Isatoic anhydride as a masked directing group and internal oxidant for Rh(III)-catalyzed decarbonylative annulation through C-H activation: insights from DFT calculations

Density functional theory calculations uncovered a new mechanism for the rhodium-catalyzed decarbonylative annulation of isatoic anhydride with alkynes, in which the acyloxy group formed from the N-H deprotonation and C-O bond cleavage of isatoic anhydride acts as the directing group to assist the ortho C-H activation. From the generated five-membered rhodacycle intermediate, the final aminoisocoumarin product could be formed by subsequent steps of alkyne insertion, reductive elimination, decarbonylation, and protonation. The isocyanate moiety contained in the annulation intermediate was uncovered as a novel internal oxidant for the reaction, which oxidizes the Rh(I) to Rh(III) by decarbonylation.

Additive-Controlled Divergent Synthesis of Fluorenone-4-carboxylic Acids and Diphenic Anhydrides via Rhodium-Catalyzed Oxidative Dimeric Cyclization of Aromatic Acids

A rhodium-catalyzed one-pot access to valuable polycyclic frameworks of fluorenone-4-carboxylic acids and diphenic anhydrides via the oxidative dimeric cyclization of aromatic acids has been developed. This transformation proceeded via carboxyl-assisted 2-fold C-H activation followed by intramolecular Friedel-Crafts or dehydration reactions. The silver salt additive plays a vital role in the chemoselectivity of the products. Diphenic anhydride 3l exhibits a maximum fluorescence quantum yield of up to 59%.

Transition metal catalysed cascade C-C and C-O bond forming events of alkynes

The past few decades have witnessed the emergence of domino reactions as a powerful tool for the multi-functionalization of alkynes for the rapid and smooth construction of complex molecular architectures. In this context, employing transition metal catalysis, vicinal/geminal cascade functionalization of alkynes involving C-C and C-O bond-formation reactions, has become a preferred strategy for the synthesis of oxygenated motifs. Despite this significant progress, reviews documenting such strategies are either metal/functional group-centric or target-oriented, thus hampering further developments. Therefore, in this review, different conceptual approaches based on C-C and C-O bond-forming events of alkynes such as carboxygenation (C-C and CO bond formation), carboalkoxylation (C-C and C-OR bond formation), and carboacetoxylation (C-C and C-OAc bond formations) are discussed, and examples from the literature from the last two decades are presented. Further, we have presented detailed insights into the mechanism of different transformations.

Synthesis of Furans via Rhodium(III)-Catalyzed Cyclization of Acrylic Acids with α-Diazocarbonyl Compounds

An efficient protocol for the synthesis of furans through Rh(III)-catalyzed vinyl C-H activation from acrylic acids and α-diazocarbonyl compounds has been developed. The reaction features broad functional group tolerance and affords a series of furans in moderate to good yields. Moreover, no additives such as copper or silver salts are required. Some control experiments are performed to give insight into the mechanism of this cascade transformation and the decarbonylation process is involved in the formation of the furan product.

Harnessing Rhodium-Catalyzed C-H Activation: Regioselective Cascade Annulation for Fused Polyheterocycles

In the realm of transition-metal catalyzed arene functionalization, rhodium(III) catalysis is considered as exemplary due to its propensity to activate C-H bonds to obtain comprehensive molecular assembly. Herein, we demonstrate a new rhodium(III) catalyzed assembly of polyheterocyclic scaffolds via C-H activation and regioselective annulation of 4-arylbut-3-yn-1-amines with 4-hydroxy-2-alkynoates. Heterocyclization and trans-metalation prior to annulation is the key for initiation of this relay redox-neutral catalytic cascade.

Construction of isoxazolone-fused phenanthridines via Rh-catalyzed cascade C-H activation/cyclization of 3-arylisoxazolones with cyclic 2-diazo-1,3-diketones

A Rh(iii)-catalyzed cascade C-H activation/intramolecular cyclization of 3-aryl-5-isoxazolones with cyclic 2-diazo-1,3-diketones was described, leading to the formation of isoxazolo[2,3-f]phenanthridine skeletons. The protocol features the simultaneous one-pot formation of two new C-C/C-N bonds and one heterocycle in moderate-to-good yields with good functional group compatibility. It is amenable to large-scale synthesis and further transformation.

Rh-Catalyzed Annulation of Benzoic Acids, Formaldehyde, and Malonates via ortho-Hydroarylation to Indanones

A three-component reaction from readily available low-cost materials of benzoic acids, formaldehyde, and malonates for the preparation of indanones by rhodium catalysis is reported. The annulation is initiated by an ortho-hydroarylation of benzoic acids, and a Lewis acid is not required. The solvent has a significant influence to the reaction, and 2-substituted or nonsubstituted indanones are obtained by the change of solvent.

Access to 1-amino-3,4-dihydroisoquinolines via palladium-catalyzed C-H bond aminoimidoylation reaction from functionalized isocyanides

Efficient access to 1-amino-3,4-dihydroisoquinolines, through palladium-catalyzed intramolecular C-H bond aminoimidoylation of α-benzyl-α-isocyanoacetates, has been developed. Consecutive isocyanide insertion and C-H bond activation were realized with C-N and C-C bonds formation in one step under redox neutral conditions, employing O-benzoyl hydroxylamines as electrophilic amino sources.