Palladium catalyzed aryl C–H amination with O₂via in situ formation of peroxide-based oxidant(s) from dioxane

Abstract

(DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramolecular aryl C–H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decomposition product of dioxane. An induction period observed for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidation of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for the palladium-catalyzed aerobic oxidation reactions conducted in ethereal solvents.

Cationic palladium(ii) complexes as catalysts for the oxidation of terminal olefins to methyl ketones using hydrogen peroxide

“…More recently, Weinstein and Stahl reported that peroxide species generated in situ from 1,4-dioxane and O 2 acted as the oxidant in palladium catalysed aryl C-H amination reactions. 34 We also tested 2-butanone as a solvent and found that this also resulted in a good yield (Entry 8 Table 2). We presumed that this further supported the idea of in situ formation of organic peroxides that are then acting as oxidants, as 2-butanone and H 2 O 2 can form 2-butanone peroxide (often referred to as MEKP (methyl ethyl ketone peroxide)).…”

Decarboxylative ipso Amination of Activated Benzoic Acids

“…The elementary steps of a Pd 0 /Pd II cycle have been seen in similar form for phosphine complexes in aminations reported by the groups of Buchwald and Hartwig . Aerobic oxidation of Pd II to Pd IV and reductive elimination with formation of a C–heteroatom bond from a Pd IV species have been postulated by Mirica and co‐workers for the oxidation of arenes to phenols and by Stahl and co‐workers for the synthesis of carbazoles by intramolecular C−N formation …”

Synthesis of Indole-2-carboxylate Derivatives via Palladium-Catalyzed Aerobic Amination of Aryl C–H Bonds

“…14 Notably, the only examples in which O 2 was used as the terminal oxidant is for carbazole synthesis, and a limited substrate scope was demonstrated under the reported conditions. 12,13d …”