Palladium-mediated intramolecular O-arylation: a simple route for the synthesis of quino[2,3-c] and quino[3,2-b]carbazoles

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.

Transition-Metal-Free Access to Pyridocarbazoles from 2-Alkynylindole-3-carbaldehydes via Azomethine Ylide

An efficient approach for the synthesis of functionalized tetrahydro-pyrido/quinolinocarbazoles from 2-alkynylindole-3-carbaldehydes and l-proline utilizing a metal-free decarboxylative cyclization, ring expansion, and ring contraction strategy via the generation of azomethine ylide was developed. The reaction of 2-alkynylindole-3-carbaldehydes with l-thioproline leads to the formation of γ-carbolines. By virtue of this expedient method, a diverse range of biologically active heteroannulated carbazoles can be synthesized efficiently.

Application of sequential Cu(I)/Pd(0)-catalysis to solution-phase parallel synthesis of combinatorial libraries of dihydroindeno[1,2-c]isoquinolines

Parallel solution-phase synthesis of combinatorial libraries of dihydroindenoisoquinolines employing a sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol was realized. The scope and limitations of the protocol with respect to the substitution pattern in the aryl ring of the indene core, as well as the N-substituent have been defined, revealing that the methodology is compatible with a wide-range of aliphatic linear, branched, and ester functionalized N-substituents. Unexpectedly, the formation of regioisomers featuring a 1,2,3-contiguous substitution pattern in the aromatic ring of the indene core was observed. Three distinct combinatorial libraries with a total of 111 of members were synthesized, and 80 highly substituted dihydroindenoisoquinolines structurally related to known medicinal agents including some consisting of mixtures of two regioisomers were made available for biological activity testing.