Mechanistic insight into the Rh(III)-catalyzed cascade annulation of o-ethynylanilines with diazo compounds towards Benzo[a]carbazoles

A mechanistic analysis for the reactions of Rh-III-catalyzed intermolecular cascade annulation of o-ethynylanilines with diazo compounds has been performed in details using density functional theory (DFT) calculations. It is revealed theoretically that the reaction mechanisms starting from intermediate 6 disagree with those proposed by the experimenters. The rate-determining step of the catalytic cycle is the dinitrogen elimination process with an overall barrier of 31.1 kcal mol(-1) (2 -> TS4'-5 ''), in which the difficulty of the dissociation of N-2 molecule is connected with the yields of product P. The presence of HOAc molecule is essential for cyclization process through the C-C linkage. The current calculation results expound the experimental observation at the molecular level. (C) 2018 Elsevier B.V. All rights reserved.