title: Rhodium-catalyzed C-H activation of phenacyl ammonium salts assisted by an oxidizing C-N bond: a combination of experimental and theoretical studies.
abstract: Rh(III)-catalyzed C-H activation assisted by an oxidizing directing group has evolved to a mild and redox-economic strategy for the construction of heterocycles. Despite the success, these coupling systems are currently limited to cleavage of an oxidizing N-O or N-N bond. Cleavage of an oxidizing C-N bond, which allows for complementary carbocycle synthesis, is unprecedented. In this article, α-ammonium acetophenones with an oxidizing C-N bond have been designed as substrates for Rh(III)-catalyzed C-H activation under redox-neutral conditions. The coupling with α-diazo esters afforded benzocyclopentanones, and the coupling with unactivated alkenes such as styrenes and aliphatic olefins gave ortho-olefinated acetophenoes. In both systems the reactions proceeded with a broad scope, high efficiency, and functional group tolerance. Moreover, efficient one-pot coupling of diazo esters has been realized starting from α-bromoacetophenones and triethylamine. The reaction mechanism for the coupling with diazo esters has been studied by a combination of experimental and theoretical methods. In particular, three distinct mechanistic pathways have been scrutinized by DFT studies, which revealed that the C-H activation occurs via a C-bound enolate-assisted concerted metalation-deprotonation mechanism and is rate-limiting. In subsequent C-C formation steps, the lowest energy pathway involves two rhodium carbene species as key intermediates.
authors.affiliation: Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023, China.
authors.forename: Songjie
authors.initials: S
authors.lastname: Yu
authors.forename: Song
authors.initials: S
authors.lastname: Liu
authors.forename: Yu
authors.initials: Y
authors.lastname: Lan
authors.forename: Boshun
authors.initials: B
authors.lastname: Wan
authors.forename: Xingwei
authors.initials: X
authors.lastname: Li
mesh_terms: D000098:Acetophenones / Q000737:chemistry*; D064751:Ammonium Compounds / Q000737:chemistry*; D002384:Catalysis; D008958:Models, Molecular; D010084:Oxidation-Reduction; D012238:Rhodium / Q000737:chemistry*; D012492:Salts / Q000737:chemistry
chemical_list: D000098:Acetophenones; D064751:Ammonium Compounds; D012492:Salts; D012238:Rhodium