Palladium-catalyzed oxidative C-H activation/annulation of N-alkylanilines with bromoalkynes: access to functionalized 3-bromoindoles

Merging of Two Photoredox Cycles with One Perovskite Catalyst Achieving Dual Functionalization: N-Heterocyclization and Site-Selective Bromination of N-Arylamines

Dual functionalization in organic synthesis represents a powerful strategy aimed at achieving multiple transformations within a single reaction cycle, thereby streamlining synthetic processes, enhancing efficiency, and imparting economic paths for complex molecules. Here, we report a heterogeneous perovskite nanocrystal (NC) photocatalytic system that can simultaneously drive two photoredox cycles in a single reaction. The dual process incorporates two distinct functional groups (N-heterocycles and bromines) into N-arylamines under the influence of a single catalyst (CsPbBr3 NCs), allowing for the concurrent formation of two distinct architectures of 3-bromo-N-arylindoles. Mechanistically, long-lived charge separation and charge carrier accumulation at the NC surface enable perovskite to drive these two photoredox cycles simultaneously. The dual approach exploits light-induced holes to drive an amine oxidation in one cycle (I) and cooperatively utilizes dibromomethane (CH2Br2), a solvent-grade mild reagent for site-selective bromination, to achieve the other photoredox cycle (II). We find that chiral perovskite induces enantioselective axial C-N bond formation, but is inactive for axial C-C bond formation of arylindoles. Merging two photoredox cycles simultaneously to achieve dual functionalization is rare; thus, the perovskite NC photocatalysis not only aligns with the principles of green chemistry but also holds immense potential for the rapid and economical design of complex molecules.

Palladium-catalyzed ligand-regulated divergent synthesis of pyrrole[2,3-b]indoles and ureas from 2-ethynylanilines and isocyanides

Herein, a palladium-catalyzed and ligand-controlled protocol for the divergent synthesis of pyrrole[2,3-b]indole and urea derivatives has been described. Pyrrole[2,3-b]indoles ("cyclization on" products) via tandem cyclization of o-alkynylanilines with isocyanides in the absence of a ligand and ureas ("cyclization off" products) via oxidative amination of anilines with isocyanides in the presence of a ligand were obtained both in moderate to good yields with high selectivity. In this chemistry, cyclic and acyclic products were easily accessed with the same starting materials under the regulation of the ligand.

Palladium-Catalyzed Tandem Cyclization of Bromoalkynes, Anilines and CO: Access to 1,3-Substituted Maleimides

A novel palladium-catalyzed three-component carbonylation reaction for the assembly of various 1,3-substituted maleimide derivatives from haloalkynes and simple anilines. The nucleophilic addition reaction of haloalkynes, anilines and CO, and insertion of carbonyl have been achieved sequentially in this reaction. The high chemo- and regioselectivities, as well as no need of expensive ligands or additives further illustrate the synthetic value of this approach.

Palladium-Catalyzed Tandem Nucleophilic Addition/C-H Functionalization of Anilines and Bromoalkynes for the Synthesis of 2-Phenylindoles

A novel and efficient palladium-catalyzed annulation of anilines with bromoalkynes for the synthesis of 2-phenylindoles has been described. This approach features excellent regio- and stereoselectivities and good functional group tolerance. Preliminary mechanistic studies indicate that anilines undergo anti-nucleophilic addition to bromoalkynes to generate (Z)-N-(2-bromo-1-phenylvinyl) anilines, followed by sequential C-H functionalization to deliver different substituted 2-phenylindoles. This method provides potential applications for the construction of various biologically active compounds.

Transition-metal-free Synthesis of tetra-substituted Vinyl Iodides by Cascade Sequential Reaction of α-Keto Acids, 1-Iodoalkynes, and Alkyl Halides

The cascade sequential reaction of α-keto acids, 1-iodoalkynes, and alkyl halides are reported herein to synthesize tetra-substituted vinyl iodides. It represents an efficient protocol to access a diverse range of tetra-substituted vinyl iodides starting from simple materials in a one-pot fashion, featuring mild reaction conditions, ease of operation, and broad substrate scope.