Theoretical studies on Rh(III)-catalyzed regioselective C-H bond cyanation of indole and indoline

Density functional theory calculations were carried out to study the reaction mechanism of the Rh(III)-catalyzed regioselective C-H cyanation of indole and indoline with N-cyano-N-phenyl-para-methylbenzenesulfonamide (NCTS). This mechanism involves four major steps: C-H activation, cyano group insertion, beta-N elimination, and regeneration of active species. How different indole and indoline substrates affect the regioselectivity of C-H bond cyanation has been examined and analyzed in detail. Our calculation results indicate that the regioselectivity of C-H bond cyanation of indole depends on the nucleophilicity of carbon atoms in C-Rh(III) bonds to the cyano group. For indoline, it can be attributed to the different hybridization platforms of the C-H bond activation.