of phthalazinones and allenes

A novel Rh(III)-catalyzed annulation of phthalazinones or pyridazinones with various allenes was developed, leading to the formation of indazole derivatives bearing a quaternary carbon in moderate to good yields. The targeted products were synthesized via sequential C-H activation and olefin insertion, followed by β-hydride elimination and intramolecular cyclization. The synthetic protocol proceeded efficiently with broad functional group tolerance, high atom efficiency and high Z-selectivity. The practicability of this method was proved by synthetic transformation.

Enantioselective Catalytic C-H Amidations: An Highlight

The crucial role played by compounds bearing amide functions, not only in biological processes but also in several fields of chemistry, life polymers and material sciences, has brought about many significant discoveries and innovative approaches for their chemical synthesis. Indeed, a plethora of strategies has been developed to reach such moieties. Amides within chiral molecules are often associated with biological activity especially in life sciences and medicinal chemistry. In most of these cases, their synthesis requires extensive rethinking methodologies. In the very last years (2019–2020), enantioselective C-H functionalization has appeared as a straightforward alternative to reach chiral amides. Therein, an overview on these transformations within this timeframe is going to be given.

Rhodium-Catalyzed Directed C(sp2)-H Bond Addition of 2-Arylindazoles to N-Sulfonylformaldimines and Activated Aldehydes

Rhodium-catalyzed directed C-H functionalization of 2-arylindazoles with N-sulfonylformaldimines has been developed to provide a variety of N-benzylarylsulfonamide derivatives with good to excellent yields. Different activated aldehydes like ethyl glyoxalate and 2,2,2-trifluoroacetaldehyde also efficiently underwent nucleophilic addition with 2-arylindazoles. These selective transformations occur through the control of C3 nucleophilicity of indazole moiety. Mechanistic studies suggest that C-H activation step may be a rate-limiting step.