title: Rh(V) -Nitrenoid as a Key Intermediate in Rh(III) -Catalyzed Heterocyclization by C-H Activation: A Computational Perspective on the Cycloaddition of Benzamide and Diazo Compounds.
abstract: A mechanistic study of the substituent-dependent ring formations in Rh(III) -catalyzed C-H activation/cycloaddition of benzamide and diazo compounds was carried out by using DFT calculations. The results indicated that the decomposition of the diazo is facilitated upon the formation of the five-membered rhodacycle, in which the Rh(III) center is more electrophilic. The insertion of carbenoid into Rh-C(phenyl) bond occurs readily and forms a 6-membered rhodacycle, however, the following C-N bond formation is difficult both kinetically and thermodynamically by reductive elimination from the Rh(III) species. Instead, the Rh(V) -nitrenoid intermediate could be formed by migration of the pivalate from N to Rh, which undergoes the heterocyclization much more easily and complementary ring-formations could be modulated by the nature of the substituent at the α-carbon. When a vinyl is attached, the stepwise 1,3-allylic migration occurs prior to the pivalate migration and the 8-membered ring product will be formed. On the other hand, the pivalate migration becomes more favorable for the phenyl-contained intermediate because of the difficult 1,3-allylic migration accompanied by dearomatization, thus the 5-membered ring product was formed selectively.
authors.affiliation: College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (P.R. China).
authors.forename: Tao
authors.initials: T
authors.lastname: Zhou
authors.affiliation: College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (P.R. China).
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.affiliation: College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (P.R. China). xyz@wzu.edu.cn.
authors.forename: Yuanzhi
authors.initials: Y
authors.lastname: Xia
keywords: CH activation; cycloadditions; density functional calculations; diazo compounds; rhodium