Rhodium(III)-Catalyzed Oxidative CH Coupling ofN-Methoxybenzamides with Aryl Boronic Acids: One-Pot Synthesis of Phenanthridinones

Directed regioselective arylation of imidazo[1,2-a]pyridine-3-carboxamides using Rh(III) catalysis

In contrast to previously reported free-radical pathways to functionalize imidazo[1,2-a]pyridines at the C-5 centre, directing group approaches are rare. Herein, we demonstrate a rhodium(III) catalyzed efficient and regioselective strategy for directed C-5 functionalization of imidazo[1,2-a]pyridines using N-methoxyamide as a directing group. This methodology facilitates directed arylation without the necessity for pre-functionalization. It also allows for gram-scale synthesis and post-functionalization.

Cp*Rh(III)-Catalyzed C-H Arylation of Ferrocenethionamides with Aryl Boronic Acids for the Synthesis of Aryl-Ferrocenes

We developed a Cp*Rh(III)-catalyzed C-H arylation of ferrocenethionamides with arylboronic acids for the synthesis of aryl-ferrocenes under mild and base-free conditions, using Ag₂ CO₃ as oxidant. The reaction results in high yields and excellent regioselectivity accommodating a broad scope of substrate range and functional group compatibility, and provides an alternative protocol for the generation of highly functionalized aryl-ferrocene compounds.

Facile Synthesis of Alkylidene Phthalides by Rhodium-Catalyzed Domino C-H Acylation/Annulation of Benzamides with Aliphatic Carboxylic Acids

The Rh-catalyzed ortho-C(sp² )-H functionalization of 8-aminoquinoline-derived benzamides with aliphatic acyl fluorides generated in situ from the corresponding acids has been developed. This reaction initiated with 8-aminoquinoline-directed ortho-C(sp² )-H acylation, which was accompanied by subsequent intramolecular nucleophilic acyl substitution of amide group to produce alkylidene phthalides This approach exhibits high stereo-selectivity for Z-isomer products, and tolerates a variety of functional groups as well as aliphatic carboxylic acids with diverse structural scaffolds.

Oxidatively Induced Selective Carbon-Carbon Bond Formation From Isolated Rhodium(III) Complexes

This work focuses on oxidatively induced regioselective intramolecular C-C bond formations based on the Rh^III complexes synthesized from dirhodium(II) trifluoroacetate with 2-arylpyridines. With the selection of electron-donating groups on the arene rings of 2-arylpyridines, the unusual meta-ortho C-C bond-forming was favored, which led to the formation of meta-substituted 2-arylpyridine homocoupling dimers. On the contrary, the electron-withdrawing groups have tendency to occur conventional ortho-ortho bond-forming, resulting in the formation of new Rh^III complexes possessing the intriguing Rh^III (TFA)₃ fragment. Preliminary mechanistic experiments suggest that the sequential oxidation of Rh^III occurred in the reaction.

Synthetic Strategies in the Preparation of Phenanthridinones

Phenanthridinones are important heterocyclic frameworks present in a variety of complex natural products, pharmaceuticals and displaying wide range of pharmacological actions. Its structural importance has evoked a great deal of interest in the domains of organic synthesis and medicinal chemistry to develop new synthetic methodologies, as well as novel compounds of pharmaceutical interest. This review focuses on the synthesis of phenanthridinone scaffolds by employing aryl-aryl, N-aryl, and biaryl coupling reactions, decarboxylative amidations, and photocatalyzed reactions.

A Cross-Dehydrogenative Annulation Strategy towards Synthesis of Polyfluorinated Phenanthridinones with Copper

The first cross-dehydrogenative annulation of (hetero)aromatic amides with polyfluoro(hetero)arenes is presented. This operationally simple oxidative annulation process is mediated by inexpensive copper salt, accommodates a wide range of substrates with exquisite chemo- and regioselectivity profile, and produces demanding polyfluorinated phenanthridinones in high yields (up to 92 %). Using alkenyl amides under identical conditions, the synthesis of polyfluorinated 2-quinolones has also been accomplished. Given the importance of fluorinated heterocycles in the pharmaceutical industry and drug discovery, this work is highly significant.

A Simple and Versatile Amide Directing Group for C-H Functionalizations

Achieving selective C-H activation at a single and strategic site in the presence of multiple C-H bonds can provide a powerful and generally useful retrosynthetic disconnection. In this context, a directing group serves as a compass to guide the transition metal to C-H bonds by using distance and geometry as powerful recognition parameters to distinguish between proximal and distal C-H bonds. However, the installation and removal of directing groups is a practical drawback. To improve the utility of this approach, one can seek solutions in three directions: 1) Simplifying the directing group, 2) using common functional groups or protecting groups as directing groups, and 3) attaching the directing group to substrates via a transient covalent bond to render the directing group catalytic. This Review describes the rational development of an extremely simple and yet broadly applicable directing group for Pd(II) , Rh(III) , and Ru(II) catalysts, namely the N-methoxy amide (CONHOMe) moiety. Through collective efforts in the community, a wide range of C-H activation transformations using this type of simple directing group have been developed.

Aniline carbamates: a versatile and removable motif for palladium-catalyzed directed C-H activation

The aniline carbamate is introduced as a new removable directing group for C-H activation. Its versatility and ability as a directing group are demonstrated by its use in the ortho-arylation of a wide variety of aniline derivatives under palladium(II) catalysis, with symmetric diaryliodonium salts as aryl donors. The reaction differs from previously reported arylations in its selectivity and its mechanism, as elucidated by kinetic and isotopic experiments. The directing group can also be easily removed under a variety of conditions.

Rh(III) -catalyzed C-H activation: a versatile route towards various polycyclic pyridinium salts

An efficient and convenient method for the synthesis of highly substituted polycyclic pyridinium salts from the reaction of various 2-aryl-pyridines and 2-aryl-sp(2) -nitrogen-atom-containing heterocycles with alkynes through rhodium(III)-catalyzed CH activation and annulation under an O2 atmosphere is described. A possible mechanism that involves the chelation-assisted CH activation of the 2-aryl-pyridine substrate, insertion of the alkyne, and reductive elimination is proposed. This mechanism was supported by the isolation of a five-membered rhodacycle (I'). In addition, kinetic isotope studies were performed to understand the intimate reaction mechanism.

Synthesis of Phenanthridinones from N-methoxybenzamides and aryltriethoxysilanes through Rh(III)-catalyzed C-H and N-H bond activation

An efficient method for the one-pot synthesis of substituted phenanthridinone derivatives from N-methoxybenzamides and aryltriethoxysilanes through rhodium-catalyzed dual C-H bond activation and annulation reactions is described. A double-cycle mechanism is proposed to account for this catalytic reaction. In addition, isotope-labeling studies were performed to understand the intimate mechanism of the reaction.