Site-Selective Aerobic C–H Monoacylation of Carbazoles Using Palladium Catalysis

Abstract

This manuscript describes the development of a remarkably general palladium-catalyzed monoacylation of carbazoles using toluene derivatives playing the dual role of acyl source and organic solvent. The method uses NHPI as the cocatalyst and oxygen as the sole oxidant. Interestingly, the acylation of monosubstituted N-pyridylcarbazoles takes place regioselectively at the C-8 position. The scope of the method is explored using aldehyde as the acyl source. This highly site-selective acylation proceeds through a radical process.

Recent Advances in Palladium-Catalyzed Oxidative Couplings in the Synthesis/Functionalization of Cyclic Scaffolds Using Molecular Oxygen as the Sole Oxidant

“…They employed N -hydroxyphthalimide (NHPI) as a radical initiator, toluene, oxygen as the sole oxidant, and Pd(II) catalysis (Scheme 47 ). 80 The authors explored the scope with a variety of toluene- and mono- and disubstituted N -pyridyl­carbazole derivatives, obtaining regioselective acylated products without using any additional solvent. The reaction takes place by the formation of phthalimido- N -oxyl (PINO) from NHPI and O 2 , followed by abstraction of a hydrogen from the toluene to form a benzylic radical that is rapidly oxidized by molecular oxygen leading to formation of a benzoyl radical.…”

“…They employed N-hydroxyphthalimide (NHPI) as a radical initiator, toluene, oxygen as the sole oxidant, and Pd(II) catalysis (Scheme 47). 80 The authors explored the scope with a variety of toluene-and mono-and disubstituted N-pyridyl-…”

Pd(II)‐Catalyzed Chelation‐Induced C(sp2)‐H Acylation of (Hetero)Arenes Using Toluenes as Aroyl Surrogate

“…After screening several catalysts, co‐catalyst, and oxidants, the authors recognized that 10 mol% of Pd(OAc) 2 in combination with 30 mol% of NHPI in toluene at 80 °C under air afforded the regioselective C‐8 acylation product of carbazole in best yield (Scheme 30). [46] The substrate scope of toluene derivatives was examined where electron‐deficient toluenes afforded better yields than electron‐rich toluenes. Moreover, different halogenated toluenes were also well tolerant under this condition.…”

Rhodium-catalysed decarbonylative C(sp2)–H alkylation of indolines with alkyl carboxylic acids and carboxylic anhydrides under redox-neutral conditions

“…4 Consequently, ligand-directed C-7 functionalisation of indolines has emerged as a promising alternative to the corresponding functionalisation of indoles. 5,6…”