Temporary (P[double bond, length as m-dash]O) directing group enabled carbazole ortho arylation via palladium catalysis

Transition Metal-Catalyzed Direct Functionalization of Carbazoles

Carbazoles are an important class of nitrogen-containing heterocycles found in diverse natural products, bioactive molecules, and functional materials. Their broader applications have driven extensive research into their synthesis and functionalization. Among various approaches, transition metal-catalyzed C-H activation has emerged as a powerful tool for direct functionalization, offering regioselectivity, efficiency, and sustainability. This review comprehensively summarizes advancements in transition metal-catalyzed C-H functionalization of carbazoles. Various catalytic systems employing palladium, ruthenium, rhodium, nickel, cobalt, copper, and iron have enabled alkylation, alkenylation, acylation, arylation, alkynylation, and heteroatom incorporation in carbazoles. These methodologies enabled late-stage diversification and have opened avenues for accessing structurally complex carbazole derivatives with tailored properties. The review aims to provide a comprehensive guide for researchers exploring carbazole functionalization via C-H activation, highlighting key mechanistic insights, scope, and emerging trends in this field.

DBU-promoted cascade phosphorylation/cyclization for the synthesis of phosphorylated 3-aminoindoles

A novel strategy of cascade phosphorylation cyclization of 2-isocyanobenzonitrile with phosphine oxide via a DBU-promoted process has been developed. A series of phosphorylated 3-aminoindoles were constructed by forming C-C, C-P and N-P bonds and an amino group in one pot. A plausible reaction mechanism has been proposed based on step-by-step control experiments and 31P NMR analysis.

Chiral α-Aminophosphonates as Ligands in Copper-Catalyzed Asymmetric Oxidative Coupling of 2-Naphthols

Chiral α-aminophosphonates with adjacent carbon and phosphonate stereogenic centers have been employed as ligands in the copper-catalyzed oxidative coupling of 2-naphthols, resulting in the production of chiral BINOLs in favorable yields and moderate to good enantiomeric excess. This represents the first application of chiral P-based ligands to enable such a transformation. The synthesis of these chiral α-aminophosphonate ligands offers a significant advantage over approaches that typically necessitate elaborate synthetic processes for chiral ligand production.

Substituent-controlled regioselective arylation of carbazoles using dual catalysis

Regioselective arylation of carbazoles is reported using dual palladium-photoredox catalysis. Controlled monoarylation and diarylation of symmetrical and unsymmetrical carbazoles were achieved under mild reaction conditions with a broad substrate scope and functional group tolerance. Steric and electronic control the regioselectivity of the arylation of unsymmetrical carbazoles. Late-stage functionalization of a caprofen drug derivative and large-scale synthesis of mono- and di-arylated carbazoles were demonstrated to showcase the synthetic versatility of the method. Finally, we also showcased the synthesis of hyellazole analogues (a marine alkaloid) in a short route using our strategy.

Direct formation of 4,5-disubstituted carbazoles via regioselective dilithiation

Carbazoles are widely exploited for their interesting photophysical and electronic properties, however bay (4,5-) functionalization is challenging, and previously inaccessible through carbazole C-H activation. We report a simple methodology which introduces a range of versatile 4,5-functionality, enabling the wider investigation of ring annulation and close proximity effects on carbazole properties.

Harnessing the chemistry of 4aH-carbazoles: a consecutive rearrangements approach to carbazoles

We report a mild method for the synthesis of 4aH-carbazole intermediates with significant synthetic flexibility and variability, and demonstrate the controllable rearrangements of such intermediates to carbazoles.