title: Computational Insights into the Rhodium(III)-Catalyzed Coupling of Benzamides and 1,6-Enynes via a Tunable Arylative Cyclization.
abstract: A density functional theory (DFT) study has been conducted to elucidate the mechanism of the rhodium(III)-catalyzed C-H activation of O-substituted N-hydroxybenzamides and cyclohexadienone-containing 1,6-enynes. The impact of different O-substituted internal oxidants (OPiv versus OMe) on the arylative cyclization (i.e., Ⓝ-Michael addition versus Ⓒ-Michael addition) has been evaluated in detail. The Ⓝ-Michael addition pathway proceeded via a Rh(I) species, while Rh(III) remained unchanged throughout the Ⓒ-Michael addition pathway. The Rh(III)/Rh(I) catalytic cycle in the Ⓝ-Michael addition pathway was different from those reported previously where the Rh(III)/Rh(V) catalytic cycle was favored for the Rh(III)-catalyzed C-H activation of O-substituted N-hydroxybenzamides. The first three steps were similar for the OPiv- and OMe-substituted substrates, which involved sequential N-H deprotonation, C-H activation (a concerted metalation-deprotonation process), and 1,6-enyne insertion steps. Starting from a seven-membered rhodacycle, the alternative mechanism would be controlled by the OR substituent. When the substituent was OMe, the unstable seven-membered rhodacycle was readily coordinated by a double bond of the cyclohexadienone which enabled the Ⓒ-Michael addition reaction. However, the presence of an N-OPiv moiety stabilized the seven-membered rhodacycle through a bidentate coordination which facilitated the Ⓝ-Michael addition process.
authors.affiliation: Department of Chemistry, Jinan University , Huangpu Road West 601, Guangzhou, Guangdong 510632, P. R. China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Du
authors.affiliation: Department of Chemistry, Jinan University , Huangpu Road West 601, Guangzhou, Guangdong 510632, P. R. China.
authors.forename: Yilu
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Chemistry, Jinan University , Huangpu Road West 601, Guangzhou, Guangdong 510632, P. R. China.
authors.forename: Shengwen
authors.initials: S
authors.lastname: Yang
authors.affiliation: Department of Chemistry, Jinan University , Huangpu Road West 601, Guangzhou, Guangdong 510632, P. R. China.
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Chemistry, Jinan University , Huangpu Road West 601, Guangzhou, Guangdong 510632, P. R. China.
authors.forename: Xionghui
authors.initials: X
authors.lastname: Fu